Description
The Conical Scanning Millimeter-wave Imaging Radiometer (CoSMIR) instrument is an airborne, 9-channel total power radiometer originally developed to calibrate and validate the Special Sensor Microwave/Imager/Sounder (SSMIS) for the Defense Meteorological Satellite Project (DMSP) F-series satellites. CoSMIR has four receivers near 50, 91, 150, and 183 GHz which measure horizontally polarized radiation with vertically polarized measurement capability at 89.0 and 165.5 GHz. CoSMIR was flown for calibration/validation of the SSMIS in 2004-2005 off coastal California. Currently, CoSMIR has been modified to play the role as an airborne high-frequency simulator for the GPM Microwave Imager (GMI). The 9 channels of CoSMIR for GMI validation are at the frequencies of 50.3, 52.6, 89 (H & V), 165.5 (H & V), 183.3±1, 183.3±3, and 183.3±7 GHz. All channels besides 89 and 165.5 GHz will be horizontally polarized.
CoSMIR performs both conical and cross-track scanning from left to right with conical scanning in the forward direction (aircraft direction of travel) only. The footprint size of CoSMIR measurement varies with aircraft altitude and instrument look direction. Receivers and radiometer electronics on the CoSMIR instrument are housed in a 21.5 cm diameter and 28 cm long cylindrical scan head, which is rotated by a two-axis gimbaled mechanism. There are two in-flight external calibration targets at cruising altitude: one heated to 328 K, and the other maintained at ambient temperature. Due to these onboard calibration targets, the data between 50 to 183 GHz have an accuracy of ±1 K. More information about the CoSMIR instrument can be found on the Mesoscale Atmospheric Processes webpage.
Measurements
CoSMIR measures microwave brightness temperatures at 9 microwave frequencies between 50 to 183 GHz. With two in-flight external calibration targets at cruising altitude (one heated to 328 K, and the other maintained at ambient temperature), the data have an accuracy of ±1 K.
Applications
- Satellite validation
- Precipitation, convection and cloud studies
- Tropical cyclone research
- Climate model improvement
| RANGE OF MICROWAVE FREQUENCIES | FOOTPRINT AT 11.8 KM AIRCRAFT ALTITUDE | SAMPLING FREQUENCY | IN-FLIGHT EXTERNAL CALIBRATION TARGETS | ACCURACY |
|---|---|---|---|---|
| 50 to 183 GHz | Conical scan: 1.3 km x 1.9 km Cross-track scan: 0.8 km x 0.8 km | Conical scan: 2 seconds Cross-track scan: 3 seconds | 328 K and ambient temperature | ±1 K |