ACIX is an initiative to bring together the developers of Atmospheric Correction (AC) processors, who are invited to generate Bottom-Of-Atmosphere (BOA) products from Top-Of-Atmosphere (TOA) optical satellite data. The exercise is a collaborative activity of ESA (European Space Agency) and NASA (National Aeronautics and Space Administration) that initiated in 2016 in the frame of CEOS WGCV. ACIX has been already implemented twice on multispectral Copernicus Sentinel-2 and Landsat 8 imagery. More information on the latest analysis and the results can be found in the dedicated web pages for the Land- and Aqua-focused part of the exercise.

In parallel with ACIXs, a Cloud-Masking Inter-comparison exercise (CMIX) ran over specific areas with reference data available. Similarly to ACIXs, the focus of the first CMIX was on open and free imagery acquired by the Copernicus Sentinel-2 (EC/ESA) and Landsat 8 (NASA/USGS) missions. For more information on the first CMIX implementation can be found on https://calvalportal.ceos.org/cmix.

Considering the great scientific and users' interest, a third ACIX and second CMIX implementations are proposed involving also hyperspectral data this time. In collaboration with ASI (Agenzia Spaziale Italiana/ Italian Space Agency), PRISMA data have been acquired for the exercises' purposes mainly over sites in Europe and North America. Multispectral data of Sentinel-2 and Landsat 8 will still be part of the ACIX-Aqua and CMIX analysis. ACIX-Land though will focus only on PRISMA hyperspectral data, as it was considered unnecessary to repeat the exercise for multispectral data at the moment. The decision is mainly based on the unavailability of any new reference data to the ones used in the previous exercises. The exercises' implementation scheme is presented below:

The 1st WS of ACIX-III Land, Aqua and CMIX-II is foreseen to be held in ESA/ESRIN (Frascati, Italy) in Q2/2022, where coordinators and participants will discuss and define the implementation protocols. The rest of the milestones are shown below with the exact dates to be defined together with the participants.

Participation to ACIXs and CMIX is open to all the scientists who:

1. are the original developers of the atmospheric correction and/or cloud-masking processor to be inter-compared,
2. are authorized by the original developer to run the AC processor on his/her behalf,
3. agree on submitting the AC processing results within the required constraints (deadline, format, etc.).

If you are interested to participate in the ACIX and CMIX experiments, please write to Georgia.Doxani@esa.int, including your name, affiliation, exercise of interest, name of processor.