ACIX: Atmospheric Correction Inter-comparison Exercise

Surface reflectance is one of the key products used in developing several higher-order land products. Understanding and characterizing the uncertainties of surface reflectance is critical for downstream users. The purpose of ACIX is to inter-compare the performance of 14 atmospheric processors from five different countries for the Landsat8 OLI and Sentinel 2 MSI data. The exercise is expected to point out the strengths and weaknesses as well as the commonalities and differences of the different atmospheric correction processors with aim to enable further improvements. A carefully crafted protocol for the inter-comparison and the test dataset focused on the AERONET sites will be described, according to what was agreed during the first ACIX workshop held in June 2016. The protocol includes the comparison of aerosol optical thickness and water vapor products of the processors with the AERONET measurements.. Concerning the surface reflectances, the protocol describes the inter-comparison among the processors, as well as the comparison with the MODIS surface reflectance and with a reference surface reflectance product. Such a reference product will be obtained using the AERONET characterization of the aerosol (size distribution and refractive indices) and an accurate radiative transfer code. We will present the first results and lessons learned from the first phase of this exercise.