the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Dec 2024
New Radar Altimetry Datasets of Greenland and Antarctic Surface Elevation, 1991–2012
Abstract. Over the past three decades, there has been a 4.5-fold increase in the loss of ice from the Greenland and Antarctic Ice Sheets, resulting in an enhanced contribution to global sea level rise. Accurately tracking these changes in ice mass requires comprehensive, long-term measurements, which are only feasible from space. Satellite radar altimetry provides the longest near-continuous record of ice sheet surface elevation and volume change, dating back to the launch of ERS-1 in 1991, and maintained through the successive ERS-2, Envisat, CryoSat-2 and Sentinel-3 missions. To reliably constrain multi-decadal trends in ice sheet imbalance, and to place current observations within a longer-term context, requires continued efforts to optimise the processing of data acquired by the older historical missions, and to evaluate the accuracy of these measurements. Here, we present new ERS-1, ERS-2 and Envisat altimeter datasets, which are derived using consistent and improved retrieval methods, and provide measurements of ice sheet elevation spanning two decades. Through comparison with independent airborne datasets, we provide a comprehensive assessment of the accuracy of these measurements, and the improvements delivered relative to previously available products. These new datasets will be of benefit to a broad range of applications, including the quantification of ice sheet mass imbalance, investigations of the processes driving contemporary ice loss, and the constraint of numerical ice sheet models.
-
Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
-
Preprint
(13909 KB)
-
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(13909 KB) - Metadata XML
- BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-3446', Anonymous Referee #1, 17 Jan 2025
The manuscript reports the generation and assessment of new data products of Greenland Ice Sheet and Antarctic Ice Sheet surface elevation from the ERS-1, ERS-2 and Envisat radar altimetry missions. The underlying reprocessing has been performed within ESA's Fundamental Data Records for Altimetry (FDR4ALT) project. It is to supersede the previous REprocessing Altimeter Products for ERS-2 and ERS-2 (REAPER) and the version 3 products for Envisat.
The data products are on the Level-2 level and contain position and surface elevation along track of satellite measurements. In addition a Thematic Data Product (TDP) is provided (which could be classified as Level-2b). It refers all measurements to reference ground tracks and thereby corrects for the non-exact-repeat nature of the orbits and measurements and for the associated topography-induced variations. I expect that this will largely facilitate higher-level analyses for temporal surface elevation change.The improvements in the processing methodology include up-to-data retracking methods and the Roemer et al. 2007 approach of accounting for local topography by relocation.
The new data products, as well as the previous REAPER and Envisat version 3 products are extensively assessed and validated. Comparison to independent surface elevation data from Operatoin ICEBridge is done for Greenland. For both ice sheets, and for the three missions, waveforms are classified (using 21 different classes) through a Neural Network classification. The geographic distribution and histograms of the waveform classes are shown. For Greenland, this allows to assess surface elevation accuracy per waveform class, with very interesting insights and hints to future work on the waveform classes associated with low accuracy. It is shown convincingly that the new products outperform the previous products in virtually all aspects considered.
I enjoyed reading this manuscript. It is extremely clear and informative, starting with the helpful and succinct summary of the three missions in Section 2.1.-2.3 through the illustration on how the TMP simplifies variability in Section 3.4. Thank you for making the review work so easy.
I only have a few minor-to-moderate comments on how the presentation could be further improved.
From the abstract and even from the introduction it is not clear what kind of dataset is presented. For example, readers of a certain background might expect a gridded data product. So you might specify that it is a Level-2 dataset comprising horizontal coordinates (lat lon, or some projection?) and surface elevation (ellipsoidal heights?) sampled along the satellite track.
The manuscript presents datasets (rather than cryospheric science results). Therefore it would be really appropriate to provide public access to the datasets at the time of publishing the paper, at latest. Currently, the manuscript does not comply with TC data policy (https://www.the-cryosphere.net/policies/data_policy.html)
One might even argue that a data journal like ESSD might be more appropriate for this work. Anyway, I would not mind to see this work published in "The Cryosphere" because the excellent analysis of the data (such as the dependence of accuracy on slope and waveform classes) really facilitates understanding the nature of altimetric surface elevation measurements. And this is the basis for a lot of science.
On a similar line, the reader is referred to technical documents for details of the processing (The FDR4ALT Detailed Processing Model Document; the FDR4ALT Product User Guide), which are currently available at websites. It would be desirable to see some commitment for their persistent availability. (It's also curious that these documents have "confidential" at the bottom of every page.)
I'm not going to insist on this comment, though, as I understand it may not be trivial.The abstract could be a bit more specific as to what kind of improvements have been implemented in the processing and what improvements could be achieved w.r.t. previous datasets.
Concerning the validation by ICEBridge data, the reader might wonder why this exercise was restricted to Greenland. Maybe you can explain or justify this limitation in a sentence or two.
line 84 "had the impact of" --> "had the effect of"
line 704 something wrong about this reference "Team, I"
line 702 same problemIn the disucssion of the relocation you might mention that the geographic position assigned to the measurement is corrected together with the height. This is (of course) not reflected in Eq. 1.
line 187: As fas as I understand, the ocean tide and inverse barometer effect are zero over ice sheets. This could be mentioned for completeness.
289 "mean square error". Maybe "mean square difference" might be a more appropriate term.
line 292ff: The reader learns that this classification was performed for waveforms from not only over the ice sheet.
Make sure in the text that the reader understands which steps are done for global altimetry data and which steps are done specifically for ice sheets.line 345 "less continuous along-track sampling"
I think you could sell this point more positively and avoid the impression (at first reading of this sentence) that this is some disadvantage.line 374 replace "Threshold Centre of Gravity" by TCOG for consistency and brevity.
Fig. 6: This is a great visualisation. Just the histogram insets are too small to be well readable, at least in a printed version. You may try to make them a bit bigger. And convince the journal in the layout process to use the full paper width for the figure. In turn you might cut the headline "Envisat | cycle 78" and put this information into the figure description.
Somehow, Figure 10 is missing completely.
Fig. 12a: It appears that slopes are shown not only for the ice sheet area, which is inconsistent with what is sayed in the figure caption and with the other figures in the manuscript.
line 490f "Comparing performance across the three missions shows an apparent lower accuracy of Envisat at higher slopes, which is likely to
reflect the increased coverage that Envisat achieves in these regions (Figure 5)."
I suggest to replace "Comparing performance" by "Comparing the performance of FDR4ALT" in order to be cristal-clear.
I suggest the reference to Fig. 5 should be replaced by a reference to Table 7, because the increased coverage cannot easily seen from Fig. 5, while it is clearly quantified in Table 7Fig. 12 caption: I suggest to shorten the description by writing something like:
"d and e: same as b and c, but for ERS-2. f and g: same as b and c, but for Envisat"Fig 13 and 14. The caption says "The spatial distribution of the five most common waveform classes". However it seems that not only the five most common classes are depicted. For example, panel a and b show a lot of orange dots, too.
