the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 20 Oct 2023
Aerosol Optical Properties Measurement using the Orbiting High Spectral Resolution Lidar onboard DQ-1 Satellite: Retrieval and Validation
Abstract. The atmospheric environment monitoring satellite DQ-1 was launched in April 2022, which consists of a spaceborne High Spectral Resolution Lidar (HSRL) system. This new system enables the accurate measurements of global aerosol optical properties, which can be used in Geo-scientific community after the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) retirement. Developing a suitable retrieval algorithm and validating retrieved results are prominently needed. This research demonstrates a retrieval algorithm for aerosol optical properties using the DQ-1 HSRL system. This method has retrieved the aerosol depolarization ratio, backscatter coefficient, extinction coefficient, and optical depth. For validation purposes, we compared retrieved results with those obtained through CALIPSO. The results have shown a continuous profile alignment between the two datasets, with DQ-1 describing an improved signal-to-noise ratio of approximately 10 dB. Optical property profiles from NASA Micro Pulse Lidar NETwork (MPLNET) stations were selected for validation with the DQ-1 measurements, resulting in a relative error of 25 %. Between June 2022 and December 2022, aerosol optical depth measurements using the DQ-1 satellite and the AErosol RObotic NETwork (AERONET) were correlated and yielded a value of R2 0.803. We use the DQ-1 dataset to initially investigate the transport processes of the Saharan dust and the South Atlantic volcanic ash. These validations and applications show that the DQ-1 HSRL system can accurately measure global aerosols and holds significant prospects for earth science applications.
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CC1: 'Comment on amt-2023-219', Albert Ansmann, 08 Nov 2023
The manuscript describes the performance of the Chinese aerosol space lidar DQ-1 HSRL. This manuscript will be probably one of the fundamental papers on  DQ-1 HSRL. Therefore, the quality of the manuscript must be improved. Much more information about the quality of the measured signals, about calibration and quality assurance efforts, about cross talk in the different measurement channels needs to be provided.
Major revision is thus recommended.
Detailed comments:
Abstract:
What is the meaning of DQ-1 (DQ stands for…?, should be explained…).
I would suggest not to use dB to characterize signal-to-noise ratios or the cross talk impact. Just use signal ratios such as P1/P2 instead of Q = 10 log (P1/P2) in dB.
In the abstract, R^2 0.803, you mean R^2=0.803?Â
Introduction
line 53: The shortcomings of airborne (and spaceborne) observations could also be mentioned: They deliver snapshot-like observations, compared to ground-based (GB) observations. GB remote sensing may allow to study life cycle processes, evolutions, developments.
lines 66-68: The text is confusing, please rephrase!. Furthermore, one could mention other activities such as the AEOLUS and the EarthCARE space lidar missions, in support to CALIPSO.
line 79: … to be launched…when?
line 82: What does DQ mean? Please explain!
Instrumentation and method
line 112: There are three signal channels: cross-polarized (particle+Rayleigh), co-polarized (particle+Rayleigh), and HSRL channel (Rayleigh). Please add this information on particles and Rayleigh contributions.
line 117: You mention, the aerosol suppression ratio is more than 25 dB. So, we have less than  -25 dB, i.e., less than 0.00316). Is that sufficient to derive extinction profiles? In the case of cirrus backscatter and extinction, you may need 5-6 orders of magnitude suppression to obtain high-quality extinction profiles? But maybe you correct for cross talk? But that should then be explicitly described.
DQ-1 detects co and cross-polarized Rayleigh and particle backscatter components. We need to know, how large the contribution of these four signal components is in the three measurement channels? Is all the cross talk considered and corrected for in the different product retrievals? How are the transmission and reflection properties of the optical elements in the receiver unit, between the telescope  and the detector. What is the contribution of the four signal elements to the detected signal counts in the three channels.
All potential cross talk effects must be considered in the retrieval. So, please discuss the contribution of the four backscatter components in the three channels.
The Eqs.(2.1)-(2.3) are too simple! No efficiency factor (describing optical and detection efficiency), no cross talk factor!
An Eq.( ) for T_m would be nice.
