CHIME Selective Compression: baseline and mission extension

Copernicus Hyperspectral Imaging Mission for the Environment (CHIME) mission aims to enhance the Copernicus space component with precise spectroscopic measurements composed of 250 continuous narrow spectral bands (10 nm) in VNIR/SWIR spectral domain (400-2500 nm) sampled at 30 m over a swath of ~130 km. CHIME mission baseline is systematic acquisitions during the daylight part of the orbit, over all land surfaces including islands greater than 100 km2, coastal zones within 370 km distance from land. The amount of data to be transmitted to the ground is very large, making on-board data reduction mandatory. Considering the significant presence of clouds, a selective cloud compression has been designed and is currently under development. The principle is to detect clouds and then to compress with a lower data rate compared to the clear pixels. The compressor is based on the CCSDS 123.0-B-2 standard with evolution for selective compression as a function of the pixel class. The upcoming version of this standard (CCSDS 123.0-B-3) will integrate this selective compression feature, in part thanks to the work done for CHIME. The principle of this two-classes selective compression is presented together with the improvement of data reduction. The CHIME data reduction scheme is configurable for acquisitions along the orbit, leading to a flexible processing. It gives opportunity to extend applications. The paper presents an example of CHIME mission extension to detect “anomalies” over oceans that could be possible with on-board configurable selective compression