Combined Retrieval from Ground Based and Space-borne Measurements: New Possibilities for Surface Validation and Beyond

During a few last decades AERONET direct measurement and inversion products are the main validation dataset for satellite aerosol retrieval. Together with aerosol, Earth surfaces are the major contributor to the climate. Moreover, correct surface reflectance description is also a crucial component of any satellite aerosol retrieval algorithm. Despite of evident need of the universal and robust reference dataset for surface, it still does not exist.

Available ground-based measurements of the surface albedo/reflectance or BRDF in worldwide location may not be universal tool for satellite surface product validation due to the fact that Earth surfaces, as a rule, are very spatially heterogeneous. Moreover, ground-based and satellite measurements can be performed in different spectral channels.

Satellite surface products may suffer from aerosol contamination or lack of multi-angle measurements for BRDF characterisation. Their usage for surface validation always raises a question about accuracy and uncertainties. The first real attempt to create operational processing system for surface validation was realized in ASRVN (AERONET-based surface reflectance validation network) dataset where the atmospheric correction of MODIS measurements was performed using AERONET aerosol products.

Further essential enhancement of the surface retrieval accuracy, as well as its unification, can be achieved by inverting simultaneously AERONET and satellite measurements to retrieval of aerosol and surface properties. This approach looks rather robust and universal for being applied to any space-borne instruments independently of spatial resolution or information content (for any spectral bands, radiance only or polarimeter, single or multiple view instruments). It has already been implemented in the frame of GRASP retrieval developments further strengthening from the use of multi-pixel approach and advanced retrieval scheme. Thus, here we present the concept of such combined "AERONET plus satellite" retrieval and discuss first result of surface reference dataset obtained from diverse space-borne instruments like PARASOL, S5P/TROPOMI, S2 and S3/OLCI.