the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Oct 2025
The first magnetic observatory of Honduras: Assessment and magnetic prospecting in 2019–2025
Abstract. Since 2017, the Departments of Astronomy and Astrophysics and Earth Physics at the National Autonomous University of Honduras have led efforts to establish the First Magnetic Observatory of Honduras, which is intended to provide continuous, precise, and permanent measurements of the Earth’s magnetic field in the region. This initiative aims to supply critical data to the international scientific and commercial sectors. However, the project has faced significant challenges, including difficulties in locating a site that satisfies the strict requirements of magnetic observatories, bureaucratic inefficiencies, insufficient financial support, limited local engagement, and restrictions imposed by the COVID-19 pandemic. This paper highlights the importance of constructing a magnetic observatory in Honduras. It provides an in-depth analysis of four candidate sites: La Tigra National Park, Francisco Morazán (14° 13' 7.24", -87° 5' 16.87"); the First Communications Battalion in Las Mesas, San Antonio de Oriente, Francisco Morazán (14° 2' 23.42", -86° 56' 19.82"); the Francisco Morazán Hydroelectric Power Station in Cortés (15° 02' 07", -87° 45' 04"); and the First Artillery Battalion in Zambrano, Francisco Morazán (14° 15' 09", -87° 25' 23"). The primary objective of this initial stage is to identify a vandalism-free site that meets the stringent magnetic cleanliness criteria required for the installation of an observatory. This process follows the guidelines of the Manual for Magnetic Measurements and Observatory Practices developed by the International Association of Geomagnetism and Aeronomy, along with expert recommendations from the INTERMAGNET Digital Geomagnetic Observatories network. The planned instrumentation will enable the observatory to (a) measure the Earth’s natural magnetic field vector free from anthropogenic interference; (b) collect continuous, broadband, absolute, long-term time series data; and (c) monitor the local geomagnetic field and solar-geomagnetic activity on a continuous basis. To achieve these objectives, a multidisciplinary team of faculty and students from the Faculties of Space Sciences and Sciences, in collaboration with experts from the British Geological Survey, has been assembled. Local personnel also gained valuable experience in magnetometry. Furthermore, offers of magnetometer equipment have been received from the Institute of Geophysics at the National Autonomous University of Mexico, Conrad Observatory in Austria, and INTERMAGNET Digital Geomagnetic Observatories network.
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AC1: 'Comment on egusphere-2025-2319', Yvelice Castillo, 07 Dec 2025
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AC2: 'Reply on AC1', Yvelice Castillo, 13 Apr 2026
REPLY TO REFEREE COMMENTS OF 23 JANUARY 2026
The manuscript primarily recounts the extensive work the team conducted in Honduras for electromagnetic detection. It reads more like an engineering report than a research paper.
Reply: In this version, the wording has been revised to make it more suitable for a scientific article.
Regarding the content, the following questions and suggestions are raised:
- The article mentions the team's geomagnetic detection work in Honduras. The obtained geomagnetic data should be analyzed in depth to reveal substantial advantages and compare it with other sites, rather than providing superficial analysis or simply using others' data for explanation.
Reply: A deeper and rigorous analysis of the prospecting data is presented.
- The article devotes considerable space to describing the difficulties and challenges of the work; it is recommended to reduce this section appropriately.
Reply: These arguments were removed.
- What is the magnitude and three components of the geomagnetic intensity at the selected location?
Reply: A definitive site was not presented because we do not have enough information for selecting it. However, thanks to the geology characterization of the sites, it is recommended to do prospecting in the deeper tunnels of the Francisco Morazán dam, due the are located into a limestone formation. There a continuous measurement of the magnetic vector components must be done.
- The key specifications of the equipment selected during the survey should be listed.
Reply: The specification of the magnetometers and other instruments were added.
- If a geomagnetic observatory were to be built at the selected location, what are the plans and arrangements, and what equipment will be deployed?
The donors consulted have stipulated that the facilities must be completed before the equipment is delivered. The equipment in question may vary depending on the donor and the time the facilities will be completed.
REPLY TO REFEREE COMMENTS OF DECEMBER 2025
Global comments
This study reports on an important effort to identify a suitable site for the installation of the first magnetic observatory in Honduras. The relevance of such an infrastructure is clearly explained, as it enables both the monitoring of the secular variation of the Earth’s main magnetic field and the observation of geomagnetic activity associated with interactions with energetic particles from the Sun, which may pose risks to various types of man-made infrastructure.
Due to a range of difficulties encountered throughout the project—such as the need to coordinate with multiple institutions, limited funding for instrumentation, lack of prior experience in this field, the COVID-19 pandemic, and the presence of different sources of perturbations at the tested sites—the project extended over a period of six years.
Although the relevance of this type of study is fully acknowledged, the submitted manuscript largely reads as a report of the work carried out and lacks a deeper and more rigorous analysis of the data acquired during the various surveys. Moreover, even as a report, it lacks clarity in several points, as detailed below.
Reply: In this version, the wording has been revised to make it more suitable for a scientific article. A deeper and rigorous analysis of the prospecting data is presented.
The manuscript also does not lead to a clear final choice for the new magnetic observatory. The apparently best candidate site, Zambrano Mountain, still requires additional testing, particularly with respect to the presence of magnetized rocks, the influence of a nearby power line, and various logistical challenges.
Reply: We realized that more prospecting and testing is needed, and we are proposing to do prospecting at the Francisco Morazán dam deeper tunnels, because they are located inside a limestone formation. Therefore, they would be good candidates to install the magnetic observatory.
In addition, electrical soundings would be required to properly characterize the lateral variability and depth profile of the local ground conductivity.
Reply: We added this at the Recommendations section.
Main issues in the manuscript:
- A geological and lithological characterization of the surveyed region is missing, including an assessment of its tectonic setting. Such information is essential for understanding the distribution of undesirably strong crustal magnetization and for identifying the most suitable locations within limestone terrains.
Reply: The geological characterizations were added to the article.
- We understand that a great effort has been made over six years through multiple surveys. However, the manuscript gives too much emphasis to reporting all the given steps and lacks a more rigorous analysis of data that could yield results of broader interest to other teams facing similar challenges. For instance, in the case of the First Communications Battalion site, a substantial amount of survey data is available (including aerial and ground magnetic profiles as well as mesh surveys), covering an area of approximately 400 × 600 m. Why has no attempt been made to integrate these datasets into a single magnetic anomaly map?
Reply: Anomaly maps were added for data measured during calm days.
- In some cases, a surveyed site is dismissed not on the basis of the magnetic survey data presented in the manuscript, but rather on the basis of other information that is not sufficiently discussed. For example, the rejection of the Mirador mine site appears to rely on the reportedly high humidity levels inside the mine. Were these values compared with those observed at established observatories, such as Conrad Observatory or observatories located in Arctic regions? Similarly, concerns related to the 50 Hz signal from the Francisco Morazan power station are mentioned. Was a variometer operated in a continuous monitoring mode over a sufficiently long period to properly assess this disturbance?
Reply: We added other reasons to explain why the Mirador mine was rejected. First, this area is very popular for hiking; second, the properties are privately owned, not government-owned; third, the equipment that was to be donated would rust easily due to the humidity; fourth, access is somewhat difficult; fifth, there isn’t enough security in the area; and the electrical supply is not easy to install.
In the Recommendations section we added that a continuous measurement of the magnetic components must be done in the selected site (in this case, the deeper tunnel of the Francisco Morazán dam).
- Several of the maps remain insufficiently informative. In particular, contour maps presented in the Appendix of the original submission reveal more clearly the magnetic gradients than the revised figures uploaded on 7 December. In addition, figures using background raster images (Figs. 5, 7, and 9 in version 2) fail to clearly distinguish profiles from meshes, and mix two colour scales, resulting in a confusing visual representation.
Reply: All contour maps and bubble maps were corrected as recommended.
- It is difficult to evaluate distances when using latitude and longitude in the coordinate axis, as is the case in most figures. Better to use meters (m) instead.
Reply: geographical coordinates were substituted by UTM coordinates.
- A diurnal correction is mentioned in the legends of Figures 6 and 8. Which magnetic observatory, or variometer station, was used to this end?
Reply: All data were corrected by diurnal variation using the total magnetic field intensity of the Magnetic Observatory of San Juan, Puerto Rico, with 1 second cadence.
- The ‘Recommendations’ presented in Section 3.11 largely reflect common knowledge within the geomagnetic community and are not directly supported by the findings of this study.
Reply: Recommendations were changed.
- The ‘Conclusions’ in Section 4 focus primarily on the general motivation for this type of study, as introduced earlier in the manuscript, while a clearer link to the specific results of the present work would strengthen this section.
Reply: Conclusions were corrected, based in the analysis of the results.
Specific issues: Note that line and figure numbers below refer to version 2 of the manuscript, uploaded on the 7th December.
