Radiometer Calibration Using Colocated GPS Radio Occultation Measurements

Authors:
  • WBWilliam J. Blackwell
    William J. Blackwell
  • RBRebecca Bishop
    Rebecca Bishop
  • KCKerri Cahoy
    Kerri Cahoy
  • BCBrian Cohen
    Brian Cohen
  • CCClayton Crail
    Clayton Crail
  • LCLidia Cucurull
    Lidia Cucurull
  • PDPratik Dave
    Pratik Dave
  • MDMichael DiLiberto
    Michael DiLiberto
  • NENeal Erickson
    Neal Erickson
  • CFChad Fish
    Chad Fish
  • RLR. Vincent Leslie
    R. Vincent Leslie
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Abstract
We present a new high-fidelity method of calibrating a cross-track scanning microwave radiometer using Global Positioning System (GPS) radio occultation (GPSRO) measurements. The radiometer and GPSRO receiver periodically observe the same volume of atmosphere near the Earth's limb, and these overlapping measurements are used to calibrate the radiometer. Performance analyses show that absolute calibration accuracy better than 0.25 K is achievable for temperature sounding channels in the 50-60-GHz band for a total-power radiometer using a weakly coupled noise diode for frequent calibration and proximal GPSRO measurements for infrequent (approximately daily) calibration. The method requires GPSRO penetration depth only down to the stratosphere, thus permitting the use of a relatively small GPS antenna. Furthermore, only coarse spacecraft angular knowledge (approximately one degree rms) is required for the technique, as more precise angular knowledge can be retrieved directly from the combined radiometer and GPSRO data, assuming that the radiometer angular sampling is uniform. These features make the technique particularly well suited for implementation on a low-cost CubeSat hosting both radiometer and GPSRO receiver systems on the same spacecraft. We describe a validation platform for this calibration method, the Microwave Radiometer Technology Acceleration (MiRaTA) CubeSat, currently in development for the National Aeronautics and Space Administration (NASA) Earth Science Technology Office. MiRaTA will fly a multiband radiometer and the Compact TEC/Atmosphere GPS Sensor in 2015.
Funding Information
  • Assistant Secretary of Defense for Research and Engineering (FA8721-05-C-0002)

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