the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 Nov 2023
Single-blind detection, localization, and quantification of methane emissions using continuous path-integrated column measurements
Abstract. Path-integrated column measurements with a laser absorption-based measurement system have been used to detect, locate, and quantify methane (CH4) emissions from a series of single-blind controlled releases with no prior knowledge of timing, locations, or release rates. System performance was evaluated against metrics defined in the Continuous Monitoring Protocol established by the Methane Emissions Technology Evaluation Center (METEC) at Colorado State University. This protocol allows more direct comparison of system performance between disparate measurement technologies. This experiment differs from similar tests where releases were conducted from equipment units at fixed locations at METEC by instead conducting releases at random locations anywhere within the central 0.18 km2 of a 0.35 km2 test site. The releases were much shorter in duration than those conducted in similar testing at METEC. The system detected 25 of 42 releases, which ranged in metered rate from 0.17 to 2.15 kg/h. The minimum detected emissions rate was 0.22 kg/h, and the system demonstrated a 100 % detection rate for releases ≥0.65 kg/h and average wind speed <5 m/s. The test site was subdivided into 20 boxes (109 × 83 m each), and the correct release box was identified in 9 cases, another 9 detections were localized to an adjacent box, and the remaining 7 were attributed elsewhere within the field. The average estimated emission rate bias was -6.1 %. The 90 % detection limit was 0.89 kg/h, while the wind-normalized detection limit was 0.44 (kg/h)/(m/s).
Status: closed
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RC1: 'Comment on egusphere-2023-2602', Anonymous Referee #1, 04 Jan 2024
General comments
The paper presents another important test for application of a laser absorption based ground-based measurement system for monitoring methane emissions over complex areas (facilities or cities) as part of a series of recent publications on the subject. The paper is mostly well written and provides the most important references for understanding. Some figures and its captions have to be improved to be suitable for publication.
Specific comments
The paper contains too many abbreviations. If used only one or two times after its definition for the reader it would be better to spell it out every time.
Figure 4, 5: Please define symbols (filled circles) in captions. Do they represent a specific number of observations? Shouldn't their value be only 0 or 1? Please clarify.
Line 290: This remark should reference Fig.3 or occur earlier.
Table 2/line 320: A remark on the meaning of the negative 'CMP' value for 'Facility' would be useful.
Figure 7: Are the individual points per box? For the green points there is almost no linear correlation. Please expand text.
Section 4: Is it possible to include a remark on the share of the puff model and the retrieval method in the uncertainties?
Table C2: It might be useful to include a column with the average wind speed.
Figure D1: What is the meaning of the shading?
Figure D2: For symbols refer to Fig. 1.
Technical corrections
Appendix D and section 2.7: Don't mess up concentration and volume mixing ratio or emission and elevated volume mixing ratio, at least not when the unit is 'ppm'.Citation: https://doi.org/10.5194/egusphere-2023-2602-RC1 -
AC1: 'Reply on RC1', Nathan Blume, 17 Jan 2024
Thank you for the constructive review comments. We have addressed or attempted to address each of them in our revised manuscript, which will be uploaded once all reviewer feedback has been received and addressed. I have included specific responses to each of your comments in the attached file.
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AC1: 'Reply on RC1', Nathan Blume, 17 Jan 2024
-
RC2: 'Comment on egusphere-2023-2602', Anonymous Referee #2, 26 Jan 2024
- Generally, this manuscript’s title, abstract and introduction are a bit misleading. There are multiple references to the METEC test facility, despite these tests not being performed at the METEC or even at a similar facility. These blind tests were performed in an open field without flow obstructions or realistic emitting equipment.
- These tests do not appear to significantly differ from other similar papers describing the dual laser-head tomographic approach.
- There is no oil and gas equipment present and so references to other METEC studies or the implications of these results for the oil and gas field in general should probably be kept to the conclusions or future work sections. For example, It is not reasonable to make assertions of “localization” to equipment units or groups when there was no equipment present.
- The concept of “blind” testing of rates (quantification) should be removed from title, given the rates were not technically blinded (see below).
- The concept of “continuous” should likely also be reconsidered in the title given that “frost heaving” required the system only be run for certain portions of the day. It was not clear what day-to-day manual corrections were made to correct for frost heaving? These should be described more fully.
- The introduction and abstract of this paper do not adequately convey that two different laser heads were used in a tomographic approach. This is an important aspect of the system. This makes the detailed comparisons to different open-path continuous monitoring systems irrelevant – they are fundamentally different approaches. Generally, it should be compared with the broad range of other continuous monitors (e.g., Bell et al. 2023).