- lines 30-31: ‘...guidelines of the ‘Guide for Magnetic Measurements and Observatory Practice’ published by the International ...’; Substituted
- lines 37-41: Text starting at ‘Furthermore, offers of ...’ should be removed from the abstract; Removed
- line 55: ‘...crust, geomagnetically induced currents in power lines, railways and pipelines, archeological ...”; Substituted
- lines 82-83: ‘...more observatories, improving their spatial distribution across the planet, providing for better instrumentation, with reduced noise levels, improving temporal and amplitude precision. It requires well-trained personnel, continuity of data, robust...’ Substituted
- line 100: Delete ‘modulus’; Deleted
- line 107-112: What about a scalar magnetometer? a scalar proton magnetometer…
- line 120: ’...The site should exhibit minimal spatial gradients.’ Substituted
- lines 164-165: In Figure 1, it would improve clarity to color stars differently from
triangles. Colour was added to the stars and triangles.
- lines 175-176: ‘...These should not exceed 1nT/m, at the location of the absolute
measurement instruments, measured with...’ Corrected.
- lines 187-188: ‘... foundations such as the ???’ Amitigra Foundation.
- Section 3: For clarity, the numbering of the study sites should be consistent with Table. Accordingly, Section 3.1 should refer to sites # 1-4, Section 3.2 to sites # 5-6, Section 3.3.1 to site # 7, Section 3.3.2 to site # 8, and so on; Headers and numbering were added to Table, corresponding to section 3 numbering.
- line 239: Which ‘issues’ were identified? First, this area is very popular for hiking; second, the properties are privately owned, not government-owned; third, the equipment that was to be donated would rust easily due to the humidity; fourth, access is somewhat difficult; fifth, there isn’t enough security in the area; and the electrical supply is not easy to install.
- line 245: Reference to Figure 3 appears in the text before Figure 2. This should be corrected. All previous, except Figure 1 were eliminated and substituted by others.
- line 246: ‘... presents a contour plot of the magnetic field intensity F from data measured on...’ Substituted
- line 247: Elevation contours are not seen in figures 3 or 4. I don’t think they are required, but they are mentioned in the text. Why is it expected a correlation between elevation and F contours? We don’t see such a correlation in Figures 5, 6, 8, 10... No elevations were measured for the Figures 3 and 4. Previous referee asked to include the elevations because he says that a correlation exists between the slope angle and the F values.
- line 250: Not clear what is meant by ‘bottom of Figure 3’; This figure was eliminated.
- lines 259-260: The choice of the exterior site to make a profile seems to have been made based on where internal and external reference points coincide. Please explain the importance of the measurements represented in Figure 2. It is missing information on the magnetic measurements along the mine axis. Profiles inside and outside the mine were added as a right panel of Figure 2. This panel shows the magnetic profiles along the main axis (green and black), and an outside profile over the main axis, done with the aid of the total station (see Figure 3). Besides the exterior has large anomalies, the mine’s interior has low magnetic gradients, but its length is only about 70 meters.
- line 270: Does Figure 3 represent mesh # 3 in Table 2? Please clarify in the legend. Corrected. Does Figure 4 represent mesh #7? Corrected. Needs also to be made clear. In Legend of Figure 3, ‘Elevated’ should be ‘Highest’ (substituted). Note that the ‘background’ value removed is different in Figures 3 and 4. Is this a mistake? New background values are 36000 nT.
- line 282: It doesn’t seem necessary to add Table 3, since it has one single row. Table was removed.
- lines 284-286: Not clear why this site was discarded. Needs a more careful explanation, based on the magnetic measurements that were obtained. What was the altitude of the survey? Unfortunately, the drone did not complete its scheduled flight, and the measurements present significant anomalies. Additionally, moderate pedestrian activity was observed during the prospecting (anthropogenic noise).
- line 313: Correct to ‘(Table 4: survey Figures 5, 6(a) and 6(b)).’ (Table 3, Figures 5 and 6)
- line 313: ‘...anomalies persisted, which were attributed to...’ Corrected
- line 319: Figure 5: It is expected that aerial magnetic values are lower than ground values. But why are TOTAL mesh values as low as the aerial values? The TOTAL plot was corrected. It presents lower and larger than the aerial prospecting. Also, what is the altitude of the aerial survey? The aerial survey was performed at just 29 m altitude. Profile 3 is missing. The mesh polygons are not clearly delineated. New plots were done.
- line 320: The elevation contours in figures 6a-f, make it difficult to identify clearly the magnetic anomalies. Better figures can be found in the Annexes of the first submitted version of the manuscript (figures 14, 16, 17, 18). Note that although Figures 6b–d cover overlapping regions, the magnetic contours differ significantly. Also, Figure 6f) is the representation of a mesh of points, although it is labeled as representing profiles 11, 12, and 13. Elevation contours were removed. Diurnal variation correction was done. Magnetic anomalies maps were done.
- lines 342-346: Why is the path of the shown profiles so irregular, and why do magnetic measurements oscillate so much? It is missing a discussion on the obtained results. We had to follow the path because the undergrowth was very thick and access to the mountain was very difficult. The significant anomalies are due to the presence of buried foreign materials left over from the construction of the dam.
- lines 355-356: Shouldn’t it be Figures 9 instead of Figures 18? Corrected
line 358: What does it mean ‘daily prospecting contour plots’? Corrected as plots corrected by daily variation using the total magnetic field intensity of the Magnetic Observatory of San Juan, Puerto Rico. Note in Table 2 that geomagnetic storms occurred during some prospecting.
- lines 360-362: Figure 9 is missing the location of the best site to install the observatory; profile 19 is also missing; profiles 10a and 10b are missing. Figures were corrected and profiles were added.
- lines 362-364: Figure 10: These figures are very rough and need to be worked out. Profiles # 10, 11, and 12 are represented as meshes; there seems to be some mistake. Figures corrected.
- Section 3.9: How is this information related to the installation of a magnetic observatory? This section was removed.
- line 478: Alexandra Pais did not conceive this project. Please correct. Corrected
Citation: https://doi.org/10.5194/egusphere-2025-2319-AC2 -
AC3: 'Reply on AC1', Yvelice Castillo, 13 Apr 2026
REPLY TO REFEREE COMMENTS OF DECEMBER 2025
Global comments
This study reports on an important effort to identify a suitable site for the installation of the first magnetic observatory in Honduras. The relevance of such an infrastructure is clearly explained, as it enables both the monitoring of the secular variation of the Earth’s main magnetic field and the observation of geomagnetic activity associated with interactions with energetic particles from the Sun, which may pose risks to various types of man-made infrastructure.
Due to a range of difficulties encountered throughout the project—such as the need to coordinate with multiple institutions, limited funding for instrumentation, lack of prior experience in this field, the COVID-19 pandemic, and the presence of different sources of perturbations at the tested sites—the project extended over a period of six years.
Although the relevance of this type of study is fully acknowledged, the submitted manuscript largely reads as a report of the work carried out and lacks a deeper and more rigorous analysis of the data acquired during the various surveys. Moreover, even as a report, it lacks clarity in several points, as detailed below.
Reply: In this version, the wording has been revised to make it more suitable for a scientific article. A deeper and rigorous analysis of the prospecting data is presented.
The manuscript also does not lead to a clear final choice for the new magnetic observatory. The apparently best candidate site, Zambrano Mountain, still requires additional testing, particularly with respect to the presence of magnetized rocks, the influence of a nearby power line, and various logistical challenges.
Reply: We realized that more prospecting and testing is needed, and we are proposing to do prospecting at the Francisco Morazán dam deeper tunnels, because they are located inside a limestone formation. Therefore, they would be good candidates to install the magnetic observatory.
In addition, electrical soundings would be required to properly characterize the lateral variability and depth profile of the local ground conductivity.
Reply: We added this at the Recommendations section.
Main issues in the manuscript:
- A geological and lithological characterization of the surveyed region is missing, including an assessment of its tectonic setting. Such information is essential for understanding the distribution of undesirably strong crustal magnetization and for identifying the most suitable locations within limestone terrains.
Reply: The geological characterizations were added to the article.
- We understand that a great effort has been made over six years through multiple surveys. However, the manuscript gives too much emphasis to reporting all the given steps and lacks a more rigorous analysis of data that could yield results of broader interest to other teams facing similar challenges. For instance, in the case of the First Communications Battalion site, a substantial amount of survey data is available (including aerial and ground magnetic profiles as well as mesh surveys), covering an area of approximately 400 × 600 m. Why has no attempt been made to integrate these datasets into a single magnetic anomaly map?
Reply: Anomaly maps were added for data measured during calm days.
- In some cases, a surveyed site is dismissed not on the basis of the magnetic survey data presented in the manuscript, but rather on the basis of other information that is not sufficiently discussed. For example, the rejection of the Mirador mine site appears to rely on the reportedly high humidity levels inside the mine. Were these values compared with those observed at established observatories, such as Conrad Observatory or observatories located in Arctic regions? Similarly, concerns related to the 50 Hz signal from the Francisco Morazan power station are mentioned. Was a variometer operated in a continuous monitoring mode over a sufficiently long period to properly assess this disturbance?
