CoSMIR is nine channel total power radiometer, spanning 50 GHz to 183 GHz, originally designed for calibration and validation of the Special Sensor Microwave Imager/Sounder. Since its construction, it has been modified to conform to the GPM Microwave Imager (GMI) high frequency channels. CoSMIR has flown on NASA’s ER-2 and DC-8 aircraft. The two-axis gimbaled scan mechanism allows for a variety of scan strategies, including conical and across-track scans.