Please state in the mansucript where you found Eq.(2.4).
So, Eq.(2.5) does not need any calibration? The depolarization ratio is simply obtained from the ratio of the cross- to- co-polarized channel outputs?
Please provide a reference for Eq.(2.6)!
Two times the same equation: Eq.(2.6) and Eq.(2.8).
Please, provide reference for Eq.(2.9). What is the solution for Eq.(2.9) if you start fromEq.(2.8) (or Eq.(2.6))? Â
line 175: Please explain all abbreviations when they appear for the first time!
line 184:Â Pappalardo et al. (2014) deal with the EARLINET lidar network, not with the MPLNET.
line 191: For HYSPLIT we need a references.
Validation of the retrieval results
line 227:  … with a 10^-4 m^-1 values …. What does it mean? What do you want to tell us?
line 228:  … with a value of 10^-5 m^-1 sr^-1. …. What does it mean? What do you want to tell us?
lines 222 and 234: the same … I do not understand!
line 245: CALIPSO does not measure the lidar ratio! The lidar ratio is an input value in the CALIPSO data analysis. The lidar ratio has to be set! Note,the lidar ratio dimension is sr and not sr^-1.
line 247: In case of CALIPSO measurements of marine particles the lidar ratio is set to 20 sr. The dimension sr^-1 is wrong.
What about the measured lidar ratios (DQ-1 HSRL), measured within the cirrus at 15 km height? Please discuss the values. This is one of the important new products of a spaceborne HSRL, compared to the CALIPSO products. Should be highlighted!
Regarding cirrus and specular reflection! Is the lidar zenith or off-zenith pointing?
MPL is an elastic backscatter lidar as the CALIPSO lidar. This lidar type only delivers profiles for the backscatter coefficient. This lidar cannot measure extinction coefficients and lidar ratios.
line 281: At the end of the section, what about the lidar ratios measured with the DQ-1 lidar?
line 313: You mean top height of 8 km or base height of 8 km? Please, specify.
line 320: You may also check these papers regarding long range transport towards the Caribbean:
Haarig et al., Atmos. Chem. Phys., 17, https://doi.org/10.5194/acp-17-10767-2017
Rittmeister et al., Atmos. Chem. Phys., 17, https://doi.org/10.5194/acp-17-12963-2017
Ansmann et al., Atmos. Chem. Phys., 17, https://doi.org/10.5194/acp-17-14987-2017
Section 4: Why not showing height profiles of extinction, depolarization ratio, and lidar ratio in addition.
Figure 1: One should indicate the different channels (B, B_C, B_H)
Figure 4e: Please mention that mean profiles for 20-22°N (longitudes…?) are shown.
Figure 5: the color range should be improved. We have mostly dark blue, sometimes light blue (or cyan) and sometimes yellow. The advantage of DQ-1 HSRL is that lidar ratios can be measured. But lidar ratio results are not shown in Figure 5 (i:backscatter, j: extinction, why not k: lidar ratio). and also, what about depolarization ratio results?
Figure 6: MPL retrievals can only deliver particle backscatter profiles. If extinction profiles obtained with MPL and DQ-1 HSRL match then this is just the hint that the lidar ratio was around 50 sr, as assumed in the MPL retrieval. What about depolarization profiles.
Figure 7: Again, only backscatter can be compared.
Citation: https://doi.org/10.5194/amt-2023-219-CC1 -
AC1: 'Reply on CC1', Jim Hsing, 27 Dec 2023
We greatly appreciate Dear Dr. Albert Ansmann’s valuable time reviewing our research paper and providing feedback/suggestions. The comments are valuable and helpful for improving our paper. We have studied all comments carefully and have made major revisions to our manuscript. Please see the attachment.
-
AC1: 'Reply on CC1', Jim Hsing, 27 Dec 2023
-
RC1: 'Comment on amt-2023-219', Anonymous Referee #1, 28 Dec 2023
The manuscript describes a first validation of DQ-1 HSRL aerosol measurements by comparing to CALIPSO, MPLNET and AERONET measurements. DQ-1 HSRL is very important as it follows the CALISPO satellite and thus maintain long-term global aerosol and cloud profiling measurements. Thus, a proper validation is of major importance. However, this paper needs major revisions prior to publication. Besides the need of technical processing (language editing), essential information on the calibration, especially with regard to depolarization measurements, the quality assurance and the quality of the measurements is missing. Â
Specific comments:
Abstract: DQ-1 consists of more than just the lidar
Abstract: Linear depolarization ratio?