Also, the the color bar is somewhat ambiguous in assigning colors to waveform classes. (Maybe stretch it from -0.5 to 20.5, then the ticks at 0, 1, ..., 20 are in the centre of their color block)
Congratulations for Figure 15. I like your graphical indication of waveform classes at the top of the figure!
Yet I have some minor comments on this figure.
- Choose one name for class 9: either "very complex echo" (as in Tab. 2, 8, 9) or "unclassified" as in the top of Fig. 15.
- There is maybe too much graphical emphasis on the outliers. - certainly a matter of taste.
- Figure 15 caption, last sentence: I guess the order must be changed into "Classes 8, 12, 14, 19-20 and 10, 13-15, 17-20" to match the order "ERS and Envisat"Throughout the paper, be consistent in writing Envisat (rather than ENVISAT)
line 534ff "In contrast, relatively specular (classes 2 and 4) and multipeaked (class 3) waveforms generally produce a negative elevation bias, although the degradation in performance is less severe for Envisat than the preceding missions."
The second half of this sentence is substantiated for class 3 but not for classes 2 and 4. Maybe limit this consideration to class 3, as occurance of class 2 and 4 is rare.line 539 "For Envisat, beyond classes 1, 3 and 7, the most common remaining classes are 9 (very complex) and 11 (stepped leading edge)."
This sentence seems to suggest that classes 9 and 11 are less common than classes 1, 3, 7, but this is not the case.Fig. 16 caption: in line 571, "(row 1)" does not appear to make sense to me.
Citation: https://doi.org/10.5194/egusphere-2024-3446-RC1 -
AC1: 'Reply on RC1', Maya Suryawanshi, 14 Mar 2025
We thank the reviewer for their comments. We address each of the points raised below, with our response provided after each comment.
Initial summary comment: The manuscript reports the generation and assessment of new data products of Greenland Ice Sheet and Antarctic Ice Sheet surface elevation from the ERS-1, ERS-2 and Envisat radar altimetry missions. The underlying reprocessing has been performed within ESA's Fundamental Data Records for Altimetry (FDR4ALT) project. It is to supersede the previous REprocessing Altimeter Products for ERS-2 and ERS-2 (REAPER) and the version 3 products for Envisat.
The data products are on the Level-2 level and contain position and surface elevation along track of satellite measurements. In addition a Thematic Data Product (TDP) is provided (which could be classified as Level-2b). It refers all measurements to reference ground tracks and thereby corrects for the non-exact-repeat nature of the orbits and measurements and for the associated topography-induced variations. I expect that this will largely facilitate higher-level analyses for temporal surface elevation change.
The improvements in the processing methodology include up-to-data retracking methods and the Roemer et al. 2007 approach of accounting for local topography by relocation.
The new data products, as well as the previous REAPER and Envisat version 3 products are extensively assessed and validated. Comparison to independent surface elevation data from Operatoin ICEBridge is done for Greenland. For both ice sheets, and for the three missions, waveforms are classified (using 21 different classes) through a Neural Network classification. The geographic distribution and histograms of the waveform classes are shown. For Greenland, this allows to assess surface elevation accuracy per waveform class, with very interesting insights and hints to future work on the waveform classes associated with low accuracy. It is shown convincingly that the new products outperform the previous products in virtually all aspects considered.
I enjoyed reading this manuscript. It is extremely clear and informative, starting with the helpful and succinct summary of the three missions in Section 2.1.-2.3 through the illustration on how the TMP simplifies variability in Section 3.4. Thank you for making the review work so easy.
Response: Thank you for these comments, we appreciate your recognition of the care we put into preparing the manuscript.
I only have a few minor-to-moderate comments on how the presentation could be further improved.
Comment 1: From the abstract and even from the introduction it is not clear what kind of dataset is presented. For example, readers of a certain background might expect a gridded data product. So you might specify that it is a Level-2 dataset comprising horizontal coordinates (lat lon, or some projection?) and surface elevation (ellipsoidal heights?) sampled along the satellite track.
Response 1: We acknowledge that this was not sufficiently clear, and we will add these details as requested.
Comment 2: The manuscript presents datasets (rather than cryospheric science results). Therefore, it would be really appropriate to provide public access to the datasets at the time of publishing the paper, at latest. Currently, the manuscript does not comply with TC data policy (https://www.the-cryosphere.net/policies/data_policy.html). One might even argue that a data journal like ESSD might be more appropriate for this work. Anyway, I would not mind to see this work published in "The Cryosphere" because the excellent analysis of the data (such as the dependence of accuracy on slope and waveform classes) really facilitates understanding the nature of altimetric surface elevation measurements. And this is the basis for a lot of science.
Response 2: We agree, and can confirm that the data are now publicly available and distributed by ESA. Further details on how to access the data can be found at https://earth.esa.int/eogateway/catalog/tdp-for-land-ice. We will update the manuscript to make this clear. Regarding our wish to publish this work in The Cryosphere rather than ESSD, we agree that in principle it would be in scope for both journals. At the stage of initial submission, we discussed this amongst all coauthors, and decided that we preferred to submit to the former. At this stage, we would like to continue along this route, and so we are happy that the reviewer appreciates the appropriateness of this approach.
Comment 3: On a similar line, the reader is referred to technical documents for details of the processing (The FDR4ALT Detailed Processing Model Document; the FDR4ALT Product User Guide), which are currently available at websites. It would be desirable to see some commitment for their persistent availability. (It's also curious that these documents have "confidential" at the bottom of every page.) I'm not going to insist on this comment, though, as I understand it may not be trivial.
Response 3: These documents are currently hosted by ESA, due to their funding of the work. As part of our revisions, we will explore with them what commitment they can provide in terms of persistence.
Comment 4: The abstract could be a bit more specific as to what kind of improvements have been implemented in the processing and what improvements could be achieved w.r.t. previous datasets.
Response 4: As requested, we will revise the abstract to include these specifics.
Comment 5: Concerning the validation by ICEBridge data, the reader might wonder why this exercise was restricted to Greenland. Maybe you can explain or justify this limitation in a sentence or two.
Response 5: As requested, we will add additional details to explain the justification for this approach. We selected Greenland for validation purposes because (1) it provided the most extensive coverage of validation data for all missions, most notably for pre-IceBridge campaigns where coverage over Antarctica is extremely limited, and (2) it encompassed a broad range of topographic complexity and surface characteristics. We believe that in doing so, our analysis provides a relatively comprehensive assessment of data accuracy, and advances beyond previous work.
Comment 6: line 84 "had the impact of" --> "had the effect of"
Response 6: Agreed; we will update the manuscript as suggested.
Comment 7: line 704 something wrong about this reference "Team, I"
Response 7: Agreed; we will correct this.
Comment 8: line 702 same problem
Response 8: Agreed; we will correct this.
