Update on Low Earth Orbit Results from CIRiS, a Cubesat for Land Surface Temperature and Evapotranspiration Measurements from Space

CIRiS (Compact Infrared Radiometer in Space) is a CubeSat instrument for radiometric infrared imaging of land and water surfaces from space. Designed for future constellation missions with short revisit times, the instrument has a simple low-risk, low-volume architecture, combined with features for achieving high performance directed at land surface and other applications. Among the latter are evapotranspiration measurements, evaporative stress index, land and water body surface temperature mapping, and cloud radiation imaging. A development program has begun that combines CIRiS' multispectral radiometric function in the infrared with a similar capability at multiple visible wavelengths.

A major objective of the CIRiS mission is to achieve high radiometric accuracy, through selection of multiple parameter settings of the on-board calibration system. The entirely uncooled architecture also features on-board signal processing for SNR enhancement. CIRiS has been operating in Low Earth Orbit (LEO) since February of 2020. The CIRiS instrument images in three thermal infrared bands between 7.5 um and 13.5 um, including two bands for implementing the split window technique to correct for atmospheric absorption effects. Pushbroom scanning generates a continuous along track image, without gaps, in all three bands simultaneously. The on-board calibration system, with three calibration views, enables evaluation and optimization of various calibration schemes.

CIRiS is now in an orbit with 52 deg inclination and 460 km altitude. Pixel footprint on the ground is 160 m. Image sequences have been acquired with radiometric calibration applied before and after imaging sessions over various time periods. New images and characterization results, and ground testing of a follow-on instrument, will be discussed.