The Atmospheric Correction Intercomparison eXercise (ACIX), conducted within CEOS WGCV and coordinated by ESA and NASA, continues with its fourth phase ACIX‑IV Aqua. Within this framework, ACIX‑IV Aqua continues the established series of intercomparison activities addressing atmospheric correction over water bodies.

The exercise will start in the occasion of the 1st ACIX‑IV workshop at ESRIN (30 November – 1 December), where coordinators and participants will collaboratively define the experimental protocol and data selection, ensuring a harmonised and well‑documented implementation.

ACIX‑IV Aqua will combine simulated and real observations to support a comprehensive evaluation of atmospheric correction algorithms over water. The activities will focus on simulated CHIME Top-Of-Atmosphere observations produced by the DTE-S2GOS scene generator over inland and coastal waters under a variety of atmospheric conditions, alongside the use of hyperspectral datasets (e.g. EnMAP) collected over representative aquatic reference sites.

By comparing outputs from multiple processing approaches, the exercise aims to assess algorithm performance in optically complex environments, identify key strengths and shortcomings, and analyse common patterns and divergences between methods. The results will provide valuable insights for improving atmospheric correction over water surfaces and will contribute to advancing the consistency, reliability, and usability of aquatic EO products.

The ACIX-IV Aqua timeline is presented below with the main steps and goals of the projects.