Figure showing CoSMIR in laboratory calibration with liquid nitrogen. The four antenna apertures corresponding to the four receivers are visible.
CoSMIR is an airborne, 9-channel total power radiometer that was originally developed for the calibration/validation of the Special Sensor Microwave/Imager/ Sounder (SSMIS), a new-generation conical scanning radiometer for the DMSP (Defense Meteorological Satellite Project) F-series satellites. When first completed in 2003, the system has four receivers near 50, 91, 150 and 183 GHz, that measure horizontally polarized radiation at the frequencies of 50.3, 52.8, 53.6, 150, 183.3±1, 183.3±3, and 183.3±6.6 GHz, and dual polarized radiation at 91.665 GHz from on board the high-flying NASA ER-2 aircraft. All receivers and radiometer electronics are housed in a small cylindrical scan head (21.5 cm in diameter and 28 cm in length) that is rotated by a two-axis gimbaled mechanism capable of generating a wide variety of scan profiles. Two calibration targets, one maintained at ambient (cold) temperature and another heated to a hot temperature of about 328 K, are closely coupled to the scan head and rotate with it about the azimuth axis. Radiometric signals from each channel are sampled at 0.01 sec intervals. These signals and housekeeping data are fed to the main computer in an external electronics box.
CoSMIR has been flown only for calibration/validation of the SSMIS during years 2004-2005 off the coastal areas of California. Currently, it is being modified to play the role as an airborne high-frequency simulator for the GMI, which requires changes in both frequency and polarization for some channels. After modification, the 9 channels will be 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. The modified CoSMIR will fly in a GPM–related field campaign in Oklahoma during April-May 2011.
Key CoSMIR Facts
- Heritage: An improved version of GSFC airborne MIR (Millimeter-wave Imaging Radiometer), capable of acquiring radiometric data over the frequency range of 50-183 GHz in conical and/or across-track scan modes.
- On board the NASA ER-2 aircraft, performed calibration/validation of the high-frequency channels of the Special Sensor Microwave Imager/Sounder (SSMIS), a new generation orbiting microwave imager/sounder for the DMSP (Defense Meteorological Satellite Project) F-16 satellite, during 2004-2005.
- Modified to conform to high-frequency channels of the GMI (Global Precipitation Measurement mission Microwave Imager), and to acquire data in field campaigns for algorithm development of precipitation retrievals.
Nominal Field Configuration: CoSMIR is designed to operate on board the NASA ER-2 aircraft, but it can be installed and fly in other aircraft with an appropriate nadir port (e.g., DC-8 aircraft). As GMI (GPM Microwave Imager) airborne simulator, a new scan mode to acquire both conical and across-track scan data simultaneously in a given flight is implemented to satisfy the requirements of the PMM algorithm development team.
Frequencies: 9 channels at
- 89 (H & V)
- 165.5 (H & V)
- 183.3±7 GHz
Scan Modes: Programmable for conical scan at angles between 0 - 53.6°, across scan, or a combination of both.
In-flight Calibration: two external targets at ~ 328° K and at ambient temperature (~ 250° at ER-2 aircraft cruising altitudes)
Scan head: a cylinder 21.5 cm in diameter and 28.0 cm long
FOV: ~ 4° beam width (gives a nadir footprint at the surface of about 1.4 km at ER-2 cruising altitude of 20 km)
Gail Scofronick-Jackson, NASA Goddard Space Flight Center, Gail.S.Jackson@nasa.gov
Co-Investigators/ Team Members
- Bryan Monosmith / NASA Goddard
- James Wang / Science Systems and Applications, Inc.
CoSMIR Data Products
- Well-calibrated radiometric data between 50-183 GHz with accuracy on the order of ±1 K.
- Through various retrieval algorithms, the acquired data can be used to estimate snowfall rates, water vapor profiles (with known temperature profiles), light precipitation, and shallow snow cover on the ground.
J. R. Wang, P. E. Racette, J. E. Piepmeier, B. Monosmith, and W. Manning, “Airborne CoSMIR Observations Between 50 and 183 GHz over Snow-Covered Sierra Mountains,” IEEE Trans. Geosci. Remote Sens., 45(1), 55-61, 2007.
J. R. Wang, P. E. Racette, and J. R. Piepmeier, “A comparison of Near Concurrent Measurements from the SSMIS and CoSMIR for some Selected Channels over the Frequency Range of 50-183 GHz,” IEEE Trans. Geosci. Remote Sens., 46(4), 923-933, 2008.