An Enhanced Aerosol Optical Depth Retrieval Algorithm for Particulate Observing Scanning Polarimeter (POSP) Data over Land

Single-angle sensors typically utilize radiative trans-
fer simulations based on Lambertian surface, even though the sur-
face reflectance obtained exhibits directional characteristics. Fully
accounting for the contribution of surface directional characteris-
tics to the Top of atmosphere (TOA) reflectances can further im-
prove the accuracy of aerosol retrievals. In this study, we propose
an enhanced aerosol retrieval algorithm for the Particulate Ob-
serving Scanning Polarimeter (POSP), by further considering the
surface directional characteristics. Combined with an updated
aerosol model, this approach achieves high-accuracy retrievals.
We used historical Bidirectional Reflectance Distribution Func-
tion (BRDF) products to construct stable surface constraints. By
exploring the strong empirical statistical relationships between ad-
jacent blue bands, we have realized the joint inversion of multiple
blue bands. Additionally, we employed an optimization algorithm
that incorporates boundary constraints, simultaneously account-
ing for errors in the surface constraint model, and satellite obser-
vation errors. The global aerosol optical thickness (AOD) at
550nm over land was retrieved from November 2021 to April 2022.
Validation of POSP AOD versus AErosol RObotic NETwork
(AERONET) data shows a high consistency, with correlation coef-
ficient (R) of 0.93, root mean square error (RMSE) of 0.086, bias
of 0.004, fraction within expected error (EE) of 80.8%, and frac-
tion within Global Climate Observing System (GCOS) of 52.1%.
Comparison with MODIS aerosol products shows that the accu-
racy of POSP AOD is better than that of MODIS AOD. According
to the matching results, for DB, R of 0.936/0.907, fraction within
EE of 82.2%/74.9% (POSP/MODIS DB); for DT, R of 0.937/0.915,
fraction within EE of 83.5%/ 72.0% (POSP/MODIS DT). The spa-
tial distribution difference between POSP AOD and DB AOD is
small, indicating good consistency, and POSP AOD captured the
intensity of aerosol pollution well. In summary, the enhanced aer-
osol algorithm achieves reliable high-precision AOD retrieval and
because of its generality could also be applied to other sensors.