Reply: We added other reasons to explain why the Mirador mine was rejected. First, this area is very popular for hiking; second, the properties are privately owned, not government-owned; third, the equipment that was to be donated would rust easily due to the humidity; fourth, access is somewhat difficult; fifth, there isn’t enough security in the area; and the electrical supply is not easy to install.
In the Recommendations section we added that a continuous measurement of the magnetic components must be done in the selected site (in this case, the deeper tunnel of the Francisco Morazán dam).
- Several of the maps remain insufficiently informative. In particular, contour maps presented in the Appendix of the original submission reveal more clearly the magnetic gradients than the revised figures uploaded on 7 December. In addition, figures using background raster images (Figs. 5, 7, and 9 in version 2) fail to clearly distinguish profiles from meshes, and mix two colour scales, resulting in a confusing visual representation.
Reply: All contour maps and bubble maps were corrected as recommended.
- It is difficult to evaluate distances when using latitude and longitude in the coordinate axis, as is the case in most figures. Better to use meters (m) instead.
Reply: geographical coordinates were substituted by UTM coordinates.
- A diurnal correction is mentioned in the legends of Figures 6 and 8. Which magnetic observatory, or variometer station, was used to this end?
Reply: All data were corrected by diurnal variation using the total magnetic field intensity of the Magnetic Observatory of San Juan, Puerto Rico, with 1 second cadence.
- The ‘Recommendations’ presented in Section 3.11 largely reflect common knowledge within the geomagnetic community and are not directly supported by the findings of this study.
Reply: Recommendations were changed.
- The ‘Conclusions’ in Section 4 focus primarily on the general motivation for this type of study, as introduced earlier in the manuscript, while a clearer link to the specific results of the present work would strengthen this section.
Reply: Conclusions were corrected, based in the analysis of the results.
Specific issues: Note that line and figure numbers below refer to version 2 of the manuscript, uploaded on the 7th December.
- lines 30-31: ‘...guidelines of the ‘Guide for Magnetic Measurements and Observatory Practice’ published by the International ...’; Substituted
- lines 37-41: Text starting at ‘Furthermore, offers of ...’ should be removed from the abstract; Removed
- line 55: ‘...crust, geomagnetically induced currents in power lines, railways and pipelines, archeological ...”; Substituted
- lines 82-83: ‘...more observatories, improving their spatial distribution across the planet, providing for better instrumentation, with reduced noise levels, improving temporal and amplitude precision. It requires well-trained personnel, continuity of data, robust...’ Substituted
- line 100: Delete ‘modulus’; Deleted
- line 107-112: What about a scalar magnetometer? a scalar proton magnetometer…
- line 120: ’...The site should exhibit minimal spatial gradients.’ Substituted
- lines 164-165: In Figure 1, it would improve clarity to color stars differently from
triangles. Colour was added to the stars and triangles.
- lines 175-176: ‘...These should not exceed 1nT/m, at the location of the absolute
measurement instruments, measured with...’ Corrected.
- lines 187-188: ‘... foundations such as the ???’ Amitigra Foundation.
- Section 3: For clarity, the numbering of the study sites should be consistent with Table. Accordingly, Section 3.1 should refer to sites # 1-4, Section 3.2 to sites # 5-6, Section 3.3.1 to site # 7, Section 3.3.2 to site # 8, and so on; Headers and numbering were added to Table, corresponding to section 3 numbering.
- line 239: Which ‘issues’ were identified? First, this area is very popular for hiking; second, the properties are privately owned, not government-owned; third, the equipment that was to be donated would rust easily due to the humidity; fourth, access is somewhat difficult; fifth, there isn’t enough security in the area; and the electrical supply is not easy to install.
- line 245: Reference to Figure 3 appears in the text before Figure 2. This should be corrected. All previous, except Figure 1 were eliminated and substituted by others.
- line 246: ‘... presents a contour plot of the magnetic field intensity F from data measured on...’ Substituted
- line 247: Elevation contours are not seen in figures 3 or 4. I don’t think they are required, but they are mentioned in the text. Why is it expected a correlation between elevation and F contours? We don’t see such a correlation in Figures 5, 6, 8, 10... No elevations were measured for the Figures 3 and 4. Previous referee asked to include the elevations because he says that a correlation exists between the slope angle and the F values.
- line 250: Not clear what is meant by ‘bottom of Figure 3’; This figure was eliminated.
- lines 259-260: The choice of the exterior site to make a profile seems to have been made based on where internal and external reference points coincide. Please explain the importance of the measurements represented in Figure 2. It is missing information on the magnetic measurements along the mine axis. Profiles inside and outside the mine were added as a right panel of Figure 2. This panel shows the magnetic profiles along the main axis (green and black), and an outside profile over the main axis, done with the aid of the total station (see Figure 3). Besides the exterior has large anomalies, the mine’s interior has low magnetic gradients, but its length is only about 70 meters.
- line 270: Does Figure 3 represent mesh # 3 in Table 2? Please clarify in the legend. Corrected. Does Figure 4 represent mesh #7? Corrected. Needs also to be made clear. In Legend of Figure 3, ‘Elevated’ should be ‘Highest’ (substituted). Note that the ‘background’ value removed is different in Figures 3 and 4. Is this a mistake? New background values are 36000 nT.
- line 282: It doesn’t seem necessary to add Table 3, since it has one single row. Table was removed.
- lines 284-286: Not clear why this site was discarded. Needs a more careful explanation, based on the magnetic measurements that were obtained. What was the altitude of the survey? Unfortunately, the drone did not complete its scheduled flight, and the measurements present significant anomalies. Additionally, moderate pedestrian activity was observed during the prospecting (anthropogenic noise).
- line 313: Correct to ‘(Table 4: survey Figures 5, 6(a) and 6(b)).’ (Table 3, Figures 5 and 6)
- line 313: ‘...anomalies persisted, which were attributed to...’ Corrected
- line 319: Figure 5: It is expected that aerial magnetic values are lower than ground values. But why are TOTAL mesh values as low as the aerial values? The TOTAL plot was corrected. It presents lower and larger than the aerial prospecting. Also, what is the altitude of the aerial survey? The aerial survey was performed at just 29 m altitude. Profile 3 is missing. The mesh polygons are not clearly delineated. New plots were done.
- line 320: The elevation contours in figures 6a-f, make it difficult to identify clearly the magnetic anomalies. Better figures can be found in the Annexes of the first submitted version of the manuscript (figures 14, 16, 17, 18). Note that although Figures 6b–d cover overlapping regions, the magnetic contours differ significantly. Also, Figure 6f) is the representation of a mesh of points, although it is labeled as representing profiles 11, 12, and 13. Elevation contours were removed. Diurnal variation correction was done. Magnetic anomalies maps were done.
- lines 342-346: Why is the path of the shown profiles so irregular, and why do magnetic measurements oscillate so much? It is missing a discussion on the obtained results. We had to follow the path because the undergrowth was very thick and access to the mountain was very difficult. The significant anomalies are due to the presence of buried foreign materials left over from the construction of the dam.
- lines 355-356: Shouldn’t it be Figures 9 instead of Figures 18? Corrected
line 358: What does it mean ‘daily prospecting contour plots’? Corrected as plots corrected by daily variation using the total magnetic field intensity of the Magnetic Observatory of San Juan, Puerto Rico. Note in Table 2 that geomagnetic storms occurred during some prospecting.
- lines 360-362: Figure 9 is missing the location of the best site to install the observatory; profile 19 is also missing; profiles 10a and 10b are missing. Figures were corrected and profiles were added.
- lines 362-364: Figure 10: These figures are very rough and need to be worked out. Profiles # 10, 11, and 12 are represented as meshes; there seems to be some mistake. Figures corrected.
- Section 3.9: How is this information related to the installation of a magnetic observatory? This section was removed.
- line 478: Alexandra Pais did not conceive this project. Please correct. Corrected
Citation: https://doi.org/10.5194/egusphere-2025-2319-AC3
-
AC2: 'Reply on AC1', Yvelice Castillo, 13 Apr 2026
-
RC1: 'Comment on egusphere-2025-2319', Anonymous Referee #1, 02 Jan 2026
Global comments
This study reports on an important effort to identify a suitable site for the installation of the first magnetic observatory in Honduras. The relevance of such an infrastructure is clearly explained, as it enables both the monitoring of the secular variation of the Earth’s main magnetic field and the observation of geomagnetic activity associated with interactions with energetic particles from the Sun, which may pose risks to various types of man-made infrastructure.
Due to a range of difficulties encountered throughout the project—such as the need to coor- dinate with multiple institutions, limited funding for instrumentation, lack of prior experience in this field, the COVID-19 pandemic, and the presence of different sources of perturbations at the tested sites—the project extended over a period of six years.
Although the relevance of this type of study is fully acknowledged, the submitted manuscript largely reads as a report of the work carried out and lacks a deeper and more rigorous analysis of the data acquired during the various surveys. Moreover, even as a report, it lacks clarity in several points, as detailed below.