P.1, l. 30: Probably 10^2 is meant here. 10 nm as maximum is certainly wrong. And in principle there is no lower limit until you reach the molecular level at about 0.1 nm.
P.2, l. 38: I would not assume results from ground-based lidar systems to be more accurate in general. Especially when e.g. assuming daytime measurements with Fernald/Klett algorithms and no further information of the lidar ratio or the long integration time needed for night-time Raman measurements. Also compared to what; airborne or spaceborne measurements?
P.2, l. 39: ‘Additionally, comparing…’ This sentence seems to be at the wrong place here.
P.3, l. 65: Was fuel consumption really the reason? I also heard of solar panel degradation. Maybe you should add a reference.
P.3, l. 73: According to the latest developments AOS will not incorporate an HSRL channel. But this may change again if NASA sees the benefit of the DQ-1 data.
P.3, l. 83: Does duel-polarization mean duel wavelength?
P.4, l. 108: To which line catalogue corresponds this numbering? Please give a reference.
P.4, l. 110: What exactly is meant by 'categorized' and 'adjusted' here?
P.4, l. 118: 25 db is quite low for a J2 filter. Is this limited by the iodine vapor pressure or is there some spectral impurity of the laser? And how stable is this value, as it has to be considered in the retrieval?
P.4, l.125: ‘A and B…’ It is not exactly clear what is meant here with interleaved.
P.4, l. 125: compare = achieve?
P.6, Eq 2.8: This is a replication of Eq. 2.6. Please delete.
P.8, l. 215: There seems to something wrong with the CALIPSO backscatter profile! See remark at the plot!
P.8, l. 236f: Why should this be a mixture, here directly of the desert? In the retrieval the dust plume looks extremely homogenous, with no sign of mixing.
P.8, l. 243ff: What is meant here by laser energy attenuation? A smaller laser energy does not alter the mean profile.
P.8, l.245: For CALIPSO this value comes from a database and is not measured. And 50 sr does not really point to mixed dust.
P.9, l. 256: The sentence says the same as the previous one.
P.11, l. 319: Particle depolarization ratio would be much more valuable.
P.11, l., 320: If this is volume depolarization ratio, like stated above, this is not necessarily the case. The constant lidar ratio does not indicate a large amount of mixing. Please provide aerosol particle depolarization. Maybe in the instrument section a paragraph should be added on how the depolarization measurements are calibrated and how large a possible instrument related depolarization is.
P.11, l.333: The backscatter coefficient does not depend on laser energy, only the raw signals. So, there is nothing to correct.
P.12, l. 344: I would recommend to talk of volcanic aerosol not volcanic ash. The ash sediments out quite fast. What goes into the stratosphere are mostly condensated gases like H2O or H2SO4 etc.
P.13, l. 353: It has not been shown that the outcome of the depolarization ratio from DQ-1 is more reliable. No analyses of the systematical error of the depolarization measurements have been provided.
P.22, Figure 4: The profile (e) for Calipso seems wrong and also does not fit to the data given in the 2d plot (b). In the profile plot (e) the data of Calipso drops below 10^-5 above 14 km. But this behavior is not present in (b) where ist stays between 10^-3 to 10^-4.
P.29, Figure 9: The figures are too small to see all details. I would suggest to put them below each other and enlarge them to fill the whole page width. What sort of depolarization ration is shown? According to the main text it is volume depolarization but particle depolarization would be more interesting.