Comment 9: In the discussion of the relocation you might mention that the geographic position assigned to the measurement is corrected together with the height. This is (of course) not reflected in Eq. 1.
Response 9: We will mention this as requested.
Comment 10: line 187: As fas as I understand, the ocean tide and inverse barometer effect are zero over ice sheets. This could be mentioned for completeness.
Response 10: Yes this is correct; we will add text to mention this as requested.
Comment 11: 289 "mean square error". Maybe "mean square difference" might be a more appropriate term.
Response 11: Agreed; we will change this as suggested.
.
Comment 12: line 292ff: The reader learns that this classification was performed for waveforms from not only over the ice sheet.
Response 12: Yes this is correct.
Comment 13: Make sure in the text that the reader understands which steps are done for global altimetry data and which steps are done specifically for ice sheets.
Response 13: As requested, we will make sure it is clear which steps have been performed for global altimetry data.
Comment 14: line 345 "less continuous along-track sampling". I think you could sell this point more positively and avoid the impression (at first reading of this sentence) that this is some disadvantage.
Response 14: As suggested, we will reword this more positively.
Comment 15: line 374 replace "Threshold Centre of Gravity" by TCOG for consistency and brevity.
Response 15: Agreed; we will change this as suggested.
Comment 16: Fig. 6: This is a great visualisation. Just the histogram insets are too small to be well readable, at least in a printed version. You may try to make them a bit bigger. And convince the journal in the layout process to use the full paper width for the figure. In turn you might cut the headline "Envisat | cycle 78" and put this information into the figure description.
Response 16: We will look to modify the layout of this figure to address the point raised.
Comment 17: Somehow, Figure 10 is missing completely.
Response 17: We apologise for this omission and we will add the figure in the revised version.
Comment 18: Fig. 12a: It appears that slopes are shown not only for the ice sheet area, which is inconsistent with what is sayed in the figure caption and with the other figures in the manuscript.
Response 18: We will update the figure to ensure that it only shows surface slope for the ice sheet itself.
Comment 19: line 490f "Comparing performance across the three missions shows an apparent lower accuracy of Envisat at higher slopes, which is likely to reflect the increased coverage that Envisat achieves in these regions (Figure 5)." I suggest to replace "Comparing performance" by "Comparing the performance of FDR4ALT" in order to be cristal-clear.
Response 19: Agreed; we will update the manuscript to reflect this suggestion.
Comment 20: I suggest the reference to Fig. 5 should be replaced by a reference to Table 7, because the increased coverage cannot easily seen from Fig. 5, while it is clearly quantified in Table 7
Response 20: Agreed; we will replace the reference to Fig. 5 with a reference to Table 7.
Comment 21: Fig. 12 caption: I suggest to shorten the description by writing something like:
"d and e: same as b and c, but for ERS-2. f and g: same as b and c, but for Envisat"
Response 21: We will shorten the caption, as suggested.
Comment 22: Fig 13 and 14. The caption says "The spatial distribution of the five most common waveform classes". However it seems that not only the five most common classes are depicted. For example, panel a and b show a lot of orange dots, too.
Also, the the color bar is somewhat ambiguous in assigning colors to waveform classes. (Maybe stretch it from -0.5 to 20.5, then the ticks at 0, 1, ..., 20 are in the centre of their color block)
Response 22: We will revisit this figure in light of the reviewer’s comments to make sure the information is presented clearly and unambiguously,
Comment 23: Congratulations for Figure 15. I like your graphical indication of waveform classes at the top of the figure!
Yet I have some minor comments on this figure.
- Choose one name for class 9: either "very complex echo" (as in Tab. 2, 8, 9) or "unclassified" as in the top of Fig. 15.
- There is maybe too much graphical emphasis on the outliers. - certainly a matter of taste.
- Figure 15 caption, last sentence: I guess the order must be changed into "Classes 8, 12, 14, 19-20 and 10, 13-15, 17-20" to match the order "ERS and Envisat"
Throughout the paper, be consistent in writing Envisat (rather than ENVISAT)
Response 23: As requested, we will replace "unclassified" with “Very complex echo” in Figure 15; we will trial alternative plotting to place less emphasis on outliers; we will change the order in which the classes are listed; and we will also maintain a consistent form for Envisat throughout the manuscript.
Comment 24: line 534ff "In contrast, relatively specular (classes 2 and 4) and multipeaked (class 3) waveforms generally produce a negative elevation bias, although the degradation in performance is less severe for Envisat than the preceding missions."
The second half of this sentence is substantiated for class 3 but not for classes 2 and 4. Maybe limit this consideration to class 3, as occurance of class 2 and 4 is rare.
Response 24: Agreed; we will limit this statement to class 3 only, as suggested.
Comment 25: line 539 "For Envisat, beyond classes 1, 3 and 7, the most common remaining classes are 9 (very complex) and 11 (stepped leading edge)."
This sentence seems to suggest that classes 9 and 11 are less common than classes 1, 3, 7, but this is not the case.
Response 25: We agree that our wording was ambiguous here and so we will modify the text to make this statement clearer.
Comment 26: Fig. 16 caption: in line 571, "(row 1)" does not appear to make sense to me.
Response 26: Agreed, we will remove ‘(row 1)’ as it is redundant given that the panels are labelled.
Citation: https://doi.org/10.5194/egusphere-2024-3446-AC1
-
AC1: 'Reply on RC1', Maya Suryawanshi, 14 Mar 2025
-
RC2: 'Comment on egusphere-2024-3446', Anonymous Referee #2, 13 Feb 2025
This paper presents an important contribution to the field of ice sheet monitoring by improving the accuracy and consistency of satellite radar altimetry data from ERS-1, ERS-2, and Envisat. The research is highly relevant given the significant acceleration in ice loss from the Greenland and Antarctic Ice Sheets over the past three decades.
A key strength of the study is its focus on refining data from older historical satellite missions. By optimizing retrieval methods and evaluating measurement accuracy through comparisons with independent airborne datasets, the authors provide a more reliable multi-decadal record of ice sheet elevation changes. This effort enhances the ability to assess long-term trends in ice sheet imbalance, placing contemporary observations in a broader temporal context.
The study is well-motivated and addresses a critical gap in the accurate long-term monitoring of ice sheets. The findings have wide-ranging applications, including improving estimates of ice mass loss. The comprehensive validation of the new datasets further strengthens the credibility of the results.
However, a more detailed discussion of the specific retrieval methods used and how they compare to prior approaches would enhance the clarity of the study's technical advancements. Additionally, insights into the potential limitations of the new datasets and their implications for future research would provide a more balanced perspective. Including a section on the limitations of the new data product would strengthen the manuscript.
It is important for reviewers to have access to the new dataset during the review process. I find the following statement confusing: “The datasets generated in this study will be made publicly available by the European Space Agency…” When will the data be available? next year? The authors could consider providing a private link for review purposes. At this moment, I am unable to provide feedback on the data (file format, structure, uncertainties, etc.). Since this paper is a data paper, I find it strange that the data is not already available.