The manuscript also does not lead to a clear final choice for the new magnetic observatory. The apparently best candidate site, Zambrano Mountain, still requires additional testing, par- ticularly with respect to the presence of magnetized rocks, the influence of a nearby power line, and various logistical challenges. In addition, electrical soundings would be required to properly characterize the lateral variability and depth profile of the local ground conductivity.
Main issues in the manuscript:
-
A geological and lithological characterization of the surveyed region is missing, including an assessment of its tectonic setting. Such information is essential for understanding the distribution of undesirably strong crustal magnetization and for identifying the most suitable locations within limestone terrains.
-
We understand that a great effort has been made over six years through multiple surveys. However, the manuscript gives too much emphasis to reporting all the given steps and lacks a more rigorous analysis of data that could yield results of broader interest to other teams facing similar challenges. For instance, in the case of the First Communications Battalion site, a substantial amount of survey data is available (including aerial and ground magnetic profiles as well as mesh surveys), covering an area of approximately 400 × 600 m. Why has no attempt been made to integrate these datasets into a single magnetic anomaly map?
-
In some cases, a surveyed site is dismissed not on the basis of the magnetic survey data presented in the manuscript, but rather on the basis of other information that is not sufficiently discussed. For example, the rejection of the Mirador mine site appears to rely on the reportedly high humidity levels inside the mine. Were these values compared with those observed at established observatories, such as Conrad Observatory or observatories located in Arctic regions? Similarly, concerns related to the 50 Hz signal from the Francisco Moraz ́an power station are mentioned. Was a variometer operated in a continuous monitoring mode over a sufficiently long period to properly assess this disturbance?
-
Several of the maps remain insufficiently informative. In particular, contour maps presented in the Appendix of the original submission reveal more clearly the magnetic gradients than the revised figures uploaded on 7 December. In addition, figures using background raster images (Figs. 5, 7, and 9 in version 2) fail to clearly distinguish profiles from meshes, and mix two colour scales, resulting in a confusing visual representation.
-
It is difficult to evaluate distances when using latitude and longitude in the coordinate axis, as is the case in most figures. Better to use meters (m) instead.
-
A diurnal correction is mentioned in the legends of Figures 6 and 8. Which magnetic observatory, or variometer station, was used to this end?
-
The ‘Recommendations’ presented in Section 3.11 largely reflect common knowledge within the geomagnetic community and are not directly supported by the findings of this study.
-
The ‘Conclusions’ in Section 4 focus primarily on the general motivation for this type of study, as introduced earlier in the manuscript, while a clearer link to the specific results of the present work would strengthen this section.
Specific issues: Note that line and figure numbers below refer to version 2 of the manuscript, uploaded on the 7th December.
-
lines 30-31: ‘...guidelines of the ‘Guide for Magnetic Measurements and Observatory Practice’ published by the International ...’;
-
lines 37-41: Text starting at ‘Furthermore, offers of ...’ should be removed from the abstract;
-
line 55: ‘...crust, geomagnetically induced currents in power lines, railways and pipelines, archeological ...”;
-
lines 82-83: ‘...more observatories, improving their spatial distribution across the planet, providing for better instrumentation, with reduced noise levels, improving temporal and amplitude precision. It requires well-trained personnel, continuity of data, robust...’
-
line 100: Delete ‘modulus’;
-
line 107-112: What about a scalar magnetometer?
-
line 120: ’...The site should exhibit minimal spatial gradients.’
-
lines 164-165: In Figure 1, it would improve clarity to color stars differently from
triangles.
-
lines 175-176: ‘...These should not exceed 1nT/m, at the location of the absolute
measurement instruments, measured with...’
-
lines 187-188: ‘... foundations such as the ???’
-
Section 3: For clarity, the numbering of the study sites should be consistent with Table
1. Accordingly, Section 3.1 should refer to sites # 1-4, Section 3.2 to sites # 5-6, Section
3.3.1 to site # 7, Section 3.3.2 to site # 8, and so on;
-
line 239: Which ‘issues’ were identified?
-
line 245: Reference to Figure 3 appears in the text before Figure 2. This should be corrected.
-
line 246: ‘... presents a contour plot of the magnetic field intensity F from data measured on...’
-
line 247: Elevation contours are not seen in figures 3 or 4. I don’t think they are required, but they are mentioned in the text. Why is it expected a correlation between elevation and F contours? We don’t see such a correlation in Figures 5, 6, 8, 10...
-
line 250: Not clear what is meant by ‘bottom of Figure 3’;
-
lines 259-260: The choice of the exterior site to make a profile seems to have been made based on where internal and external reference points coincide. Please explain the importance of the measurements represented in Figure 2. It is missing information on the magnetic measurements along the mine axis.
-
line 270: Does Figure 3 represent mesh # 3 in Table 2? Please clarify in the legend. Does Figure 4 represent mesh #7? Needs also to be made clear. In Legend of Figure 3, ‘Elevated’ should be ‘Highest’. Note that the ‘background’ value removed is different in Figures 3 and 4. Is this a mistake?
-
line 282: It doesn’t seem necessary to add Table 3, since it has one single row.
-
lines 284-286: Not clear why this site was discarded. Needs a more careful explanation, based on the magnetic measurements that were obtained. What was the altitude of the survey?
-
line 313: Correct to ‘(Table 4: survey Figures 5, 6(a) and 6(b)).’
-
line 313: ‘...anomalies persisted, which were attributed to...’
-
line 319: Figure 5: It is expected that aerial magnetic values are lower than ground values. But why are TOTAL mesh values as low as the aerial values? Also, what is the altitude of the aerial survey? Profile 3 is missing. The mesh polygons are not clearly delineated.
-
line 320: The elevation contours in figures 6a-f, make it difficult to identify clearly the magnetic anomalies. Better figures can be found in the Annexes of the first submitted version of the manuscript (figures 14, 16, 17, 18). Note that although Figures 6b–d cover overlapping regions, the magnetic contours differ significantly. Also, Figure 6f) is the representation of a mesh of points, although it is labeled as representing profiles 11, 12, and 13.
-
lines 342-346: Why is the path of the shown profiles so irregular, and why do magnetic measurements oscillate so much? It is missing a discussion on the obtained results.\
-
lines 355-356: Shouldn’t it be Figures 9 instead of Figures 18?
-
line 358: What does it mean ‘daily prospecting contour plots’?
-
lines 360-362: Figure 9 is missing the location of the best site to install the observatory; profile 19 is also missing; profiles 10a and 10b are missing.
-
lines 362-364: Figure 10: These figures are very rough and need to be worked out. Profiles # 10, 11, and 12 are represented as meshes; there seems to be some mistake.
-
Section 3.9: How is this information related to the installation of a magnetic observatory?
-
line 478: Alexandra Pais did not conceive this project. Please correct.
-
-
RC2: 'Comment on egusphere-2025-2319', Shuaiqing Qiao, 24 Jan 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-2319/egusphere-2025-2319-RC2-supplement.pdf
-
AC4: 'Reply on RC2', Yvelice Castillo, 13 Apr 2026
REPLY TO REFEREE COMMENTS OF 23 JANUARY 2026
The manuscript primarily recounts the extensive work the team conducted in Honduras for electromagnetic detection. It reads more like an engineering report than a research paper.
Reply: In this version, the wording has been revised to make it more suitable for a scientific article.
Regarding the content, the following questions and suggestions are raised:
- The article mentions the team's geomagnetic detection work in Honduras. The obtained geomagnetic data should be analyzed in depth to reveal substantial advantages and compare it with other sites, rather than providing superficial analysis or simply using others' data for explanation.
Reply: A deeper and rigorous analysis of the prospecting data is presented.
- The article devotes considerable space to describing the difficulties and challenges of the work; it is recommended to reduce this section appropriately.
Reply: These arguments were removed.
- What is the magnitude and three components of the geomagnetic intensity at the selected location?
Reply: A definitive site was not presented because we do not have enough information for selecting it. However, thanks to the geology characterization of the sites, it is recommended to do prospecting in the deeper tunnels of the Francisco Morazán dam, due the are located into a limestone formation. There a continuous measurement of the magnetic vector components must be done.
- The key specifications of the equipment selected during the survey should be listed.
Reply: The specification of the magnetometers and other instruments were added.
- If a geomagnetic observatory were to be built at the selected location, what are the plans and arrangements, and what equipment will be deployed?
The donors consulted have stipulated that the facilities must be completed before the equipment is delivered. The equipment in question may vary depending on the donor and the time the facilities will be completed.
Citation: https://doi.org/10.5194/egusphere-2025-2319-AC4
-
AC4: 'Reply on RC2', Yvelice Castillo, 13 Apr 2026
Status: closed
-
AC1: 'Comment on egusphere-2025-2319', Yvelice Castillo, 07 Dec 2025
The authors have made the following corrections at the request of the British Geological Survey staff:
- Minor corrections to the text
- More bibliographic references
- Figure 1 and annexes removed
- Figures 7, 9, and 11 (now 6, 8, and 10) were separated into several contour graphs (one per day) because the surveys were conducted on different dates, diurnal correction was applied, and geomagnetic storms occurred in some cases.
