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Two calibration/validation efforts planned for current and future spaceborne microwave sounding instruments
will be presented. First, the NPOESS Aircraft Sounder Testbed-Microwave (NAST-M) airborne sensor is used
to directly validate the microwave radiometers (AMSU and MHS) on several operational satellites. Comparison
results for underflights of the Aqua, NOAA, and MetOp-A satellites will be shown. Second, a potential approach
will be presented for on-orbit field-of-view (FOV) calibration of the Advanced Technology Microwave Sounder
(ATMS). A variety of proposed spacecraft maneuvers that could facilitate the characterization of the radiometric
boresight of all 22 ATMS channels will be discussed.
Radiance observations from the NAST-M airborne sensor can be used to directly validate the radiometric
performance of spaceborne sensors. NAST-M includes a total of four spectrometers, with three operating near the
oxygen lines at 50-57, 118.75, and 424.76 GHz, and a fourth spectrometer centered on the water vapor absorption
line at 183.31 GHz. All four feedhorns are co-located, have 3-dB (full-width at half-maximum) beamwidths of
7.5° (translating to 2.5-km nominal pixel diameter at nadir incidence), and are directed at a single mirror
that scans cross-track beneath the aircraft with a nominal swath width of 100 km. We will present results
for two recent validation efforts: 1) the Pacific THORpex (THe Observing-system Research and predictability
experiment) Observing System Test (PTOST 2003, Honolulu, HI) and 2) the Joint Airborne IASI Validation
Experiment (JAIVEx 2007, Houston, TX). Radiance differences between the NAST-M sensor and the Advanced
Microwave Sounding Unit (AMSU) and the Microwave Humidity Sensor (MHS) were found to be less than 1K
for most channels. Comparison results for ocean underflights of the Aqua, NOAA, and MetOp-A satellites are
shown.
We also present an approach for on-orbit FOV calibration of the ATMS satellite instrument using vicarious
calibration sources with high spatial frequency content (the Earths limb, for example). The antenna beam is
slowly swept across the target of interest and a constrained deconvolution approach is used to recover antenna
pattern anomalies. Various proposed spacecraft maneuvers will be considered, with the intent to illustrate how
each maneuver will help to identify and characterize possible FOV artifacts. Radiative transfer simulations that
quantitatively assess the benefit of each satellite maneuver will also be presented.
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