Figure showing CoSSIR in system functional check.  The five antenna apertures corresponding to the five receivers are clearly displayed.

The Compact Scanning Submillimeter-wave Imaging Radiometer (CoSSIR) is an airborne, 12-channel, (183 - 874 GHz) total power imaging radiometer that was mainly developed for the measurements of ice clouds.  But it can be used for estimation of water vapor profiles and snowfall rates. When first completed and flown in the CRYSTAL-FACE field campaign during July 2002, the system had 15 channels at different frequencies from those listed below.  All the 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.

Key CoSSIR Facts

Nominal Field Configuration: CoSSIR is designed to operate on board the NASA ER-2 aircraft, but it has also been installed in WB-57 aircraft.  In both CRYSTAL – FACE and TC-4, the system acquired data mainly in conical scan mode.  Recently, a new scan mode to acquire both conical and across-track scan data simultaneously during a given flight was successfully implemented and tested to satisfy the future science requirements.

CoSSIR Parameters

Compact Scanning Submillimter-wave Imaging Radiometer (CoSSIR) Opening a New Window on Studies of Ice Cloud Properties

Ice cloud measurements (WB-57 aircraft) near Costa Rica on January 27, 2006 (WB-57 aircraft).  The main features are:

  1. Profiles of  ice clouds measured by the GSFC Cloud Radar System (WB-57). 
  2. CoSSIR sensitivity to ice clouds at several selected frequencies.  The 640 GHz channel shows a high sensitivity to thin cirrus on the far right.  The difference between the two 183.3 GHz channels is caused by water vapor absorption.
  3. Retrieved ice water path (IWP) and mass-weighted particle diameter (Dme) from the CoSSIR measurements.  The retrievals cover more than four order of magnitudes in IWP and 100-600 µm in Dme.  
  4. Retrieved polarization index (PI).  This represents the very first measurement of its kind.  PI is near zero in the clear regions and in the deep convective cores, but has values ranging from 0.1 to 0.3 in the anvils.  This suggests that particles in the anvils have high aspect ratio  while those in convective cores are  more spherical (e.g., graupel).  

Principal Investigator

Frank Evans, University of Colorado, Boulder, Colorado

Further information about CoSSIR and submm remote sensing may be found at:


David Starr, NASA Goddard Space Flight Center, Greenbelt, MD.

Team Members

Bryan Monosmith / NASA Goddard

CoSSIR Data Products


K. F. Evans, J. R. Wang, P. E. Racette, G. Heymsfield L. Li,  “Ice Cloud Retrievals and Analysis with Data from the Conical Scanning Submillimeter Imaging Radiometer and the Cloud Radar System during CRYSTAL-FACE,” J. Appl. Meteor., 44, 839-859, June 2005.
J. R. Wang, L. A. Chang, B. Monosmith, and Z. Zhang, “Water Vapor Profiling From CoSSIR Radiometric Measurements, IEEE Trans. Geosci. Remote Sensing, 46(1), 137-145, 2008.