EGUsphere is not a data journal (unless I am mistaken), unlike ESSD, for example. To justify publication in EGUsphere, the authors should present novel scientific insights. For instance, they could provide an ice volume estimate using the new and improved data product or compare it with other ice loss studies and highlight the differences. This will also emphasize the importance of the new data.
Airborne campaign data is used to validate the new ERS-1, ERS-2, and Envisat products. Why not use airborne campaign data from 2002 to 2012? Figure 6 shows elevation differences (Envisat minus airborne) during March–May 2009, but does this change over time?
Figure 1: In panel 1b, the areas with no data are difficult to discern.
Citation: https://doi.org/10.5194/egusphere-2024-3446-RC2 -
AC2: 'Reply on RC2', Maya Suryawanshi, 14 Mar 2025
We thank the reviewer for their comments. We address each of the points raised below, with our response provided after each comment.
Initial summary comment: This paper presents an important contribution to the field of ice sheet monitoring by improving the accuracy and consistency of satellite radar altimetry data from ERS-1, ERS-2, and Envisat. The research is highly relevant given the significant acceleration in ice loss from the Greenland and Antarctic Ice Sheets over the past three decades.
A key strength of the study is its focus on refining data from older historical satellite missions. By optimizing retrieval methods and evaluating measurement accuracy through comparisons with independent airborne datasets, the authors provide a more reliable multi-decadal record of ice sheet elevation changes. This effort enhances the ability to assess long-term trends in ice sheet imbalance, placing contemporary observations in a broader temporal context.
The study is well-motivated and addresses a critical gap in the accurate long-term monitoring of ice sheets. The findings have wide-ranging applications, including improving estimates of ice mass loss. The comprehensive validation of the new datasets further strengthens the credibility of the results.
Response: Thank you for these comments, we are glad that the reviewer found this work to be important and to address a critical gap in this area.
Comment 1: However, a more detailed discussion of the specific retrieval methods used and how they compare to prior approaches would enhance the clarity of the study's technical advancements.
Response 1: As requested, we will review our description of the retrieval methods used and where needed we will add further detail relating to the specifics of the method employed and how they compare to prior approaches.
Comment 2: Additionally, insights into the potential limitations of the new datasets and their implications for future research would provide a more balanced perspective. Including a section on the limitations of the new data product would strengthen the manuscript.
Response 2: As requested, we will add a dedicated section on limitations and implications for future research, including recommendations for future research and technical advances needed.
Comment 3: It is important for reviewers to have access to the new dataset during the review process. I find the following statement confusing: “The datasets generated in this study will be made publicly available by the European Space Agency…” When will the data be available? next year? The authors could consider providing a private link for review purposes. At this moment, I am unable to provide feedback on the data (file format, structure, uncertainties, etc.). Since this paper is a data paper, I find it strange that the data is not already available.
Response 3: We apologise for this oversight, and can confirm that the data are now publicly available and distributed by ESA. Further details relating to data access can be found at https://earth.esa.int/eogateway/catalog/tdp-for-land-ice. We will update the manuscript to make this clear.
Comment 4: EGUsphere is not a data journal (unless I am mistaken), unlike ESSD, for example. To justify publication in EGUsphere, the authors should present novel scientific insights. For instance, they could provide an ice volume estimate using the new and improved data product or compare it with other ice loss studies and highlight the differences. This will also emphasize the importance of the new data.
Response 4: Please also see the related response to reviewer 1, who we note was happy that the analysis presented was well aligned with the scope of The Cryosphere. We do acknowledge this request though, and so we shall consider what additional analysis can be included to address this point, noting that the manuscript is already rather long and the analysis quite extensive.
Comment 5: Airborne campaign data is used to validate the new ERS-1, ERS-2, and Envisat products. Why not use airborne campaign data from 2002 to 2012? Figure 6 shows elevation differences (Envisat minus airborne) during March–May 2009, but does this change over time?
Response 5: As noted, we have used airborne campaign data to validate each of the new ERS-1, ERS-2 and Envisat products, and to perform comparison to previous products, namely REAPER and Envisat version 3. In choosing validation cycles, we selected those where there was the greatest coverage of airborne data. Whilst we acknowledge that it would be possible to also use data from other cycles where the airborne coverage was lower, we note that our analysis already goes far beyond the level of validation previously performed (e.g. Brockley et al., 2017) and provides a relatively extensive validation test scenario in its current state, which provides a comprehensive assessment of the quality of the data. Regarding the specific point about attempting to constrain changing elevation differences through time, due to the highly heterogenous sampling provided in different years by the different flight plans, we do not believe it would be feasible to do this with confidence. We will nonetheless make our reasoning for these decisions clearer within the revised manuscript.
Brockley, D. J., Baker, S., Femenias, P., Martinez, B., Massmann, F. H., Otten, M., Paul, F., Picard, B., Prandi, P., Roca, M., Rudenko, S., Scharroo, R., & Visser, P. (2017). REAPER: Reprocessing 12 Years of ERS-1 and ERS-2 Altimeters and Microwave Radiometer Data. IEEE Transactions on Geoscience and Remote Sensing, 55(10), 5506 - 5514. https://doi.org/10.1109/TGRS.2017.2709343
Comment 6: Figure 1: In panel 1b, the areas with no data are difficult to discern.
Response 6: As requested, we will alter the presentation of this figure to better distinguish areas with no data.
Citation: https://doi.org/10.5194/egusphere-2024-3446-AC2
-
AC2: 'Reply on RC2', Maya Suryawanshi, 14 Mar 2025
-
EC1: 'Comment on egusphere-2024-3446', Benjamin Smith, 14 Feb 2025
Dear Dr. Suryawanshi,
Now that we have two referee reports in hand, it seems worthwhile getting started on a response. Both reports are quite positive, and should be fairly straightforward to address, I'm going to close the comment phase, and will look forward to seeing your response to the referees.Best
Ben
Citation: https://doi.org/10.5194/egusphere-2024-3446-EC1 -
AC3: 'Reply on EC1', Maya Suryawanshi, 14 Mar 2025
Dear Ben,
Thank you for your response. We have now posted our response to both of the reviewers’ comments. We look forward to hearing back from you soon.
Best wishes,
Maya
Citation: https://doi.org/10.5194/egusphere-2024-3446-AC3
-
AC3: 'Reply on EC1', Maya Suryawanshi, 14 Mar 2025
-
EC2: 'Comment on egusphere-2024-3446', Benjamin Smith, 14 Feb 2025
Dear Dr. Suryawanshi,
Now that we have two referee reports in hand, it seems worthwhile getting started on a response. Both reports are quite positive, and should be fairly straightforward to address, I'm going to close the comment phase, and will look forward to seeing your response to the referees.Best
Ben
Citation: https://doi.org/10.5194/egusphere-2024-3446-EC2 -
AC4: 'Reply on EC2', Maya Suryawanshi, 14 Mar 2025
Dear Ben,
Thank you for your response. We have now posted our response to both of the reviewers’ comments. We look forward to hearing back from you soon.
