the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
ACDL/DQ-1 Calibration Algorithms. Part I: Nighttime 532 nm Polarization and High-Spectral-Resolution Channel
Abstract. The Atmospheric Environment Monitoring Satellite (DQ-1) was successfully launched in April 2022, with the capability of providing continuous multi-sensor spatial and optical simultaneous observations of carbon dioxide, aerosols and clouds. The primary payload carried on DQ-1 is an Aerosol and Carbon dioxide Detection Lidar (ACDL). The instrument comprises a high-spectral-resolution channel at 532 nm, elastic channels at 532 nm and 1064 nm, and integrated-path differential absorption (IPDA) channel at 1572 nm. The optical properties of aerosols and clouds measured by the ACDL promote a quantitative characterization of the uncertainties in the global climate system, hence the precise calibrations for the ACDL are necessary. This paper outlines the algorithms employed for calibrating the nighttime 532 nm measurements for the first spaceborne high-spectral-resolution lidar with an iodine vapor absorption filter. The nighttime calibrations of the 532 nm data are fundamental to the ACDL measurement procedure, as they are utilized to derive the calibrations over daytime orbits and the calibrations of the 1064 nm channel relative to the 532 nm channel. This paper provides a review of the theoretical foundations for molecular normalization techniques as applied to spaceborne lidar measurements, includes a detailed discussion of auxiliary data and theoretical parameters used in ACDL calibrations, as well as a comprehensive description of the calibration algorithm procedure. To mitigate large errors stemming from high-energy events during calibration, a data filter is designed to obtain valid calibration signals. The paper also assesses the results of the calibration procedure, by analysing the errors of calibration coefficients and validating the attenuated backscatter coefficient results. The results indicate that the relative error of the calibrated attenuated backscatter coefficients is lower than 2 % in the calibration area, and the uncertainty of the pure-molecule attenuated scattering ratio was within anticipated range of 5 %.
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RC1: 'Comment on egusphere-2024-588', Anonymous Referee #1, 25 Mar 2024
This manuscript presents the calibration algorithms used for the ACDL lidar onboard the DQ-1 satellite, with the analysis of the 532 nm nighttime polarization and high-spectral-resolution channels. This work is of interest to the lidar community. Also, the upcoming launch of EarthCARE with the ATLID lidar in May 2024 will provide opportunity for further comparative studies between these two advanced lidar systems. I appreciate the efforts made in this study and offer some comments for improvement of this manuscript. Additionally, a careful review of the manuscript for English language improvements is advised, as some sections may benefit from further editing for clarity and grammatical accuracy.
General comments:
- Figure 4: The blue dotted line is indistinguishable from other color curves representing iodine vapor absorption. Please enhance the figure’s visualization quality for better interpretation.
- Figure 7 (a): The large variation in original signals within the SAA region is noticeable, but the overlay of filtered signals obscures the original data in most other regions. Adjusting the transparency level of the filtered data may resolve this issue. This recommendation applies to all subplots in Figure 7.
- Figure 7 (c): There appears to be a discrepancy in the upper left legend; it likely should be labeled as “Parallel Channel” rather than “HSRL channel.”
- The error analysis in this manuscript provides a foundation for assessing calibration accuracy. Can the authors discuss how these error metrics compare with those from other missions or standards in atmospheric lidar measurements, which can offer readers a benchmark for assessing ACDL's performance?
- The manuscript mentions that ACDL data used in the paper are not publicly available. Given the scientific community's growing emphasis on open data for reproducibility and further analysis, consider discussing plans for data availability or establishing a data repository with access protocols, potentially making a portion of the data available.
- The aothors mentioned the plans for further validation tests. Can the authors expand on these plans, perhaps by detailing the types of lidar or other atmospheric sensors against which ACDL's data will be validated?
Technical comments:
- Lines 74-75: Simplify “with selected chose the region…” to “chose the region…” to enhance clarity.
- Lines 80-82: Include the name of the lidar instrument onboard EarthCARE: the ATLID (Atmospheric Lidar).
- Line 139: Suggest rephrasing for clarity: "Defining the normalized signals is a necessary first step for the different channels including:"
- Line 151: Align the order of terms (molecular, ozone, aerosol) with their presentation in Eq(5).
- Line 170: selects 31 -35 km as “the” calibration regions.
- Line 171: Clarification needed – replace “subsection” with “the following paragraphs” if subsections are not explicitly defined.
- Line 182: This sentence is unclear, please rephrase.
- Line 197: If available, include more recent references regarding this lidar ratio selection.
- Line 208: Ensure consistency in the order of terms as previously mentioned.
- Line 285: Correct to “Eq. (26) is” since only one equation is referenced.
- Line 289: Please provide details on defining the empirical scaling factor km, including the specific factor used in this study.
- Figure 7: The subfigure labels (a)(b)(c)(d) are missing or unclear.
- Line 328: Eqs. (32) and (33) are mentioned prematurely; they are introduced in the subsequent section.
- Line 370: A delta symbol is missing before PGR; please verify.
- Line 391: Amend to “can also be assessed” for grammatical accuracy.
Citation: https://doi.org/10.5194/egusphere-2024-588-RC1 -
AC2: 'Reply on RC1', Fanqian Meng, 04 May 2024
Dear Reviewer,
Many thanks for reviewing our manuscript. We greatly appreciate the substantial amount of time and effort that you dedicated to this review process.
