Daily aerosol variation revealed by synergetic multi-satellite GRASP retrieval

In this study, we analyze the daily aerosol variability from synergetic multi-satellite GRASP retrieval. On a regional to local scale, aerosol diurnal concentration and microphysical properties can change rapidly due to inherent short lifespan, intense source emissions and weather processes. To observe the aerosol diurnal variability of a region, it is necessary to have multiple satellite measurements (greater than two measurements per day), and desirable to have per-hour satellite measurement. The capability to observe aerosol diurnal patterns is of interest to many research and applications such as: basic research of the aerosol global spatial distribution, variability and climate effects; aerosol transport modelling; Assimilation into atmospheric circulation models, etc. To meet these needs, it is essential to utilize all available satellite measurements to increase the sampling in time, in scattering angle and in spectral space.

 

In the ESA SYREMIS project, we performed a pioneering attempt of synergetic retrieval combining OLCI/Sentinel-3(A and B), TROPOMI/Sentinel-5p and AHI/Himawari-8 measurements using the GRASP algorithm. Such synergy of instruments from different satellite platforms greatly expands the spectral range, observation angle range and temporal observation density compared to existing synergy/merged satellite products. This led to much enhanced observation capability and retrieval accuracy for the merged instrument network. Among the aerosol products from synergetic retrieval, Aerosol Optical Depth (AOD) show very good fit to AERONET AOD diurnal time series, aerosol microphysical parameters such as Angstrom Exponent (AE) and Single Scattering Albedo (SSA) also show very good fit to the corresponding AERONET diurnal time series. Lateral comparison with the XAERDT merged aerosol products (MODIS+VIIRS+AHI) were made, and GRASP synergetic aerosol products show superior performance, especially in terms of the temporal stability of all aerosol parameters, and accuracy of the aerosol microphysical parameters. The improved synergy aerosol product should greatly benefit downstream applications such as aerosol transport modelling, assimilation into atmospheric circulation models and air quality forecast models.