- This paper seeks to draw distinctions between the tests performed in a field without realistic oil and gas equipment, with other tests performed at METEC. It is fine to reference and use the METEC protocols, but the detailed comparisons with METEC-published results in the introduction are misleading, given that these tests are fundamentally different on so many levels.
- Some critical differences between the tests performed here and tests performed at METEC:
- In this test, no real oil and gas equipment was used, confounding source characteristics as well as turbulent mixing.
- In this test, high-purity gas was used, not a realistic gas mixture.
- In this test, guidance was provided to testers beforehand about what rates the releases should happen at; this does not occur at METEC.
- This test described “Equipment Group and Unit” localization, but without real equipment in the field, this is impossible to ascertain. The size of the “boxes” were not provided. More importantly, the lack of realistic atmospheric turbulence generated by real equipment was not testable.
- The detailed descriptions of other test protocols on pages 1 and 3 should be removed in favor of a simple reference to the Bell et al. 2023 test protocols. Those test protocols are the only element of METEC that are relevant for this study, since it was not performed at METEC or a similar site. Specifically, the Alden et al. 2019 study uses a different (not tomographic) approach.
- The METEC protocols cited require time-to-detect metrics. These should be discussed in the paper. Similarly, the real-time automated reporting of detected events should be shown.
- Page 5: What are the heights of the reflectors?
- What are the heights of the controlled releases?
- In what ways were the controlled releases structured to mimic oil and gas equipment emissions?
- What are the heights of the two greenlite instruments?
- What calibration of these instruments is required prior to and during deployment?
- What types of calibrations are needed (e.g., water vapor?)
- Page 7: the evaluation of the instrument as installed at the test site to the provide guidance on release rates to the testers invalidates the blind nature of this test, as described above.
- More information is needed on the flat-fielding correction. Was the flat-fielding correction conducted during a period of no releases? How often was this performed and under what circumstances?
- Page 9: it appears this method precludes the possibility of more than one emission source on a monitored site. This should be discussed more fully in the assumptions noted in the blind testing sections above.
- Page 11: the presence of a high number of false positives for on-site and off-site sources should probably be shown in the abstract alongside the true positive results.
- Page 13-15: the direct use of METEC terminology for equipment group and equipment unit is not merited here and is misleading. Without denoting the sizes of each of the “boxes” used, it is not justifiable to imply that equipment-unit localization was tested and proven. Furthermore, localization depends strongly on the turbulent interference imposed by physical oil and gas equipment being located on site. Therefore, it is not justifiable to make such a leap to oil and gas infrastructure.
- Pages 14 and 17: it was not made clear throughout the paper that area sources were being tested, and not point sources. This represents a broadly misleading feature of the article, which supposes to test point sources of oil and gas equipment. The diffuse vs. point source distinction needs to be made much more clear in the introduction, methods, and results sections. The results are very different between point and area sources (fig 7) and so this needs to be a main point of the paper’s methods, results, and conclusions sections.
- Page 21: off-site interference is a real issue in oil and gas monitoring. These events need to be classified as false positives regardless of origin.
Citation: https://doi.org/10.5194/egusphere-2023-2602-RC2 - AC2: 'Reply on RC2', Nathan Blume, 13 Feb 2024
Status: closed
-
RC1: 'Comment on egusphere-2023-2602', Anonymous Referee #1, 04 Jan 2024
General comments
The paper presents another important test for application of a laser absorption based ground-based measurement system for monitoring methane emissions over complex areas (facilities or cities) as part of a series of recent publications on the subject. The paper is mostly well written and provides the most important references for understanding. Some figures and its captions have to be improved to be suitable for publication.
Specific comments
The paper contains too many abbreviations. If used only one or two times after its definition for the reader it would be better to spell it out every time.
Figure 4, 5: Please define symbols (filled circles) in captions. Do they represent a specific number of observations? Shouldn't their value be only 0 or 1? Please clarify.
Line 290: This remark should reference Fig.3 or occur earlier.
Table 2/line 320: A remark on the meaning of the negative 'CMP' value for 'Facility' would be useful.
Figure 7: Are the individual points per box? For the green points there is almost no linear correlation. Please expand text.
Section 4: Is it possible to include a remark on the share of the puff model and the retrieval method in the uncertainties?
Table C2: It might be useful to include a column with the average wind speed.
Figure D1: What is the meaning of the shading?
Figure D2: For symbols refer to Fig. 1.
Technical corrections
Appendix D and section 2.7: Don't mess up concentration and volume mixing ratio or emission and elevated volume mixing ratio, at least not when the unit is 'ppm'.Citation: https://doi.org/10.5194/egusphere-2023-2602-RC1 -
AC1: 'Reply on RC1', Nathan Blume, 17 Jan 2024
Thank you for the constructive review comments. We have addressed or attempted to address each of them in our revised manuscript, which will be uploaded once all reviewer feedback has been received and addressed. I have included specific responses to each of your comments in the attached file.