Attached a ZIP file containing the corrected version with figures in PDF format
-
AC2: 'Reply on AC1', Yvelice Castillo, 13 Apr 2026
REPLY TO REFEREE COMMENTS OF 23 JANUARY 2026
The manuscript primarily recounts the extensive work the team conducted in Honduras for electromagnetic detection. It reads more like an engineering report than a research paper.
Reply: In this version, the wording has been revised to make it more suitable for a scientific article.
Regarding the content, the following questions and suggestions are raised:
- The article mentions the team's geomagnetic detection work in Honduras. The obtained geomagnetic data should be analyzed in depth to reveal substantial advantages and compare it with other sites, rather than providing superficial analysis or simply using others' data for explanation.
Reply: A deeper and rigorous analysis of the prospecting data is presented.
- The article devotes considerable space to describing the difficulties and challenges of the work; it is recommended to reduce this section appropriately.
Reply: These arguments were removed.
- What is the magnitude and three components of the geomagnetic intensity at the selected location?
Reply: A definitive site was not presented because we do not have enough information for selecting it. However, thanks to the geology characterization of the sites, it is recommended to do prospecting in the deeper tunnels of the Francisco Morazán dam, due the are located into a limestone formation. There a continuous measurement of the magnetic vector components must be done.
- The key specifications of the equipment selected during the survey should be listed.
Reply: The specification of the magnetometers and other instruments were added.
- If a geomagnetic observatory were to be built at the selected location, what are the plans and arrangements, and what equipment will be deployed?
The donors consulted have stipulated that the facilities must be completed before the equipment is delivered. The equipment in question may vary depending on the donor and the time the facilities will be completed.
REPLY TO REFEREE COMMENTS OF DECEMBER 2025
Global comments
This study reports on an important effort to identify a suitable site for the installation of the first magnetic observatory in Honduras. The relevance of such an infrastructure is clearly explained, as it enables both the monitoring of the secular variation of the Earth’s main magnetic field and the observation of geomagnetic activity associated with interactions with energetic particles from the Sun, which may pose risks to various types of man-made infrastructure.
Due to a range of difficulties encountered throughout the project—such as the need to coordinate with multiple institutions, limited funding for instrumentation, lack of prior experience in this field, the COVID-19 pandemic, and the presence of different sources of perturbations at the tested sites—the project extended over a period of six years.
Although the relevance of this type of study is fully acknowledged, the submitted manuscript largely reads as a report of the work carried out and lacks a deeper and more rigorous analysis of the data acquired during the various surveys. Moreover, even as a report, it lacks clarity in several points, as detailed below.
Reply: In this version, the wording has been revised to make it more suitable for a scientific article. A deeper and rigorous analysis of the prospecting data is presented.
The manuscript also does not lead to a clear final choice for the new magnetic observatory. The apparently best candidate site, Zambrano Mountain, still requires additional testing, particularly with respect to the presence of magnetized rocks, the influence of a nearby power line, and various logistical challenges.
Reply: We realized that more prospecting and testing is needed, and we are proposing to do prospecting at the Francisco Morazán dam deeper tunnels, because they are located inside a limestone formation. Therefore, they would be good candidates to install the magnetic observatory.
In addition, electrical soundings would be required to properly characterize the lateral variability and depth profile of the local ground conductivity.
Reply: We added this at the Recommendations section.
Main issues in the manuscript:
- A geological and lithological characterization of the surveyed region is missing, including an assessment of its tectonic setting. Such information is essential for understanding the distribution of undesirably strong crustal magnetization and for identifying the most suitable locations within limestone terrains.
Reply: The geological characterizations were added to the article.
- We understand that a great effort has been made over six years through multiple surveys. However, the manuscript gives too much emphasis to reporting all the given steps and lacks a more rigorous analysis of data that could yield results of broader interest to other teams facing similar challenges. For instance, in the case of the First Communications Battalion site, a substantial amount of survey data is available (including aerial and ground magnetic profiles as well as mesh surveys), covering an area of approximately 400 × 600 m. Why has no attempt been made to integrate these datasets into a single magnetic anomaly map?
Reply: Anomaly maps were added for data measured during calm days.
- In some cases, a surveyed site is dismissed not on the basis of the magnetic survey data presented in the manuscript, but rather on the basis of other information that is not sufficiently discussed. For example, the rejection of the Mirador mine site appears to rely on the reportedly high humidity levels inside the mine. Were these values compared with those observed at established observatories, such as Conrad Observatory or observatories located in Arctic regions? Similarly, concerns related to the 50 Hz signal from the Francisco Morazan power station are mentioned. Was a variometer operated in a continuous monitoring mode over a sufficiently long period to properly assess this disturbance?
Reply: We added other reasons to explain why the Mirador mine was rejected. First, this area is very popular for hiking; second, the properties are privately owned, not government-owned; third, the equipment that was to be donated would rust easily due to the humidity; fourth, access is somewhat difficult; fifth, there isn’t enough security in the area; and the electrical supply is not easy to install.
In the Recommendations section we added that a continuous measurement of the magnetic components must be done in the selected site (in this case, the deeper tunnel of the Francisco Morazán dam).
- Several of the maps remain insufficiently informative. In particular, contour maps presented in the Appendix of the original submission reveal more clearly the magnetic gradients than the revised figures uploaded on 7 December. In addition, figures using background raster images (Figs. 5, 7, and 9 in version 2) fail to clearly distinguish profiles from meshes, and mix two colour scales, resulting in a confusing visual representation.
Reply: All contour maps and bubble maps were corrected as recommended.
- It is difficult to evaluate distances when using latitude and longitude in the coordinate axis, as is the case in most figures. Better to use meters (m) instead.
Reply: geographical coordinates were substituted by UTM coordinates.
- A diurnal correction is mentioned in the legends of Figures 6 and 8. Which magnetic observatory, or variometer station, was used to this end?
Reply: All data were corrected by diurnal variation using the total magnetic field intensity of the Magnetic Observatory of San Juan, Puerto Rico, with 1 second cadence.
- The ‘Recommendations’ presented in Section 3.11 largely reflect common knowledge within the geomagnetic community and are not directly supported by the findings of this study.
Reply: Recommendations were changed.
- The ‘Conclusions’ in Section 4 focus primarily on the general motivation for this type of study, as introduced earlier in the manuscript, while a clearer link to the specific results of the present work would strengthen this section.
Reply: Conclusions were corrected, based in the analysis of the results.
Specific issues: Note that line and figure numbers below refer to version 2 of the manuscript, uploaded on the 7th December.
- lines 30-31: ‘...guidelines of the ‘Guide for Magnetic Measurements and Observatory Practice’ published by the International ...’; Substituted
- lines 37-41: Text starting at ‘Furthermore, offers of ...’ should be removed from the abstract; Removed
- line 55: ‘...crust, geomagnetically induced currents in power lines, railways and pipelines, archeological ...”; Substituted
- lines 82-83: ‘...more observatories, improving their spatial distribution across the planet, providing for better instrumentation, with reduced noise levels, improving temporal and amplitude precision. It requires well-trained personnel, continuity of data, robust...’ Substituted
- line 100: Delete ‘modulus’; Deleted
- line 107-112: What about a scalar magnetometer? a scalar proton magnetometer…
- line 120: ’...The site should exhibit minimal spatial gradients.’ Substituted
- lines 164-165: In Figure 1, it would improve clarity to color stars differently from
triangles. Colour was added to the stars and triangles.
- lines 175-176: ‘...These should not exceed 1nT/m, at the location of the absolute
measurement instruments, measured with...’ Corrected.
- lines 187-188: ‘... foundations such as the ???’ Amitigra Foundation.
- Section 3: For clarity, the numbering of the study sites should be consistent with Table. Accordingly, Section 3.1 should refer to sites # 1-4, Section 3.2 to sites # 5-6, Section 3.3.1 to site # 7, Section 3.3.2 to site # 8, and so on; Headers and numbering were added to Table, corresponding to section 3 numbering.
- line 239: Which ‘issues’ were identified? First, this area is very popular for hiking; second, the properties are privately owned, not government-owned; third, the equipment that was to be donated would rust easily due to the humidity; fourth, access is somewhat difficult; fifth, there isn’t enough security in the area; and the electrical supply is not easy to install.
- line 245: Reference to Figure 3 appears in the text before Figure 2. This should be corrected. All previous, except Figure 1 were eliminated and substituted by others.
- line 246: ‘... presents a contour plot of the magnetic field intensity F from data measured on...’ Substituted
- line 247: Elevation contours are not seen in figures 3 or 4. I don’t think they are required, but they are mentioned in the text. Why is it expected a correlation between elevation and F contours? We don’t see such a correlation in Figures 5, 6, 8, 10... No elevations were measured for the Figures 3 and 4. Previous referee asked to include the elevations because he says that a correlation exists between the slope angle and the F values.