P.30, Table 1: What is missing here is the optical efficiency of the receiver optics including sun-light filter and the quantum efficiency of the detector. The measurement accuracy depends on the atmosphere probed, i.e. on altitude and aerosol content and also on ambient light conditions. So, one number is not characterizing this well. Furthermore, horizontal resolution would be a better wording than parallel resolution
Citation: https://doi.org/10.5194/amt-2023-219-RC1 - AC2: 'Reply on RC1', Jim Hsing, 14 Jan 2024
-
RC2: 'Comment on amt-2023-219', David Winker, 18 Jan 2024
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2023-219/amt-2023-219-RC2-supplement.pdf
-
AC3: 'Reply on RC2', Jim Hsing, 14 Feb 2024
We greatly appreciate Dr. David Winker’s valuable time reviewing our manuscript and providing feedback/suggestions. The comments are valuable and helpful for improving our manuscript. We have studied all comments carefully and have made revisions to our manuscript. Please see the attachment.
-
AC3: 'Reply on RC2', Jim Hsing, 14 Feb 2024
Status: closed
-
CC1: 'Comment on amt-2023-219', Albert Ansmann, 08 Nov 2023
The manuscript describes the performance of the Chinese aerosol space lidar DQ-1 HSRL. This manuscript will be probably one of the fundamental papers on  DQ-1 HSRL. Therefore, the quality of the manuscript must be improved. Much more information about the quality of the measured signals, about calibration and quality assurance efforts, about cross talk in the different measurement channels needs to be provided.
Major revision is thus recommended.
Detailed comments:
Abstract:
What is the meaning of DQ-1 (DQ stands for…?, should be explained…).
I would suggest not to use dB to characterize signal-to-noise ratios or the cross talk impact. Just use signal ratios such as P1/P2 instead of Q = 10 log (P1/P2) in dB.
In the abstract, R^2 0.803, you mean R^2=0.803?Â
Introduction
line 53: The shortcomings of airborne (and spaceborne) observations could also be mentioned: They deliver snapshot-like observations, compared to ground-based (GB) observations. GB remote sensing may allow to study life cycle processes, evolutions, developments.
lines 66-68: The text is confusing, please rephrase!. Furthermore, one could mention other activities such as the AEOLUS and the EarthCARE space lidar missions, in support to CALIPSO.
line 79: … to be launched…when?
line 82: What does DQ mean? Please explain!
Instrumentation and method
line 112: There are three signal channels: cross-polarized (particle+Rayleigh), co-polarized (particle+Rayleigh), and HSRL channel (Rayleigh). Please add this information on particles and Rayleigh contributions.
line 117: You mention, the aerosol suppression ratio is more than 25 dB. So, we have less than  -25 dB, i.e., less than 0.00316). Is that sufficient to derive extinction profiles? In the case of cirrus backscatter and extinction, you may need 5-6 orders of magnitude suppression to obtain high-quality extinction profiles? But maybe you correct for cross talk? But that should then be explicitly described.
DQ-1 detects co and cross-polarized Rayleigh and particle backscatter components. We need to know, how large the contribution of these four signal components is in the three measurement channels? Is all the cross talk considered and corrected for in the different product retrievals? How are the transmission and reflection properties of the optical elements in the receiver unit, between the telescope  and the detector. What is the contribution of the four signal elements to the detected signal counts in the three channels.
All potential cross talk effects must be considered in the retrieval. So, please discuss the contribution of the four backscatter components in the three channels.
The Eqs.(2.1)-(2.3) are too simple! No efficiency factor (describing optical and detection efficiency), no cross talk factor!
An Eq.( ) for T_m would be nice.
Please state in the mansucript where you found Eq.(2.4).
So, Eq.(2.5) does not need any calibration? The depolarization ratio is simply obtained from the ratio of the cross- to- co-polarized channel outputs?
Please provide a reference for Eq.(2.6)!
Two times the same equation: Eq.(2.6) and Eq.(2.8).
Please, provide reference for Eq.(2.9). What is the solution for Eq.(2.9) if you start fromEq.(2.8) (or Eq.(2.6))? Â
line 175: Please explain all abbreviations when they appear for the first time!
line 184:Â Pappalardo et al. (2014) deal with the EARLINET lidar network, not with the MPLNET.
line 191: For HYSPLIT we need a references.