Best wishes,
Maya
Citation: https://doi.org/10.5194/egusphere-2024-3446-AC4
-
AC4: 'Reply on EC2', Maya Suryawanshi, 14 Mar 2025
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-3446', Anonymous Referee #1, 17 Jan 2025
The manuscript reports the generation and assessment of new data products of Greenland Ice Sheet and Antarctic Ice Sheet surface elevation from the ERS-1, ERS-2 and Envisat radar altimetry missions. The underlying reprocessing has been performed within ESA's Fundamental Data Records for Altimetry (FDR4ALT) project. It is to supersede the previous REprocessing Altimeter Products for ERS-2 and ERS-2 (REAPER) and the version 3 products for Envisat.
The data products are on the Level-2 level and contain position and surface elevation along track of satellite measurements. In addition a Thematic Data Product (TDP) is provided (which could be classified as Level-2b). It refers all measurements to reference ground tracks and thereby corrects for the non-exact-repeat nature of the orbits and measurements and for the associated topography-induced variations. I expect that this will largely facilitate higher-level analyses for temporal surface elevation change.The improvements in the processing methodology include up-to-data retracking methods and the Roemer et al. 2007 approach of accounting for local topography by relocation.
The new data products, as well as the previous REAPER and Envisat version 3 products are extensively assessed and validated. Comparison to independent surface elevation data from Operatoin ICEBridge is done for Greenland. For both ice sheets, and for the three missions, waveforms are classified (using 21 different classes) through a Neural Network classification. The geographic distribution and histograms of the waveform classes are shown. For Greenland, this allows to assess surface elevation accuracy per waveform class, with very interesting insights and hints to future work on the waveform classes associated with low accuracy. It is shown convincingly that the new products outperform the previous products in virtually all aspects considered.
I enjoyed reading this manuscript. It is extremely clear and informative, starting with the helpful and succinct summary of the three missions in Section 2.1.-2.3 through the illustration on how the TMP simplifies variability in Section 3.4. Thank you for making the review work so easy.
I only have a few minor-to-moderate comments on how the presentation could be further improved.
From the abstract and even from the introduction it is not clear what kind of dataset is presented. For example, readers of a certain background might expect a gridded data product. So you might specify that it is a Level-2 dataset comprising horizontal coordinates (lat lon, or some projection?) and surface elevation (ellipsoidal heights?) sampled along the satellite track.
The manuscript presents datasets (rather than cryospheric science results). Therefore it would be really appropriate to provide public access to the datasets at the time of publishing the paper, at latest. Currently, the manuscript does not comply with TC data policy (https://www.the-cryosphere.net/policies/data_policy.html)
One might even argue that a data journal like ESSD might be more appropriate for this work. Anyway, I would not mind to see this work published in "The Cryosphere" because the excellent analysis of the data (such as the dependence of accuracy on slope and waveform classes) really facilitates understanding the nature of altimetric surface elevation measurements. And this is the basis for a lot of science.
On a similar line, the reader is referred to technical documents for details of the processing (The FDR4ALT Detailed Processing Model Document; the FDR4ALT Product User Guide), which are currently available at websites. It would be desirable to see some commitment for their persistent availability. (It's also curious that these documents have "confidential" at the bottom of every page.)
I'm not going to insist on this comment, though, as I understand it may not be trivial.The abstract could be a bit more specific as to what kind of improvements have been implemented in the processing and what improvements could be achieved w.r.t. previous datasets.
Concerning the validation by ICEBridge data, the reader might wonder why this exercise was restricted to Greenland. Maybe you can explain or justify this limitation in a sentence or two.
line 84 "had the impact of" --> "had the effect of"
line 704 something wrong about this reference "Team, I"
line 702 same problemIn the disucssion of the relocation you might mention that the geographic position assigned to the measurement is corrected together with the height. This is (of course) not reflected in Eq. 1.
line 187: As fas as I understand, the ocean tide and inverse barometer effect are zero over ice sheets. This could be mentioned for completeness.
289 "mean square error". Maybe "mean square difference" might be a more appropriate term.
line 292ff: The reader learns that this classification was performed for waveforms from not only over the ice sheet.
Make sure in the text that the reader understands which steps are done for global altimetry data and which steps are done specifically for ice sheets.line 345 "less continuous along-track sampling"
I think you could sell this point more positively and avoid the impression (at first reading of this sentence) that this is some disadvantage.line 374 replace "Threshold Centre of Gravity" by TCOG for consistency and brevity.
Fig. 6: This is a great visualisation. Just the histogram insets are too small to be well readable, at least in a printed version. You may try to make them a bit bigger. And convince the journal in the layout process to use the full paper width for the figure. In turn you might cut the headline "Envisat | cycle 78" and put this information into the figure description.
Somehow, Figure 10 is missing completely.
Fig. 12a: It appears that slopes are shown not only for the ice sheet area, which is inconsistent with what is sayed in the figure caption and with the other figures in the manuscript.
line 490f "Comparing performance across the three missions shows an apparent lower accuracy of Envisat at higher slopes, which is likely to
reflect the increased coverage that Envisat achieves in these regions (Figure 5)."
I suggest to replace "Comparing performance" by "Comparing the performance of FDR4ALT" in order to be cristal-clear.
I suggest the reference to Fig. 5 should be replaced by a reference to Table 7, because the increased coverage cannot easily seen from Fig. 5, while it is clearly quantified in Table 7Fig. 12 caption: I suggest to shorten the description by writing something like:
"d and e: same as b and c, but for ERS-2. f and g: same as b and c, but for Envisat"Fig 13 and 14. The caption says "The spatial distribution of the five most common waveform classes". However it seems that not only the five most common classes are depicted. For example, panel a and b show a lot of orange dots, too.
Also, the the color bar is somewhat ambiguous in assigning colors to waveform classes. (Maybe stretch it from -0.5 to 20.5, then the ticks at 0, 1, ..., 20 are in the centre of their color block)
Congratulations for Figure 15. I like your graphical indication of waveform classes at the top of the figure!
Yet I have some minor comments on this figure.
- Choose one name for class 9: either "very complex echo" (as in Tab. 2, 8, 9) or "unclassified" as in the top of Fig. 15.
- There is maybe too much graphical emphasis on the outliers. - certainly a matter of taste.
- Figure 15 caption, last sentence: I guess the order must be changed into "Classes 8, 12, 14, 19-20 and 10, 13-15, 17-20" to match the order "ERS and Envisat"Throughout the paper, be consistent in writing Envisat (rather than ENVISAT)
line 534ff "In contrast, relatively specular (classes 2 and 4) and multipeaked (class 3) waveforms generally produce a negative elevation bias, although the degradation in performance is less severe for Envisat than the preceding missions."