- line 250: Not clear what is meant by ‘bottom of Figure 3’; This figure was eliminated.
- lines 259-260: The choice of the exterior site to make a profile seems to have been made based on where internal and external reference points coincide. Please explain the importance of the measurements represented in Figure 2. It is missing information on the magnetic measurements along the mine axis. Profiles inside and outside the mine were added as a right panel of Figure 2. This panel shows the magnetic profiles along the main axis (green and black), and an outside profile over the main axis, done with the aid of the total station (see Figure 3). Besides the exterior has large anomalies, the mine’s interior has low magnetic gradients, but its length is only about 70 meters.
- line 270: Does Figure 3 represent mesh # 3 in Table 2? Please clarify in the legend. Corrected. Does Figure 4 represent mesh #7? Corrected. Needs also to be made clear. In Legend of Figure 3, ‘Elevated’ should be ‘Highest’ (substituted). Note that the ‘background’ value removed is different in Figures 3 and 4. Is this a mistake? New background values are 36000 nT.
- line 282: It doesn’t seem necessary to add Table 3, since it has one single row. Table was removed.
- lines 284-286: Not clear why this site was discarded. Needs a more careful explanation, based on the magnetic measurements that were obtained. What was the altitude of the survey? Unfortunately, the drone did not complete its scheduled flight, and the measurements present significant anomalies. Additionally, moderate pedestrian activity was observed during the prospecting (anthropogenic noise).
- line 313: Correct to ‘(Table 4: survey Figures 5, 6(a) and 6(b)).’ (Table 3, Figures 5 and 6)
- line 313: ‘...anomalies persisted, which were attributed to...’ Corrected
- line 319: Figure 5: It is expected that aerial magnetic values are lower than ground values. But why are TOTAL mesh values as low as the aerial values? The TOTAL plot was corrected. It presents lower and larger than the aerial prospecting. Also, what is the altitude of the aerial survey? The aerial survey was performed at just 29 m altitude. Profile 3 is missing. The mesh polygons are not clearly delineated. New plots were done.
- line 320: The elevation contours in figures 6a-f, make it difficult to identify clearly the magnetic anomalies. Better figures can be found in the Annexes of the first submitted version of the manuscript (figures 14, 16, 17, 18). Note that although Figures 6b–d cover overlapping regions, the magnetic contours differ significantly. Also, Figure 6f) is the representation of a mesh of points, although it is labeled as representing profiles 11, 12, and 13. Elevation contours were removed. Diurnal variation correction was done. Magnetic anomalies maps were done.
- lines 342-346: Why is the path of the shown profiles so irregular, and why do magnetic measurements oscillate so much? It is missing a discussion on the obtained results. We had to follow the path because the undergrowth was very thick and access to the mountain was very difficult. The significant anomalies are due to the presence of buried foreign materials left over from the construction of the dam.
- lines 355-356: Shouldn’t it be Figures 9 instead of Figures 18? Corrected
line 358: What does it mean ‘daily prospecting contour plots’? Corrected as plots corrected by daily variation using the total magnetic field intensity of the Magnetic Observatory of San Juan, Puerto Rico. Note in Table 2 that geomagnetic storms occurred during some prospecting.
- lines 360-362: Figure 9 is missing the location of the best site to install the observatory; profile 19 is also missing; profiles 10a and 10b are missing. Figures were corrected and profiles were added.
- lines 362-364: Figure 10: These figures are very rough and need to be worked out. Profiles # 10, 11, and 12 are represented as meshes; there seems to be some mistake. Figures corrected.
- Section 3.9: How is this information related to the installation of a magnetic observatory? This section was removed.
- line 478: Alexandra Pais did not conceive this project. Please correct. Corrected
Citation: https://doi.org/10.5194/egusphere-2025-2319-AC2 -
AC3: 'Reply on AC1', Yvelice Castillo, 13 Apr 2026
REPLY TO REFEREE COMMENTS OF DECEMBER 2025
Global comments
This study reports on an important effort to identify a suitable site for the installation of the first magnetic observatory in Honduras. The relevance of such an infrastructure is clearly explained, as it enables both the monitoring of the secular variation of the Earth’s main magnetic field and the observation of geomagnetic activity associated with interactions with energetic particles from the Sun, which may pose risks to various types of man-made infrastructure.
Due to a range of difficulties encountered throughout the project—such as the need to coordinate with multiple institutions, limited funding for instrumentation, lack of prior experience in this field, the COVID-19 pandemic, and the presence of different sources of perturbations at the tested sites—the project extended over a period of six years.
Although the relevance of this type of study is fully acknowledged, the submitted manuscript largely reads as a report of the work carried out and lacks a deeper and more rigorous analysis of the data acquired during the various surveys. Moreover, even as a report, it lacks clarity in several points, as detailed below.
Reply: In this version, the wording has been revised to make it more suitable for a scientific article. A deeper and rigorous analysis of the prospecting data is presented.
The manuscript also does not lead to a clear final choice for the new magnetic observatory. The apparently best candidate site, Zambrano Mountain, still requires additional testing, particularly with respect to the presence of magnetized rocks, the influence of a nearby power line, and various logistical challenges.
Reply: We realized that more prospecting and testing is needed, and we are proposing to do prospecting at the Francisco Morazán dam deeper tunnels, because they are located inside a limestone formation. Therefore, they would be good candidates to install the magnetic observatory.
In addition, electrical soundings would be required to properly characterize the lateral variability and depth profile of the local ground conductivity.
Reply: We added this at the Recommendations section.
Main issues in the manuscript:
- A geological and lithological characterization of the surveyed region is missing, including an assessment of its tectonic setting. Such information is essential for understanding the distribution of undesirably strong crustal magnetization and for identifying the most suitable locations within limestone terrains.
Reply: The geological characterizations were added to the article.
- We understand that a great effort has been made over six years through multiple surveys. However, the manuscript gives too much emphasis to reporting all the given steps and lacks a more rigorous analysis of data that could yield results of broader interest to other teams facing similar challenges. For instance, in the case of the First Communications Battalion site, a substantial amount of survey data is available (including aerial and ground magnetic profiles as well as mesh surveys), covering an area of approximately 400 × 600 m. Why has no attempt been made to integrate these datasets into a single magnetic anomaly map?
Reply: Anomaly maps were added for data measured during calm days.
- In some cases, a surveyed site is dismissed not on the basis of the magnetic survey data presented in the manuscript, but rather on the basis of other information that is not sufficiently discussed. For example, the rejection of the Mirador mine site appears to rely on the reportedly high humidity levels inside the mine. Were these values compared with those observed at established observatories, such as Conrad Observatory or observatories located in Arctic regions? Similarly, concerns related to the 50 Hz signal from the Francisco Morazan power station are mentioned. Was a variometer operated in a continuous monitoring mode over a sufficiently long period to properly assess this disturbance?
Reply: We added other reasons to explain why the Mirador mine was rejected. First, this area is very popular for hiking; second, the properties are privately owned, not government-owned; third, the equipment that was to be donated would rust easily due to the humidity; fourth, access is somewhat difficult; fifth, there isn’t enough security in the area; and the electrical supply is not easy to install.
In the Recommendations section we added that a continuous measurement of the magnetic components must be done in the selected site (in this case, the deeper tunnel of the Francisco Morazán dam).
- Several of the maps remain insufficiently informative. In particular, contour maps presented in the Appendix of the original submission reveal more clearly the magnetic gradients than the revised figures uploaded on 7 December. In addition, figures using background raster images (Figs. 5, 7, and 9 in version 2) fail to clearly distinguish profiles from meshes, and mix two colour scales, resulting in a confusing visual representation.
Reply: All contour maps and bubble maps were corrected as recommended.
- It is difficult to evaluate distances when using latitude and longitude in the coordinate axis, as is the case in most figures. Better to use meters (m) instead.
Reply: geographical coordinates were substituted by UTM coordinates.
- A diurnal correction is mentioned in the legends of Figures 6 and 8. Which magnetic observatory, or variometer station, was used to this end?
Reply: All data were corrected by diurnal variation using the total magnetic field intensity of the Magnetic Observatory of San Juan, Puerto Rico, with 1 second cadence.
- The ‘Recommendations’ presented in Section 3.11 largely reflect common knowledge within the geomagnetic community and are not directly supported by the findings of this study.
Reply: Recommendations were changed.
- The ‘Conclusions’ in Section 4 focus primarily on the general motivation for this type of study, as introduced earlier in the manuscript, while a clearer link to the specific results of the present work would strengthen this section.
Reply: Conclusions were corrected, based in the analysis of the results.
Specific issues: Note that line and figure numbers below refer to version 2 of the manuscript, uploaded on the 7th December.
