The Cloud Masking Intercomparison eXercise (CMIX) is an international collaborative effort aimed at intercomparing cloud detection algorithms for spaceborne optical sensors with a moderate spatial resolution (10 – 30 m). CMIX is a joint activity by ESA and NASA in the frame of the CEOS working group on calibration and validation (WGCV) and focusses on open and free imagery.

Cloud cover has long been known to be a major limiting factor in exploiting time-series data acquired by optical spaceborne remote sensing sensors. While multiple methods have been developed to address the problem of cloud detection in satellite imagery and many cloud masks have been developed for optical sensors, very few studies have been carried out quantitative intercomparison of state-of-the-art methods in this domain. Based on this need, the first CMIX was started in 2018, leading to a final publication of the results in 2022 (Skakun et al. 2022). CMIX-II is the second iteration of the exercise, focused on open, free, and regularly acquired imagery acquired from Landsat 8 (NASA/USGS) and Sentinel-2 (ESA) missions.

CMIX II timeline.