1. Does CALIPSO have a higher sensitivity to aerosols in the free troposphere (FT)? When I calculate the AOD by the annual mean extionction coefficient profiles, the results are almost twice as much as the AOD provided by CALIPSO directly. So I'm not sure if CALIPSO >PBL AOD is biased high.
2. The valid range for extinction coefficient is 0.0...1.25, but when I calculated AOD by the profile and compared with AOD provided by CALIPSO directly, I found the the AOD products take all the extinction coefficients into consideration no matter it is larger than 1.25 or not. So are the extinction coefficients larger than 1.25 also valid?
Overestimation for CALIPSO AOD in the free troposphere?
-
yuzheng0835380
- Posts: 1
- Joined: Sat Jul 05, 2025 2:42 am America/New_York
Overestimation for CALIPSO AOD in the free troposphere?
- Attachments
-
- For Q2.
- valid_range.png (202.38 KiB) Not viewed yet
-
- For Q1: The comparison of AOD
- AOD_North_China.png (128.02 KiB) Not viewed yet
-
- For Q1: The profiles of extinction coefficient
- profile.png (35.26 KiB) Not viewed yet
Filters:
Re: Overestimation for CALIPSO AOD in the free troposphere?
[Q] does CALIPSO have a higher sensitivity to aerosols in the free troposphere?
[A] for a fixed aerosol attenuated backscatter magnitude, CALIOP’s detection sensitivity would be better at higher altitudes simply because the contrast between the aerosol and the ambient molecular atmosphere will be higher.
[Q] When I calculate the AOD by the annual mean extinction coefficient profiles, the results are almost twice as much as the AOD provided by CALIPSO directly. So I’m not sure if CALIPSO >PBL AOD is biased high.
[A] without knowing much, much more about which data products you’re using (e.g., level 2 layer products? level 2 profile products? level 3? all of the above?), how you constructed your comparisons, and what (if any) quality assurance filtering you applied, it’s impossible to offer any specific guidance. but, in general, no, CALIPSO’s AOD in the free troposphere is not biased high; e.g., see Bourgeois et al., 2018 (https://doi.org/10.5194/acp-18-7709-2018) and the error analyses conducted in Thorsen et al., 2025 (https://doi.org/10.1029/2024JD042416).
[Q] The valid range for extinction coefficient is 0.0...1.25, but when I calculated AOD by the profile and compared with AOD provided by CALIPSO directly, I found the AOD products take all the extinction coefficients into consideration no matter it is larger than 1.25 or not. So are the extinction coefficients larger than 1.25 also valid?
[A] yes, long, long ago we made an unfortunate and misleading choice when specifying the “valid range” for the CALIOP aerosol extinction coefficients. and you’re correct in noting that values larger than 1.25 km–1 (and values less than 0 km–1) can be treated as valid in the AOD retrievals. to determine whether a specific retrieval is or is not valid, refer to the extinction QC flags, reported in both the layer products and the profile products. documentation for these flags is available in the CALIPSO users’ guide (https://www-calipso.larc.nasa.gov/resources/calipso_users_guide/data_desc/cal_lid_l2_profile_v4-51_desc.php#extinction_qc_flag_532) and/or in Young et al., 2018 (https://doi.org/10.5194/amt-11-5701-2018). extinction retrievals should be considered bad if any of bits 2, 3, 5, 7–12, or 14 are set. (this specification uses 0-based indexing with bit 0 being the least significant.)
[A] for a fixed aerosol attenuated backscatter magnitude, CALIOP’s detection sensitivity would be better at higher altitudes simply because the contrast between the aerosol and the ambient molecular atmosphere will be higher.
[Q] When I calculate the AOD by the annual mean extinction coefficient profiles, the results are almost twice as much as the AOD provided by CALIPSO directly. So I’m not sure if CALIPSO >PBL AOD is biased high.
[A] without knowing much, much more about which data products you’re using (e.g., level 2 layer products? level 2 profile products? level 3? all of the above?), how you constructed your comparisons, and what (if any) quality assurance filtering you applied, it’s impossible to offer any specific guidance. but, in general, no, CALIPSO’s AOD in the free troposphere is not biased high; e.g., see Bourgeois et al., 2018 (https://doi.org/10.5194/acp-18-7709-2018) and the error analyses conducted in Thorsen et al., 2025 (https://doi.org/10.1029/2024JD042416).
[Q] The valid range for extinction coefficient is 0.0...1.25, but when I calculated AOD by the profile and compared with AOD provided by CALIPSO directly, I found the AOD products take all the extinction coefficients into consideration no matter it is larger than 1.25 or not. So are the extinction coefficients larger than 1.25 also valid?
[A] yes, long, long ago we made an unfortunate and misleading choice when specifying the “valid range” for the CALIOP aerosol extinction coefficients. and you’re correct in noting that values larger than 1.25 km–1 (and values less than 0 km–1) can be treated as valid in the AOD retrievals. to determine whether a specific retrieval is or is not valid, refer to the extinction QC flags, reported in both the layer products and the profile products. documentation for these flags is available in the CALIPSO users’ guide (https://www-calipso.larc.nasa.gov/resources/calipso_users_guide/data_desc/cal_lid_l2_profile_v4-51_desc.php#extinction_qc_flag_532) and/or in Young et al., 2018 (https://doi.org/10.5194/amt-11-5701-2018). extinction retrievals should be considered bad if any of bits 2, 3, 5, 7–12, or 14 are set. (this specification uses 0-based indexing with bit 0 being the least significant.)