Compact Scanning Submillimter-wave Imaging Radiometer (CoSSIR)

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

  • HeritageAn instrument implemented for the measurements of ice clouds.  It has five receivers covering the frequency range of 183-874 GHz, that are housed in a compact cylinder 21.5 cm in diameter and 28.0 cm long.  All receivers at frequencies > 183 GHz were developed under the GSFC SBIR (Small Business Innovation Research) program.
  • Flown on the NASA ER-2 aircraft during CRYSTAL-FACE (Cirrus Regional Study of Tropical Anvils and Cirrus Layers – Florida Area Cirrus Experiment) in 2002, and TC-4 (Tropical Composition, Cloud and Climate Coupling) experiment in 2007. Data from TC4 can be obtained from CoSSIR Data Portal.
  • Recently modified to serve as an airborne simulator for the SIRICE (Submillimeter-wave and Infrared Ice Cloud Experiment), a potential NASA Earth science satellite mission, and to acquire data in field campaigns for algorithm development of ice cloud parameter retrievals.

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

  • Frequencies: 12 channels at
    • 183.3±1
    • 183.3±3
    • 183.3±7
    • 325±1.5
    • 325±3.5
    • 325±9.5
    • 448±1.4
    • 448±3
    • 448±7.2
    • 642 (H&V)
    • 874 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)

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

  • Well-calibrated radiometric data between 183-874 GHz with accuracy on the order of ±1 K.
  • Through various retrieval algorithms, the acquired data can be used to estimate ice cloud parameters (ice water path and mean ice particle size), snowfall rates, and water vapor profiles (with known temperature profiles).
    Data from TC4 can be obtained from CoSSIR Data Portal.


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.