- lines 30-31: ‘...guidelines of the ‘Guide for Magnetic Measurements and Observatory Practice’ published by the International ...’; Substituted
- lines 37-41: Text starting at ‘Furthermore, offers of ...’ should be removed from the abstract; Removed
- line 55: ‘...crust, geomagnetically induced currents in power lines, railways and pipelines, archeological ...”; Substituted
- lines 82-83: ‘...more observatories, improving their spatial distribution across the planet, providing for better instrumentation, with reduced noise levels, improving temporal and amplitude precision. It requires well-trained personnel, continuity of data, robust...’ Substituted
- line 100: Delete ‘modulus’; Deleted
- line 107-112: What about a scalar magnetometer? a scalar proton magnetometer…
- line 120: ’...The site should exhibit minimal spatial gradients.’ Substituted
- lines 164-165: In Figure 1, it would improve clarity to color stars differently from
triangles. Colour was added to the stars and triangles.
- lines 175-176: ‘...These should not exceed 1nT/m, at the location of the absolute
measurement instruments, measured with...’ Corrected.
- lines 187-188: ‘... foundations such as the ???’ Amitigra Foundation.
- Section 3: For clarity, the numbering of the study sites should be consistent with Table. Accordingly, Section 3.1 should refer to sites # 1-4, Section 3.2 to sites # 5-6, Section 3.3.1 to site # 7, Section 3.3.2 to site # 8, and so on; Headers and numbering were added to Table, corresponding to section 3 numbering.
- line 239: Which ‘issues’ were identified? First, this area is very popular for hiking; second, the properties are privately owned, not government-owned; third, the equipment that was to be donated would rust easily due to the humidity; fourth, access is somewhat difficult; fifth, there isn’t enough security in the area; and the electrical supply is not easy to install.
- line 245: Reference to Figure 3 appears in the text before Figure 2. This should be corrected. All previous, except Figure 1 were eliminated and substituted by others.
- line 246: ‘... presents a contour plot of the magnetic field intensity F from data measured on...’ Substituted
- line 247: Elevation contours are not seen in figures 3 or 4. I don’t think they are required, but they are mentioned in the text. Why is it expected a correlation between elevation and F contours? We don’t see such a correlation in Figures 5, 6, 8, 10... No elevations were measured for the Figures 3 and 4. Previous referee asked to include the elevations because he says that a correlation exists between the slope angle and the F values.
- line 250: Not clear what is meant by ‘bottom of Figure 3’; This figure was eliminated.
- lines 259-260: The choice of the exterior site to make a profile seems to have been made based on where internal and external reference points coincide. Please explain the importance of the measurements represented in Figure 2. It is missing information on the magnetic measurements along the mine axis. Profiles inside and outside the mine were added as a right panel of Figure 2. This panel shows the magnetic profiles along the main axis (green and black), and an outside profile over the main axis, done with the aid of the total station (see Figure 3). Besides the exterior has large anomalies, the mine’s interior has low magnetic gradients, but its length is only about 70 meters.
- line 270: Does Figure 3 represent mesh # 3 in Table 2? Please clarify in the legend. Corrected. Does Figure 4 represent mesh #7? Corrected. Needs also to be made clear. In Legend of Figure 3, ‘Elevated’ should be ‘Highest’ (substituted). Note that the ‘background’ value removed is different in Figures 3 and 4. Is this a mistake? New background values are 36000 nT.
- line 282: It doesn’t seem necessary to add Table 3, since it has one single row. Table was removed.
- lines 284-286: Not clear why this site was discarded. Needs a more careful explanation, based on the magnetic measurements that were obtained. What was the altitude of the survey? Unfortunately, the drone did not complete its scheduled flight, and the measurements present significant anomalies. Additionally, moderate pedestrian activity was observed during the prospecting (anthropogenic noise).
- line 313: Correct to ‘(Table 4: survey Figures 5, 6(a) and 6(b)).’ (Table 3, Figures 5 and 6)
- line 313: ‘...anomalies persisted, which were attributed to...’ Corrected
- line 319: Figure 5: It is expected that aerial magnetic values are lower than ground values. But why are TOTAL mesh values as low as the aerial values? The TOTAL plot was corrected. It presents lower and larger than the aerial prospecting. Also, what is the altitude of the aerial survey? The aerial survey was performed at just 29 m altitude. Profile 3 is missing. The mesh polygons are not clearly delineated. New plots were done.
- line 320: The elevation contours in figures 6a-f, make it difficult to identify clearly the magnetic anomalies. Better figures can be found in the Annexes of the first submitted version of the manuscript (figures 14, 16, 17, 18). Note that although Figures 6b–d cover overlapping regions, the magnetic contours differ significantly. Also, Figure 6f) is the representation of a mesh of points, although it is labeled as representing profiles 11, 12, and 13. Elevation contours were removed. Diurnal variation correction was done. Magnetic anomalies maps were done.
- lines 342-346: Why is the path of the shown profiles so irregular, and why do magnetic measurements oscillate so much? It is missing a discussion on the obtained results. We had to follow the path because the undergrowth was very thick and access to the mountain was very difficult. The significant anomalies are due to the presence of buried foreign materials left over from the construction of the dam.
- lines 355-356: Shouldn’t it be Figures 9 instead of Figures 18? Corrected
line 358: What does it mean ‘daily prospecting contour plots’? Corrected as plots corrected by daily variation using the total magnetic field intensity of the Magnetic Observatory of San Juan, Puerto Rico. Note in Table 2 that geomagnetic storms occurred during some prospecting.
- lines 360-362: Figure 9 is missing the location of the best site to install the observatory; profile 19 is also missing; profiles 10a and 10b are missing. Figures were corrected and profiles were added.
- lines 362-364: Figure 10: These figures are very rough and need to be worked out. Profiles # 10, 11, and 12 are represented as meshes; there seems to be some mistake. Figures corrected.
- Section 3.9: How is this information related to the installation of a magnetic observatory? This section was removed.
- line 478: Alexandra Pais did not conceive this project. Please correct. Corrected
Citation: https://doi.org/10.5194/egusphere-2025-2319-AC3
-
RC1: 'Comment on egusphere-2025-2319', Anonymous Referee #1, 02 Jan 2026
Global comments
This study reports on an important effort to identify a suitable site for the installation of the first magnetic observatory in Honduras. The relevance of such an infrastructure is clearly explained, as it enables both the monitoring of the secular variation of the Earth’s main magnetic field and the observation of geomagnetic activity associated with interactions with energetic particles from the Sun, which may pose risks to various types of man-made infrastructure.
Due to a range of difficulties encountered throughout the project—such as the need to coor- dinate with multiple institutions, limited funding for instrumentation, lack of prior experience in this field, the COVID-19 pandemic, and the presence of different sources of perturbations at the tested sites—the project extended over a period of six years.
Although the relevance of this type of study is fully acknowledged, the submitted manuscript largely reads as a report of the work carried out and lacks a deeper and more rigorous analysis of the data acquired during the various surveys. Moreover, even as a report, it lacks clarity in several points, as detailed below.
The manuscript also does not lead to a clear final choice for the new magnetic observatory. The apparently best candidate site, Zambrano Mountain, still requires additional testing, par- ticularly with respect to the presence of magnetized rocks, the influence of a nearby power line, and various logistical challenges. In addition, electrical soundings would be required to properly characterize the lateral variability and depth profile of the local ground conductivity.
Main issues in the manuscript:
-
A geological and lithological characterization of the surveyed region is missing, including an assessment of its tectonic setting. Such information is essential for understanding the distribution of undesirably strong crustal magnetization and for identifying the most suitable locations within limestone terrains.
-
We understand that a great effort has been made over six years through multiple surveys. However, the manuscript gives too much emphasis to reporting all the given steps and lacks a more rigorous analysis of data that could yield results of broader interest to other teams facing similar challenges. For instance, in the case of the First Communications Battalion site, a substantial amount of survey data is available (including aerial and ground magnetic profiles as well as mesh surveys), covering an area of approximately 400 × 600 m. Why has no attempt been made to integrate these datasets into a single magnetic anomaly map?
-
In some cases, a surveyed site is dismissed not on the basis of the magnetic survey data presented in the manuscript, but rather on the basis of other information that is not sufficiently discussed. For example, the rejection of the Mirador mine site appears to rely on the reportedly high humidity levels inside the mine. Were these values compared with those observed at established observatories, such as Conrad Observatory or observatories located in Arctic regions? Similarly, concerns related to the 50 Hz signal from the Francisco Moraz ́an power station are mentioned. Was a variometer operated in a continuous monitoring mode over a sufficiently long period to properly assess this disturbance?
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Several of the maps remain insufficiently informative. In particular, contour maps presented in the Appendix of the original submission reveal more clearly the magnetic gradients than the revised figures uploaded on 7 December. In addition, figures using background raster images (Figs. 5, 7, and 9 in version 2) fail to clearly distinguish profiles from meshes, and mix two colour scales, resulting in a confusing visual representation.
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It is difficult to evaluate distances when using latitude and longitude in the coordinate axis, as is the case in most figures. Better to use meters (m) instead.
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A diurnal correction is mentioned in the legends of Figures 6 and 8. Which magnetic observatory, or variometer station, was used to this end?
