Calibration of the compact mid-wave imaging system (CMIS), a candidate for low-cost, low SWaP instrument for weather satellites

We report on the calibration of the Compact Midwave Imaging Sensor (CMIS) which has been developed by The Johns Hopkins University - Applied Physics Lab (JHU/APL) under a grant from the NASA Earth Science Technology Office (ESTO). At the heart of the CMIS instrument is a newly-developed high operating temperature (HOT) detector made from III-V compounds in a Type II Superlattice design. The instrument is sensitive to 3 particular bands in the IR spectrum which have been noted for their usefulness in determining cloud coverage and temperatures. The bands used were centered at 2.25 μm, 3.75 μm and 4.05 μm. The focal plane array (FPA) was based on the FLIR ISC0405 640×512 pixel readout integrated circuit with 15 μm square pixels. The CMIS design included a 5 zone "butcher block" filter placed in close proximity to the FPA and refractive optical elements contained inside the barrel of the cold shield such that the optics were cooled to approximately the same temperature as the FPA. A small-size, low-power closed-cycle cooler was used to maintain the FPA and the optics at a temperature of 150 K, at which the dark current was low enough to allow integration times longer than 50 ms for cold background scenes. JHU/APL developed the camera control electronics (CCE) and data processing unit (DPU) for running the FPA, performing image processing functions on the data and storing it in memory. The CCE and DPU were designed for possible use on an orbital payload but for the airborne flight the commercial versions of some of the parts specified for spaceflight were used. This paper will describe the laboratory calibration procedures and results.