The second half of this sentence is substantiated for class 3 but not for classes 2 and 4. Maybe limit this consideration to class 3, as occurance of class 2 and 4 is rare.line 539 "For Envisat, beyond classes 1, 3 and 7, the most common remaining classes are 9 (very complex) and 11 (stepped leading edge)."
This sentence seems to suggest that classes 9 and 11 are less common than classes 1, 3, 7, but this is not the case.Fig. 16 caption: in line 571, "(row 1)" does not appear to make sense to me.
Citation: https://doi.org/10.5194/egusphere-2024-3446-RC1 -
AC1: 'Reply on RC1', Maya Suryawanshi, 14 Mar 2025
We thank the reviewer for their comments. We address each of the points raised below, with our response provided after each comment.
Initial summary comment: The manuscript reports the generation and assessment of new data products of Greenland Ice Sheet and Antarctic Ice Sheet surface elevation from the ERS-1, ERS-2 and Envisat radar altimetry missions. The underlying reprocessing has been performed within ESA's Fundamental Data Records for Altimetry (FDR4ALT) project. It is to supersede the previous REprocessing Altimeter Products for ERS-2 and ERS-2 (REAPER) and the version 3 products for Envisat.
The data products are on the Level-2 level and contain position and surface elevation along track of satellite measurements. In addition a Thematic Data Product (TDP) is provided (which could be classified as Level-2b). It refers all measurements to reference ground tracks and thereby corrects for the non-exact-repeat nature of the orbits and measurements and for the associated topography-induced variations. I expect that this will largely facilitate higher-level analyses for temporal surface elevation change.
The improvements in the processing methodology include up-to-data retracking methods and the Roemer et al. 2007 approach of accounting for local topography by relocation.
The new data products, as well as the previous REAPER and Envisat version 3 products are extensively assessed and validated. Comparison to independent surface elevation data from Operatoin ICEBridge is done for Greenland. For both ice sheets, and for the three missions, waveforms are classified (using 21 different classes) through a Neural Network classification. The geographic distribution and histograms of the waveform classes are shown. For Greenland, this allows to assess surface elevation accuracy per waveform class, with very interesting insights and hints to future work on the waveform classes associated with low accuracy. It is shown convincingly that the new products outperform the previous products in virtually all aspects considered.
I enjoyed reading this manuscript. It is extremely clear and informative, starting with the helpful and succinct summary of the three missions in Section 2.1.-2.3 through the illustration on how the TMP simplifies variability in Section 3.4. Thank you for making the review work so easy.
Response: Thank you for these comments, we appreciate your recognition of the care we put into preparing the manuscript.
I only have a few minor-to-moderate comments on how the presentation could be further improved.
Comment 1: From the abstract and even from the introduction it is not clear what kind of dataset is presented. For example, readers of a certain background might expect a gridded data product. So you might specify that it is a Level-2 dataset comprising horizontal coordinates (lat lon, or some projection?) and surface elevation (ellipsoidal heights?) sampled along the satellite track.
Response 1: We acknowledge that this was not sufficiently clear, and we will add these details as requested.
Comment 2: The manuscript presents datasets (rather than cryospheric science results). Therefore, it would be really appropriate to provide public access to the datasets at the time of publishing the paper, at latest. Currently, the manuscript does not comply with TC data policy (https://www.the-cryosphere.net/policies/data_policy.html). One might even argue that a data journal like ESSD might be more appropriate for this work. Anyway, I would not mind to see this work published in "The Cryosphere" because the excellent analysis of the data (such as the dependence of accuracy on slope and waveform classes) really facilitates understanding the nature of altimetric surface elevation measurements. And this is the basis for a lot of science.
Response 2: We agree, and can confirm that the data are now publicly available and distributed by ESA. Further details on how to access the data can be found at https://earth.esa.int/eogateway/catalog/tdp-for-land-ice. We will update the manuscript to make this clear. Regarding our wish to publish this work in The Cryosphere rather than ESSD, we agree that in principle it would be in scope for both journals. At the stage of initial submission, we discussed this amongst all coauthors, and decided that we preferred to submit to the former. At this stage, we would like to continue along this route, and so we are happy that the reviewer appreciates the appropriateness of this approach.
Comment 3: On a similar line, the reader is referred to technical documents for details of the processing (The FDR4ALT Detailed Processing Model Document; the FDR4ALT Product User Guide), which are currently available at websites. It would be desirable to see some commitment for their persistent availability. (It's also curious that these documents have "confidential" at the bottom of every page.) I'm not going to insist on this comment, though, as I understand it may not be trivial.
Response 3: These documents are currently hosted by ESA, due to their funding of the work. As part of our revisions, we will explore with them what commitment they can provide in terms of persistence.
Comment 4: The abstract could be a bit more specific as to what kind of improvements have been implemented in the processing and what improvements could be achieved w.r.t. previous datasets.
Response 4: As requested, we will revise the abstract to include these specifics.
Comment 5: Concerning the validation by ICEBridge data, the reader might wonder why this exercise was restricted to Greenland. Maybe you can explain or justify this limitation in a sentence or two.
Response 5: As requested, we will add additional details to explain the justification for this approach. We selected Greenland for validation purposes because (1) it provided the most extensive coverage of validation data for all missions, most notably for pre-IceBridge campaigns where coverage over Antarctica is extremely limited, and (2) it encompassed a broad range of topographic complexity and surface characteristics. We believe that in doing so, our analysis provides a relatively comprehensive assessment of data accuracy, and advances beyond previous work.
Comment 6: line 84 "had the impact of" --> "had the effect of"
Response 6: Agreed; we will update the manuscript as suggested.
Comment 7: line 704 something wrong about this reference "Team, I"
Response 7: Agreed; we will correct this.
Comment 8: line 702 same problem
Response 8: Agreed; we will correct this.
Comment 9: In the discussion of the relocation you might mention that the geographic position assigned to the measurement is corrected together with the height. This is (of course) not reflected in Eq. 1.
Response 9: We will mention this as requested.
Comment 10: line 187: As fas as I understand, the ocean tide and inverse barometer effect are zero over ice sheets. This could be mentioned for completeness.
Response 10: Yes this is correct; we will add text to mention this as requested.
Comment 11: 289 "mean square error". Maybe "mean square difference" might be a more appropriate term.
Response 11: Agreed; we will change this as suggested.
.
Comment 12: line 292ff: The reader learns that this classification was performed for waveforms from not only over the ice sheet.
Response 12: Yes this is correct.
Comment 13: Make sure in the text that the reader understands which steps are done for global altimetry data and which steps are done specifically for ice sheets.
Response 13: As requested, we will make sure it is clear which steps have been performed for global altimetry data.
Comment 14: line 345 "less continuous along-track sampling". I think you could sell this point more positively and avoid the impression (at first reading of this sentence) that this is some disadvantage.