Validation of the retrieval results
line 227:  … with a 10^-4 m^-1 values …. What does it mean? What do you want to tell us?
line 228:  … with a value of 10^-5 m^-1 sr^-1. …. What does it mean? What do you want to tell us?
lines 222 and 234: the same … I do not understand!
line 245: CALIPSO does not measure the lidar ratio! The lidar ratio is an input value in the CALIPSO data analysis. The lidar ratio has to be set! Note,the lidar ratio dimension is sr and not sr^-1.
line 247: In case of CALIPSO measurements of marine particles the lidar ratio is set to 20 sr. The dimension sr^-1 is wrong.
What about the measured lidar ratios (DQ-1 HSRL), measured within the cirrus at 15 km height? Please discuss the values. This is one of the important new products of a spaceborne HSRL, compared to the CALIPSO products. Should be highlighted!
Regarding cirrus and specular reflection! Is the lidar zenith or off-zenith pointing?
MPL is an elastic backscatter lidar as the CALIPSO lidar. This lidar type only delivers profiles for the backscatter coefficient. This lidar cannot measure extinction coefficients and lidar ratios.
line 281: At the end of the section, what about the lidar ratios measured with the DQ-1 lidar?
line 313: You mean top height of 8 km or base height of 8 km? Please, specify.
line 320: You may also check these papers regarding long range transport towards the Caribbean:
Haarig et al., Atmos. Chem. Phys., 17, https://doi.org/10.5194/acp-17-10767-2017
Rittmeister et al., Atmos. Chem. Phys., 17, https://doi.org/10.5194/acp-17-12963-2017
Ansmann et al., Atmos. Chem. Phys., 17, https://doi.org/10.5194/acp-17-14987-2017
Section 4: Why not showing height profiles of extinction, depolarization ratio, and lidar ratio in addition.
Figure 1: One should indicate the different channels (B, B_C, B_H)
Figure 4e: Please mention that mean profiles for 20-22°N (longitudes…?) are shown.
Figure 5: the color range should be improved. We have mostly dark blue, sometimes light blue (or cyan) and sometimes yellow. The advantage of DQ-1 HSRL is that lidar ratios can be measured. But lidar ratio results are not shown in Figure 5 (i:backscatter, j: extinction, why not k: lidar ratio). and also, what about depolarization ratio results?
Figure 6: MPL retrievals can only deliver particle backscatter profiles. If extinction profiles obtained with MPL and DQ-1 HSRL match then this is just the hint that the lidar ratio was around 50 sr, as assumed in the MPL retrieval. What about depolarization profiles.
Figure 7: Again, only backscatter can be compared.
Citation: https://doi.org/10.5194/amt-2023-219-CC1 -
AC1: 'Reply on CC1', Jim Hsing, 27 Dec 2023
We greatly appreciate Dear Dr. Albert Ansmann’s valuable time reviewing our research paper and providing feedback/suggestions. The comments are valuable and helpful for improving our paper. We have studied all comments carefully and have made major revisions to our manuscript. Please see the attachment.
-
AC1: 'Reply on CC1', Jim Hsing, 27 Dec 2023
-
RC1: 'Comment on amt-2023-219', Anonymous Referee #1, 28 Dec 2023
The manuscript describes a first validation of DQ-1 HSRL aerosol measurements by comparing to CALIPSO, MPLNET and AERONET measurements. DQ-1 HSRL is very important as it follows the CALISPO satellite and thus maintain long-term global aerosol and cloud profiling measurements. Thus, a proper validation is of major importance. However, this paper needs major revisions prior to publication. Besides the need of technical processing (language editing), essential information on the calibration, especially with regard to depolarization measurements, the quality assurance and the quality of the measurements is missing. Â
Specific comments:
Abstract: DQ-1 consists of more than just the lidar
Abstract: Linear depolarization ratio?
P.1, l. 30: Probably 10^2 is meant here. 10 nm as maximum is certainly wrong. And in principle there is no lower limit until you reach the molecular level at about 0.1 nm.
P.2, l. 38: I would not assume results from ground-based lidar systems to be more accurate in general. Especially when e.g. assuming daytime measurements with Fernald/Klett algorithms and no further information of the lidar ratio or the long integration time needed for night-time Raman measurements. Also compared to what; airborne or spaceborne measurements?