We have revised the manuscript according to your comments point-to-point and the response is presented below as the supplement.
Many thanks and best regards.
Fanqian Meng, Junwu Tang and Guangyao Dai
On behalf of the co-authors
Citation: https://doi.org/10.5194/egusphere-2024-588-RC1
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RC2: 'Comment on egusphere-2024-588', Anonymous Referee #2, 07 Apr 2024
-
AC1: 'Reply on RC2', Fanqian Meng, 04 May 2024
Dear Reviewer,
Many thanks for reviewing our manuscript. We greatly appreciate the substantial amount of time and effort that you dedicated to this review process.
We have revised the manuscript according to your comments point-to-point and the response is presented below as the supplement.
Many thanks and best regards.
Fanqian Meng, Junwu Tang and Guangyao Dai
On behalf of the co-authors
Citation: https://doi.org/10.5194/egusphere-2024-588-RC2
-
AC1: 'Reply on RC2', Fanqian Meng, 04 May 2024
Status: closed
-
RC1: 'Comment on egusphere-2024-588', Anonymous Referee #1, 25 Mar 2024
This manuscript presents the calibration algorithms used for the ACDL lidar onboard the DQ-1 satellite, with the analysis of the 532 nm nighttime polarization and high-spectral-resolution channels. This work is of interest to the lidar community. Also, the upcoming launch of EarthCARE with the ATLID lidar in May 2024 will provide opportunity for further comparative studies between these two advanced lidar systems. I appreciate the efforts made in this study and offer some comments for improvement of this manuscript. Additionally, a careful review of the manuscript for English language improvements is advised, as some sections may benefit from further editing for clarity and grammatical accuracy.
General comments:
- Figure 4: The blue dotted line is indistinguishable from other color curves representing iodine vapor absorption. Please enhance the figure’s visualization quality for better interpretation.
- Figure 7 (a): The large variation in original signals within the SAA region is noticeable, but the overlay of filtered signals obscures the original data in most other regions. Adjusting the transparency level of the filtered data may resolve this issue. This recommendation applies to all subplots in Figure 7.
- Figure 7 (c): There appears to be a discrepancy in the upper left legend; it likely should be labeled as “Parallel Channel” rather than “HSRL channel.”
- The error analysis in this manuscript provides a foundation for assessing calibration accuracy. Can the authors discuss how these error metrics compare with those from other missions or standards in atmospheric lidar measurements, which can offer readers a benchmark for assessing ACDL's performance?
- The manuscript mentions that ACDL data used in the paper are not publicly available. Given the scientific community's growing emphasis on open data for reproducibility and further analysis, consider discussing plans for data availability or establishing a data repository with access protocols, potentially making a portion of the data available.
- The aothors mentioned the plans for further validation tests. Can the authors expand on these plans, perhaps by detailing the types of lidar or other atmospheric sensors against which ACDL's data will be validated?
Technical comments:
- Lines 74-75: Simplify “with selected chose the region…” to “chose the region…” to enhance clarity.
- Lines 80-82: Include the name of the lidar instrument onboard EarthCARE: the ATLID (Atmospheric Lidar).
- Line 139: Suggest rephrasing for clarity: "Defining the normalized signals is a necessary first step for the different channels including:"
- Line 151: Align the order of terms (molecular, ozone, aerosol) with their presentation in Eq(5).
- Line 170: selects 31 -35 km as “the” calibration regions.
- Line 171: Clarification needed – replace “subsection” with “the following paragraphs” if subsections are not explicitly defined.
- Line 182: This sentence is unclear, please rephrase.
- Line 197: If available, include more recent references regarding this lidar ratio selection.
- Line 208: Ensure consistency in the order of terms as previously mentioned.
- Line 285: Correct to “Eq. (26) is” since only one equation is referenced.
- Line 289: Please provide details on defining the empirical scaling factor km, including the specific factor used in this study.
- Figure 7: The subfigure labels (a)(b)(c)(d) are missing or unclear.
- Line 328: Eqs. (32) and (33) are mentioned prematurely; they are introduced in the subsequent section.
- Line 370: A delta symbol is missing before PGR; please verify.
- Line 391: Amend to “can also be assessed” for grammatical accuracy.
Citation: https://doi.org/10.5194/egusphere-2024-588-RC1 -
AC2: 'Reply on RC1', Fanqian Meng, 04 May 2024
Dear Reviewer,
Many thanks for reviewing our manuscript. We greatly appreciate the substantial amount of time and effort that you dedicated to this review process.
We have revised the manuscript according to your comments point-to-point and the response is presented below as the supplement.
Many thanks and best regards.
Fanqian Meng, Junwu Tang and Guangyao Dai
On behalf of the co-authors
Citation: https://doi.org/10.5194/egusphere-2024-588-RC1
-
RC2: 'Comment on egusphere-2024-588', Anonymous Referee #2, 07 Apr 2024
-
AC1: 'Reply on RC2', Fanqian Meng, 04 May 2024
Dear Reviewer,
Many thanks for reviewing our manuscript. We greatly appreciate the substantial amount of time and effort that you dedicated to this review process.
We have revised the manuscript according to your comments point-to-point and the response is presented below as the supplement.
Many thanks and best regards.
Fanqian Meng, Junwu Tang and Guangyao Dai
On behalf of the co-authors
Citation: https://doi.org/10.5194/egusphere-2024-588-RC2
-
AC1: 'Reply on RC2', Fanqian Meng, 04 May 2024
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