Response 14: As suggested, we will reword this more positively.
Comment 15: line 374 replace "Threshold Centre of Gravity" by TCOG for consistency and brevity.
Response 15: Agreed; we will change this as suggested.
Comment 16: Fig. 6: This is a great visualisation. Just the histogram insets are too small to be well readable, at least in a printed version. You may try to make them a bit bigger. And convince the journal in the layout process to use the full paper width for the figure. In turn you might cut the headline "Envisat | cycle 78" and put this information into the figure description.
Response 16: We will look to modify the layout of this figure to address the point raised.
Comment 17: Somehow, Figure 10 is missing completely.
Response 17: We apologise for this omission and we will add the figure in the revised version.
Comment 18: Fig. 12a: It appears that slopes are shown not only for the ice sheet area, which is inconsistent with what is sayed in the figure caption and with the other figures in the manuscript.
Response 18: We will update the figure to ensure that it only shows surface slope for the ice sheet itself.
Comment 19: line 490f "Comparing performance across the three missions shows an apparent lower accuracy of Envisat at higher slopes, which is likely to reflect the increased coverage that Envisat achieves in these regions (Figure 5)." I suggest to replace "Comparing performance" by "Comparing the performance of FDR4ALT" in order to be cristal-clear.
Response 19: Agreed; we will update the manuscript to reflect this suggestion.
Comment 20: I suggest the reference to Fig. 5 should be replaced by a reference to Table 7, because the increased coverage cannot easily seen from Fig. 5, while it is clearly quantified in Table 7
Response 20: Agreed; we will replace the reference to Fig. 5 with a reference to Table 7.
Comment 21: Fig. 12 caption: I suggest to shorten the description by writing something like:
"d and e: same as b and c, but for ERS-2. f and g: same as b and c, but for Envisat"
Response 21: We will shorten the caption, as suggested.
Comment 22: Fig 13 and 14. The caption says "The spatial distribution of the five most common waveform classes". However it seems that not only the five most common classes are depicted. For example, panel a and b show a lot of orange dots, too.
Also, the the color bar is somewhat ambiguous in assigning colors to waveform classes. (Maybe stretch it from -0.5 to 20.5, then the ticks at 0, 1, ..., 20 are in the centre of their color block)
Response 22: We will revisit this figure in light of the reviewer’s comments to make sure the information is presented clearly and unambiguously,
Comment 23: Congratulations for Figure 15. I like your graphical indication of waveform classes at the top of the figure!
Yet I have some minor comments on this figure.
- Choose one name for class 9: either "very complex echo" (as in Tab. 2, 8, 9) or "unclassified" as in the top of Fig. 15.
- There is maybe too much graphical emphasis on the outliers. - certainly a matter of taste.
- Figure 15 caption, last sentence: I guess the order must be changed into "Classes 8, 12, 14, 19-20 and 10, 13-15, 17-20" to match the order "ERS and Envisat"
Throughout the paper, be consistent in writing Envisat (rather than ENVISAT)
Response 23: As requested, we will replace "unclassified" with “Very complex echo” in Figure 15; we will trial alternative plotting to place less emphasis on outliers; we will change the order in which the classes are listed; and we will also maintain a consistent form for Envisat throughout the manuscript.
Comment 24: line 534ff "In contrast, relatively specular (classes 2 and 4) and multipeaked (class 3) waveforms generally produce a negative elevation bias, although the degradation in performance is less severe for Envisat than the preceding missions."
The second half of this sentence is substantiated for class 3 but not for classes 2 and 4. Maybe limit this consideration to class 3, as occurance of class 2 and 4 is rare.
Response 24: Agreed; we will limit this statement to class 3 only, as suggested.
Comment 25: line 539 "For Envisat, beyond classes 1, 3 and 7, the most common remaining classes are 9 (very complex) and 11 (stepped leading edge)."
This sentence seems to suggest that classes 9 and 11 are less common than classes 1, 3, 7, but this is not the case.
Response 25: We agree that our wording was ambiguous here and so we will modify the text to make this statement clearer.
Comment 26: Fig. 16 caption: in line 571, "(row 1)" does not appear to make sense to me.
Response 26: Agreed, we will remove ‘(row 1)’ as it is redundant given that the panels are labelled.
Citation: https://doi.org/10.5194/egusphere-2024-3446-AC1
-
AC1: 'Reply on RC1', Maya Suryawanshi, 14 Mar 2025
-
RC2: 'Comment on egusphere-2024-3446', Anonymous Referee #2, 13 Feb 2025
This paper presents an important contribution to the field of ice sheet monitoring by improving the accuracy and consistency of satellite radar altimetry data from ERS-1, ERS-2, and Envisat. The research is highly relevant given the significant acceleration in ice loss from the Greenland and Antarctic Ice Sheets over the past three decades.
A key strength of the study is its focus on refining data from older historical satellite missions. By optimizing retrieval methods and evaluating measurement accuracy through comparisons with independent airborne datasets, the authors provide a more reliable multi-decadal record of ice sheet elevation changes. This effort enhances the ability to assess long-term trends in ice sheet imbalance, placing contemporary observations in a broader temporal context.
The study is well-motivated and addresses a critical gap in the accurate long-term monitoring of ice sheets. The findings have wide-ranging applications, including improving estimates of ice mass loss. The comprehensive validation of the new datasets further strengthens the credibility of the results.
However, a more detailed discussion of the specific retrieval methods used and how they compare to prior approaches would enhance the clarity of the study's technical advancements. Additionally, insights into the potential limitations of the new datasets and their implications for future research would provide a more balanced perspective. Including a section on the limitations of the new data product would strengthen the manuscript.
It is important for reviewers to have access to the new dataset during the review process. I find the following statement confusing: “The datasets generated in this study will be made publicly available by the European Space Agency…” When will the data be available? next year? The authors could consider providing a private link for review purposes. At this moment, I am unable to provide feedback on the data (file format, structure, uncertainties, etc.). Since this paper is a data paper, I find it strange that the data is not already available.
EGUsphere is not a data journal (unless I am mistaken), unlike ESSD, for example. To justify publication in EGUsphere, the authors should present novel scientific insights. For instance, they could provide an ice volume estimate using the new and improved data product or compare it with other ice loss studies and highlight the differences. This will also emphasize the importance of the new data.
Airborne campaign data is used to validate the new ERS-1, ERS-2, and Envisat products. Why not use airborne campaign data from 2002 to 2012? Figure 6 shows elevation differences (Envisat minus airborne) during March–May 2009, but does this change over time?
Figure 1: In panel 1b, the areas with no data are difficult to discern.
Citation: https://doi.org/10.5194/egusphere-2024-3446-RC2 -
AC2: 'Reply on RC2', Maya Suryawanshi, 14 Mar 2025
We thank the reviewer for their comments. We address each of the points raised below, with our response provided after each comment.
