CHRIS is a small imaging spectrometer (14 kg with electronics), operating over the spectral range from 415nm to 1050nm, using a silicon-CCD detector. It has spectral resolution varying from 1.25nm to 11nm (better in the blue region). It has ground sample distance of 17m and a swath width of 13km. It includes a relatively conventional two-mirror telescope forming a scene image on the spectrometer entrance slit. The spectrometer design is based around use of curved prisms within a concentric 3-mirror relay (modified Offner). This design form, unique originally but since copied in other hyperspectral developments, has special advantages in wide spectral range, and in control of stray light.
CHRIS was designed by Dan Lobb and built by Sira for a free ride on the 1st ESA PROBA platform, launched in 2001. Originally intended just to provide data for only one year, to exercise the experimental platform, it is still working after more than 15 years in orbit. Over much of this period, it has been the only instrument in orbit with comparable performance, and it has built-up a clientele of over 50 scientific user groups.