-
AC1: 'Reply on RC1', Nathan Blume, 17 Jan 2024
-
RC2: 'Comment on egusphere-2023-2602', Anonymous Referee #2, 26 Jan 2024
- Generally, this manuscript’s title, abstract and introduction are a bit misleading. There are multiple references to the METEC test facility, despite these tests not being performed at the METEC or even at a similar facility. These blind tests were performed in an open field without flow obstructions or realistic emitting equipment.
- These tests do not appear to significantly differ from other similar papers describing the dual laser-head tomographic approach.
- There is no oil and gas equipment present and so references to other METEC studies or the implications of these results for the oil and gas field in general should probably be kept to the conclusions or future work sections. For example, It is not reasonable to make assertions of “localization” to equipment units or groups when there was no equipment present.
- The concept of “blind” testing of rates (quantification) should be removed from title, given the rates were not technically blinded (see below).
- The concept of “continuous” should likely also be reconsidered in the title given that “frost heaving” required the system only be run for certain portions of the day. It was not clear what day-to-day manual corrections were made to correct for frost heaving? These should be described more fully.
- The introduction and abstract of this paper do not adequately convey that two different laser heads were used in a tomographic approach. This is an important aspect of the system. This makes the detailed comparisons to different open-path continuous monitoring systems irrelevant – they are fundamentally different approaches. Generally, it should be compared with the broad range of other continuous monitors (e.g., Bell et al. 2023).
- This paper seeks to draw distinctions between the tests performed in a field without realistic oil and gas equipment, with other tests performed at METEC. It is fine to reference and use the METEC protocols, but the detailed comparisons with METEC-published results in the introduction are misleading, given that these tests are fundamentally different on so many levels.
- Some critical differences between the tests performed here and tests performed at METEC:
- In this test, no real oil and gas equipment was used, confounding source characteristics as well as turbulent mixing.
- In this test, high-purity gas was used, not a realistic gas mixture.
- In this test, guidance was provided to testers beforehand about what rates the releases should happen at; this does not occur at METEC.
- This test described “Equipment Group and Unit” localization, but without real equipment in the field, this is impossible to ascertain. The size of the “boxes” were not provided. More importantly, the lack of realistic atmospheric turbulence generated by real equipment was not testable.
- The detailed descriptions of other test protocols on pages 1 and 3 should be removed in favor of a simple reference to the Bell et al. 2023 test protocols. Those test protocols are the only element of METEC that are relevant for this study, since it was not performed at METEC or a similar site. Specifically, the Alden et al. 2019 study uses a different (not tomographic) approach.
- The METEC protocols cited require time-to-detect metrics. These should be discussed in the paper. Similarly, the real-time automated reporting of detected events should be shown.
- Page 5: What are the heights of the reflectors?
- What are the heights of the controlled releases?
- In what ways were the controlled releases structured to mimic oil and gas equipment emissions?
- What are the heights of the two greenlite instruments?
- What calibration of these instruments is required prior to and during deployment?
- What types of calibrations are needed (e.g., water vapor?)
- Page 7: the evaluation of the instrument as installed at the test site to the provide guidance on release rates to the testers invalidates the blind nature of this test, as described above.
- More information is needed on the flat-fielding correction. Was the flat-fielding correction conducted during a period of no releases? How often was this performed and under what circumstances?
- Page 9: it appears this method precludes the possibility of more than one emission source on a monitored site. This should be discussed more fully in the assumptions noted in the blind testing sections above.
- Page 11: the presence of a high number of false positives for on-site and off-site sources should probably be shown in the abstract alongside the true positive results.
- Page 13-15: the direct use of METEC terminology for equipment group and equipment unit is not merited here and is misleading. Without denoting the sizes of each of the “boxes” used, it is not justifiable to imply that equipment-unit localization was tested and proven. Furthermore, localization depends strongly on the turbulent interference imposed by physical oil and gas equipment being located on site. Therefore, it is not justifiable to make such a leap to oil and gas infrastructure.
- Pages 14 and 17: it was not made clear throughout the paper that area sources were being tested, and not point sources. This represents a broadly misleading feature of the article, which supposes to test point sources of oil and gas equipment. The diffuse vs. point source distinction needs to be made much more clear in the introduction, methods, and results sections. The results are very different between point and area sources (fig 7) and so this needs to be a main point of the paper’s methods, results, and conclusions sections.
- Page 21: off-site interference is a real issue in oil and gas monitoring. These events need to be classified as false positives regardless of origin.
Citation: https://doi.org/10.5194/egusphere-2023-2602-RC2 - AC2: 'Reply on RC2', Nathan Blume, 13 Feb 2024
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