Initial summary comment: This paper presents an important contribution to the field of ice sheet monitoring by improving the accuracy and consistency of satellite radar altimetry data from ERS-1, ERS-2, and Envisat. The research is highly relevant given the significant acceleration in ice loss from the Greenland and Antarctic Ice Sheets over the past three decades.
A key strength of the study is its focus on refining data from older historical satellite missions. By optimizing retrieval methods and evaluating measurement accuracy through comparisons with independent airborne datasets, the authors provide a more reliable multi-decadal record of ice sheet elevation changes. This effort enhances the ability to assess long-term trends in ice sheet imbalance, placing contemporary observations in a broader temporal context.
The study is well-motivated and addresses a critical gap in the accurate long-term monitoring of ice sheets. The findings have wide-ranging applications, including improving estimates of ice mass loss. The comprehensive validation of the new datasets further strengthens the credibility of the results.
Response: Thank you for these comments, we are glad that the reviewer found this work to be important and to address a critical gap in this area.
Comment 1: However, a more detailed discussion of the specific retrieval methods used and how they compare to prior approaches would enhance the clarity of the study's technical advancements.
Response 1: As requested, we will review our description of the retrieval methods used and where needed we will add further detail relating to the specifics of the method employed and how they compare to prior approaches.
Comment 2: Additionally, insights into the potential limitations of the new datasets and their implications for future research would provide a more balanced perspective. Including a section on the limitations of the new data product would strengthen the manuscript.
Response 2: As requested, we will add a dedicated section on limitations and implications for future research, including recommendations for future research and technical advances needed.
Comment 3: It is important for reviewers to have access to the new dataset during the review process. I find the following statement confusing: “The datasets generated in this study will be made publicly available by the European Space Agency…” When will the data be available? next year? The authors could consider providing a private link for review purposes. At this moment, I am unable to provide feedback on the data (file format, structure, uncertainties, etc.). Since this paper is a data paper, I find it strange that the data is not already available.
Response 3: We apologise for this oversight, and can confirm that the data are now publicly available and distributed by ESA. Further details relating to data access can be found at https://earth.esa.int/eogateway/catalog/tdp-for-land-ice. We will update the manuscript to make this clear.
Comment 4: EGUsphere is not a data journal (unless I am mistaken), unlike ESSD, for example. To justify publication in EGUsphere, the authors should present novel scientific insights. For instance, they could provide an ice volume estimate using the new and improved data product or compare it with other ice loss studies and highlight the differences. This will also emphasize the importance of the new data.
Response 4: Please also see the related response to reviewer 1, who we note was happy that the analysis presented was well aligned with the scope of The Cryosphere. We do acknowledge this request though, and so we shall consider what additional analysis can be included to address this point, noting that the manuscript is already rather long and the analysis quite extensive.
Comment 5: Airborne campaign data is used to validate the new ERS-1, ERS-2, and Envisat products. Why not use airborne campaign data from 2002 to 2012? Figure 6 shows elevation differences (Envisat minus airborne) during March–May 2009, but does this change over time?
Response 5: As noted, we have used airborne campaign data to validate each of the new ERS-1, ERS-2 and Envisat products, and to perform comparison to previous products, namely REAPER and Envisat version 3. In choosing validation cycles, we selected those where there was the greatest coverage of airborne data. Whilst we acknowledge that it would be possible to also use data from other cycles where the airborne coverage was lower, we note that our analysis already goes far beyond the level of validation previously performed (e.g. Brockley et al., 2017) and provides a relatively extensive validation test scenario in its current state, which provides a comprehensive assessment of the quality of the data. Regarding the specific point about attempting to constrain changing elevation differences through time, due to the highly heterogenous sampling provided in different years by the different flight plans, we do not believe it would be feasible to do this with confidence. We will nonetheless make our reasoning for these decisions clearer within the revised manuscript.
Brockley, D. J., Baker, S., Femenias, P., Martinez, B., Massmann, F. H., Otten, M., Paul, F., Picard, B., Prandi, P., Roca, M., Rudenko, S., Scharroo, R., & Visser, P. (2017). REAPER: Reprocessing 12 Years of ERS-1 and ERS-2 Altimeters and Microwave Radiometer Data. IEEE Transactions on Geoscience and Remote Sensing, 55(10), 5506 - 5514. https://doi.org/10.1109/TGRS.2017.2709343
Comment 6: Figure 1: In panel 1b, the areas with no data are difficult to discern.
Response 6: As requested, we will alter the presentation of this figure to better distinguish areas with no data.
Citation: https://doi.org/10.5194/egusphere-2024-3446-AC2
-
AC2: 'Reply on RC2', Maya Suryawanshi, 14 Mar 2025
-
EC1: 'Comment on egusphere-2024-3446', Benjamin Smith, 14 Feb 2025
Dear Dr. Suryawanshi,
Now that we have two referee reports in hand, it seems worthwhile getting started on a response. Both reports are quite positive, and should be fairly straightforward to address, I'm going to close the comment phase, and will look forward to seeing your response to the referees.Best
Ben
Citation: https://doi.org/10.5194/egusphere-2024-3446-EC1 -
AC3: 'Reply on EC1', Maya Suryawanshi, 14 Mar 2025
Dear Ben,
Thank you for your response. We have now posted our response to both of the reviewers’ comments. We look forward to hearing back from you soon.
Best wishes,
Maya
Citation: https://doi.org/10.5194/egusphere-2024-3446-AC3
-
AC3: 'Reply on EC1', Maya Suryawanshi, 14 Mar 2025
-
EC2: 'Comment on egusphere-2024-3446', Benjamin Smith, 14 Feb 2025
Dear Dr. Suryawanshi,
Now that we have two referee reports in hand, it seems worthwhile getting started on a response. Both reports are quite positive, and should be fairly straightforward to address, I'm going to close the comment phase, and will look forward to seeing your response to the referees.Best
Ben
Citation: https://doi.org/10.5194/egusphere-2024-3446-EC2 -
AC4: 'Reply on EC2', Maya Suryawanshi, 14 Mar 2025
Dear Ben,
Thank you for your response. We have now posted our response to both of the reviewers’ comments. We look forward to hearing back from you soon.
Best wishes,
Maya
Citation: https://doi.org/10.5194/egusphere-2024-3446-AC4
-
AC4: 'Reply on EC2', Maya Suryawanshi, 14 Mar 2025
Peer review completion
Journal article(s) based on this preprint
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 365 | 124 | 28 | 517 | 15 | 25 |
- HTML: 365
- PDF: 124
- XML: 28
- Total: 517
- BibTeX: 15
- EndNote: 25
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
Maya Raghunath Suryawanshi
Malcolm McMillan
Jennifer Maddalena
Fanny Piras
Jérémie Aublanc
Jean-Alexis Daguzé
Clara Grau
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(13909 KB) - Metadata XML