P.2, l. 39: ‘Additionally, comparing…’ This sentence seems to be at the wrong place here.
P.3, l. 65: Was fuel consumption really the reason? I also heard of solar panel degradation. Maybe you should add a reference.
P.3, l. 73: According to the latest developments AOS will not incorporate an HSRL channel. But this may change again if NASA sees the benefit of the DQ-1 data.
P.3, l. 83: Does duel-polarization mean duel wavelength?
P.4, l. 108: To which line catalogue corresponds this numbering? Please give a reference.
P.4, l. 110: What exactly is meant by 'categorized' and 'adjusted' here?
P.4, l. 118: 25 db is quite low for a J2 filter. Is this limited by the iodine vapor pressure or is there some spectral impurity of the laser? And how stable is this value, as it has to be considered in the retrieval?
P.4, l.125: ‘A and B…’ It is not exactly clear what is meant here with interleaved.
P.4, l. 125: compare = achieve?
P.6, Eq 2.8: This is a replication of Eq. 2.6. Please delete.
P.8, l. 215: There seems to something wrong with the CALIPSO backscatter profile! See remark at the plot!
P.8, l. 236f: Why should this be a mixture, here directly of the desert? In the retrieval the dust plume looks extremely homogenous, with no sign of mixing.
P.8, l. 243ff: What is meant here by laser energy attenuation? A smaller laser energy does not alter the mean profile.
P.8, l.245: For CALIPSO this value comes from a database and is not measured. And 50 sr does not really point to mixed dust.
P.9, l. 256: The sentence says the same as the previous one.
P.11, l. 319: Particle depolarization ratio would be much more valuable.
P.11, l., 320: If this is volume depolarization ratio, like stated above, this is not necessarily the case. The constant lidar ratio does not indicate a large amount of mixing. Please provide aerosol particle depolarization. Maybe in the instrument section a paragraph should be added on how the depolarization measurements are calibrated and how large a possible instrument related depolarization is.
P.11, l.333: The backscatter coefficient does not depend on laser energy, only the raw signals. So, there is nothing to correct.
P.12, l. 344: I would recommend to talk of volcanic aerosol not volcanic ash. The ash sediments out quite fast. What goes into the stratosphere are mostly condensated gases like H2O or H2SO4 etc.
P.13, l. 353: It has not been shown that the outcome of the depolarization ratio from DQ-1 is more reliable. No analyses of the systematical error of the depolarization measurements have been provided.
P.22, Figure 4: The profile (e) for Calipso seems wrong and also does not fit to the data given in the 2d plot (b). In the profile plot (e) the data of Calipso drops below 10^-5 above 14 km. But this behavior is not present in (b) where ist stays between 10^-3 to 10^-4.
P.29, Figure 9: The figures are too small to see all details. I would suggest to put them below each other and enlarge them to fill the whole page width. What sort of depolarization ration is shown? According to the main text it is volume depolarization but particle depolarization would be more interesting.
P.30, Table 1: What is missing here is the optical efficiency of the receiver optics including sun-light filter and the quantum efficiency of the detector. The measurement accuracy depends on the atmosphere probed, i.e. on altitude and aerosol content and also on ambient light conditions. So, one number is not characterizing this well. Furthermore, horizontal resolution would be a better wording than parallel resolution
Citation: https://doi.org/10.5194/amt-2023-219-RC1 - AC2: 'Reply on RC1', Jim Hsing, 14 Jan 2024
-
RC2: 'Comment on amt-2023-219', David Winker, 18 Jan 2024
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2023-219/amt-2023-219-RC2-supplement.pdf
-
AC3: 'Reply on RC2', Jim Hsing, 14 Feb 2024
We greatly appreciate Dr. David Winker’s valuable time reviewing our manuscript and providing feedback/suggestions. The comments are valuable and helpful for improving our manuscript. We have studied all comments carefully and have made revisions to our manuscript. Please see the attachment.
-
AC3: 'Reply on RC2', Jim Hsing, 14 Feb 2024
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