ACIX aims to bring together the developers of Atmospheric Correction (AC) processors, who are invited to generate the corresponding Bottom-Of-Atmosphere (BOA) products. The input data are Landsat-8 and Sentinel-2 imagery of various sites. A common and harmonised inter-comparison procedure is agreed and followed by all the participants.

The first ACIX experiment started in June 2016 with its description and conclusions to be summarised in Doxani et al. (2018). All the inter-comparison results can be found in the dedicated to ACIX I web page. ACIX I was completed in February 2018, but the improved versions of the participating processors and the increasing interest of AC developers to be part of the experiment stimulated the continuation of ACIX and its second implementation (ACIX II).

Following the recommendations of ACIX participants and Earth Observation data users, an additional inter-comparison of cloud masking assessment was decided to be performed in parallel with ACIX. Cloud masking is a crucial step of the radiometric pre-processing of optical remotely sensed data and an important contributor to the retrieval of accurate SR within an AC process. Therefore, it was considered essential to analyse these two processing chains together.

The test sites of the exercises are defined concerning representative land surface and atmospheric conditions, e.g. land/water, land cover, aerosols. Particular attention is given also to aquatic sites, i.e. coastal and inland waters, which are analysed as a separate category. All the exercises, i.e. CMIX, ACIX-Land, and ACIX-Aqua run in parallel and follow similar timeline. ACIX-Land timeline is presented below, follow the links to ACIX-Aqua and CMIX description and report.

For more information about ACIX-II - CMIX workshops, please follow the link to ESA earth online web pages. ACIX II - CMIX 1st WS, ACIX II - CMIX 2nd WS .