The Conical Scanning Millimeter-wave Imaging Radiometer (CoSMIR) is an airborne hyperspectral radiometer with frequencies between 50 and 191 GHz. CoSMIR was originally developed for the calibration/validation of the Special Sensor Microwave Imager/Sounder (SSMIS). When first completed in 2003, the system had four receivers that measured horizontally polarized radiation at 50.3, 52.8, 53.6, 150, 183.3±1, 183.3±3, and 183.3±6.6 GHz, and dual-polarized (vertical and horizontal) radiation at 91.665 GHz. Following the SSMIS cal/val efforts, CoSMIR served as the airborne high-frequency simulator for the Global Precipitation Measurement (GPM) Microwave Imager (GMI) in four GPM field campaigns from 2011 to 2015. The channels were modified slightly to match the GMI channels more closely: 53.6 was removed, 91.655 changed to 89.0, 150 changed to 165.5 and made dual-polarized, and 183.3±6.6 changed to 183.3±7. In 2020 and 2022, CoSMIR flew on the NASA ER-2 in IMPACTS (Investigation of Microphysics and Precipitation for Atlantic Coast Threatening Snowstorms). CoSMIR’s submillimeter-wave sibling (CoSSIR) flew in the third deployment of IMPACTS in 2023.

CoSMIR was modified in 2023 through Decadal Survey Incubation (DSI) funds to become CoSMIR-Hyperspectral (CoSMIR-H). The instrument retained the 89 and 165 GHz dual-polarized channels and switched out the 50 and 183 GHz receivers for hyperspectral receivers spanning 50-58 GHz and 175-191 GHz, providing thousands of channels at these frequencies instead of the previous two 50-GHz and three 183-GHz channels. Engineering check flights of CoSMIR-H on the ER-2 were successfully completed in July 2024 and CoSMIR-H will fly again as the primary instrument in the WHyMSIE campaign in Oct/Nov 2024.

All the CoSMIR 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 323 K, are closely coupled to the scan head and rotate with it about the azimuth axis. Radiometric signals from each channel are sampled at 10 ms intervals. These signals and housekeeping data are fed to the main computer in an external electronics box.

CoSMIR Parameters

• Frequencies:

  o 2048 channels at 50-58 GHz, 4 MHz spectral resolution, horizontal polarization

  o 4096 channels at 175.31-191.31 GHz, 4 MHz spectral resolution, vertical polarization

  o 4 channels at 89.0 and 165.3, vertical and horizontal polarization

  o Hyperspectral channels can be averaged in ground processing to create desired bandwidths and center frequencies

• Scan modes: Programmable for conical scan at angles between 0-53°, cross/along-track scan, or a combination of both

• In-flight Calibration: two external targets at ~323 K and at ambient temperature (typically 230-250 K, depending on aircraft cruising altitude)

• Scan head: a cylinder 21.5 cm in diameter and 28.0 cm long

• Field of view: ~4° beam width – gives a footprint at the surface of 1.4 km at nadir and 2.3x3.9 km at 53° off-nadir at ER-2 cruising altitude of 20 km

• Aircraft: Flown previously on the NASA DC-8 and ER-2.

Data Products

• Level 1 quality-controlled, geolocated, calibrated brightness temperatures between 50 and 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, temperature profiles, light precipitation, and shallow snow cover on the ground.

• CoSMIR Level 1 data from the GPM field campaigns and IMPACTS are available on the GHRC DAAC

        http://dx.doi.org/10.5067/GPMGV/MC3E/COSMIR/DATA101 

        http://dx.doi.org/10.5067/GPMGV/GCPEX/COSMIR/DATA101 

        http://dx.doi.org/10.5067/GPMGV/IPHEX/COSMIR/DATA101 

        http://dx.doi.org/10.5067/GPMGV/OLYMPEX/COSMIR/DATA101 

        http://dx.doi.org/10.5067/IMPACTS/COSMIR/DATA101 

Team Members

Principal Investigator

Rachael Kroodsma

NASA Goddard Space Flight Center, Code 612

rachael.a.kroodsma@nasa.gov 

Lead Engineer

Matt Fritts

NASA Goddard Space Flight Center, Code 555

matthew.a.fritts@nasa.gov

References  

Kroodsma, R. A., M. A. Fritts, J. F. Lucey, M. R. Schwaller, T. J. Ames, C. M. Cooke, and L. M. Hilliard, 2019: CoSMIR performance during the GPM OLYMPEX campaign, IEEE Trans. Geosci. Remote Sens., 57(9), 6397-6407.

Wang, J. R., G. M. Skofronick-Jackson, M. R. Schwaller, C. M. Johnson, W. B. Monosmith, and Z. Zhang, 2013: Observations of storm signatures by the recently modified conical scanning millimeter-wave imaging radiometer, IEEE Trans. Geosci. Remote Sens., 51, 411-424.

Wang, J. R., P. E. Racette, and J. E. Piepmeier, 2008: 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, 923-933.