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The ‘Recommendations’ presented in Section 3.11 largely reflect common knowledge within the geomagnetic community and are not directly supported by the findings of this study.
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The ‘Conclusions’ in Section 4 focus primarily on the general motivation for this type of study, as introduced earlier in the manuscript, while a clearer link to the specific results of the present work would strengthen this section.
Specific issues: Note that line and figure numbers below refer to version 2 of the manuscript, uploaded on the 7th December.
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lines 30-31: ‘...guidelines of the ‘Guide for Magnetic Measurements and Observatory Practice’ published by the International ...’;
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lines 37-41: Text starting at ‘Furthermore, offers of ...’ should be removed from the abstract;
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line 55: ‘...crust, geomagnetically induced currents in power lines, railways and pipelines, archeological ...”;
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lines 82-83: ‘...more observatories, improving their spatial distribution across the planet, providing for better instrumentation, with reduced noise levels, improving temporal and amplitude precision. It requires well-trained personnel, continuity of data, robust...’
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line 100: Delete ‘modulus’;
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line 107-112: What about a scalar magnetometer?
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line 120: ’...The site should exhibit minimal spatial gradients.’
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lines 164-165: In Figure 1, it would improve clarity to color stars differently from
triangles.
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lines 175-176: ‘...These should not exceed 1nT/m, at the location of the absolute
measurement instruments, measured with...’
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lines 187-188: ‘... foundations such as the ???’
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Section 3: For clarity, the numbering of the study sites should be consistent with Table
1. Accordingly, Section 3.1 should refer to sites # 1-4, Section 3.2 to sites # 5-6, Section
3.3.1 to site # 7, Section 3.3.2 to site # 8, and so on;
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line 239: Which ‘issues’ were identified?
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line 245: Reference to Figure 3 appears in the text before Figure 2. This should be corrected.
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line 246: ‘... presents a contour plot of the magnetic field intensity F from data measured on...’
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line 247: Elevation contours are not seen in figures 3 or 4. I don’t think they are required, but they are mentioned in the text. Why is it expected a correlation between elevation and F contours? We don’t see such a correlation in Figures 5, 6, 8, 10...
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line 250: Not clear what is meant by ‘bottom of Figure 3’;
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lines 259-260: The choice of the exterior site to make a profile seems to have been made based on where internal and external reference points coincide. Please explain the importance of the measurements represented in Figure 2. It is missing information on the magnetic measurements along the mine axis.
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line 270: Does Figure 3 represent mesh # 3 in Table 2? Please clarify in the legend. Does Figure 4 represent mesh #7? Needs also to be made clear. In Legend of Figure 3, ‘Elevated’ should be ‘Highest’. Note that the ‘background’ value removed is different in Figures 3 and 4. Is this a mistake?
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line 282: It doesn’t seem necessary to add Table 3, since it has one single row.
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lines 284-286: Not clear why this site was discarded. Needs a more careful explanation, based on the magnetic measurements that were obtained. What was the altitude of the survey?
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line 313: Correct to ‘(Table 4: survey Figures 5, 6(a) and 6(b)).’
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line 313: ‘...anomalies persisted, which were attributed to...’
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line 319: Figure 5: It is expected that aerial magnetic values are lower than ground values. But why are TOTAL mesh values as low as the aerial values? Also, what is the altitude of the aerial survey? Profile 3 is missing. The mesh polygons are not clearly delineated.
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line 320: The elevation contours in figures 6a-f, make it difficult to identify clearly the magnetic anomalies. Better figures can be found in the Annexes of the first submitted version of the manuscript (figures 14, 16, 17, 18). Note that although Figures 6b–d cover overlapping regions, the magnetic contours differ significantly. Also, Figure 6f) is the representation of a mesh of points, although it is labeled as representing profiles 11, 12, and 13.
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lines 342-346: Why is the path of the shown profiles so irregular, and why do magnetic measurements oscillate so much? It is missing a discussion on the obtained results.\
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lines 355-356: Shouldn’t it be Figures 9 instead of Figures 18?
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line 358: What does it mean ‘daily prospecting contour plots’?
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lines 360-362: Figure 9 is missing the location of the best site to install the observatory; profile 19 is also missing; profiles 10a and 10b are missing.
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lines 362-364: Figure 10: These figures are very rough and need to be worked out. Profiles # 10, 11, and 12 are represented as meshes; there seems to be some mistake.
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Section 3.9: How is this information related to the installation of a magnetic observatory?
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line 478: Alexandra Pais did not conceive this project. Please correct.
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RC2: 'Comment on egusphere-2025-2319', Shuaiqing Qiao, 24 Jan 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-2319/egusphere-2025-2319-RC2-supplement.pdf
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AC4: 'Reply on RC2', Yvelice Castillo, 13 Apr 2026
REPLY TO REFEREE COMMENTS OF 23 JANUARY 2026
The manuscript primarily recounts the extensive work the team conducted in Honduras for electromagnetic detection. It reads more like an engineering report than a research paper.
Reply: In this version, the wording has been revised to make it more suitable for a scientific article.
Regarding the content, the following questions and suggestions are raised:
- The article mentions the team's geomagnetic detection work in Honduras. The obtained geomagnetic data should be analyzed in depth to reveal substantial advantages and compare it with other sites, rather than providing superficial analysis or simply using others' data for explanation.
Reply: A deeper and rigorous analysis of the prospecting data is presented.
- The article devotes considerable space to describing the difficulties and challenges of the work; it is recommended to reduce this section appropriately.
Reply: These arguments were removed.
- What is the magnitude and three components of the geomagnetic intensity at the selected location?
Reply: A definitive site was not presented because we do not have enough information for selecting it. However, thanks to the geology characterization of the sites, it is recommended to do prospecting in the deeper tunnels of the Francisco Morazán dam, due the are located into a limestone formation. There a continuous measurement of the magnetic vector components must be done.
- The key specifications of the equipment selected during the survey should be listed.
Reply: The specification of the magnetometers and other instruments were added.
- If a geomagnetic observatory were to be built at the selected location, what are the plans and arrangements, and what equipment will be deployed?
The donors consulted have stipulated that the facilities must be completed before the equipment is delivered. The equipment in question may vary depending on the donor and the time the facilities will be completed.
Citation: https://doi.org/10.5194/egusphere-2025-2319-AC4
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AC4: 'Reply on RC2', Yvelice Castillo, 13 Apr 2026
Data sets
The Honduras' “La Tigra” National Park ground geomagnetic prospecting, July -- November 2019 Yvelice Castillo, Manuel Rodríguez, Norman Palma, and Félix Rodríguez http://dx.doi.org/10.13140/RG.2.2.31366.43848
The Honduras Army's First Communications Battalion ground geomagnetic prospecting on April 2022 Yvelice Castillo, Manuel Rodríguez, Norman Palma, and Félix Rodríguez http://dx.doi.org/10.13140/RG.2.2.15847.51366
The Honduras Army's First-Communications-Battalion's Aerial Prospecting on June 2022 Yvelice Castillo, Manuel Rodríguez, Norman Palma, and Félix Rodríguez http://dx.doi.org/10.13140/RG.2.2.12701.78569
The Honduras' “Francisco Morazán” Power Station ground geomagnetic prospecting, November 2024 Yvelice Castillo and Norman Palma http://dx.doi.org/10.13140/RG.2.2.15218.36802
The Honduras Army's First Communications Battalion ground geomagnetic prospecting, August -- November 2024 Yvelice Castillo, Manuel Rodríguez, Norman Palma, and Félix Rodríguez http://dx.doi.org/10.13140/RG.2.2.26903.43685
The Honduras' “La Tigra” National Park ground geomagnetic prospecting, July -- November 2019 Yvelice Castillo, Manuel Rodríguez, Norman Palma, and Félix Rodríguez http://dx.doi.org/10.13140/RG.2.2.31366.43848
The Honduras Army's First Communications Battalion ground geomagnetic prospecting on April 2022 Yvelice Castillo, Manuel Rodríguez, Norman Palma, and Félix Rodríguez http://dx.doi.org/10.13140/RG.2.2.15847.51366
The Honduras Army's First-Communications-Battalion's Aerial Prospecting on June 2022 Yvelice Castillo, Manuel Rodríguez, Norman Palma, and Félix Rodríguez http://dx.doi.org/10.13140/RG.2.2.12701.78569
The Honduras' “Francisco Morazán” Power Station ground geomagnetic prospecting, November 2024 Yvelice Castillo and Norman Palma http://dx.doi.org/10.13140/RG.2.2.15218.36802
The Honduras Army's First Communications Battalion ground geomagnetic prospecting, August -- November 2024 Yvelice Castillo, Manuel Rodríguez, Norman Palma, and Félix Rodríguez http://dx.doi.org/10.13140/RG.2.2.26903.43685
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The authors have made the following corrections at the request of the British Geological Survey staff:
Attached a ZIP file containing the corrected version with figures in PDF format