(ATBD) SMAP Level 1 Radar Data Products - NASA

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12.2.2 Radiometric Accuracy Validation
Radiometric accuracy validation can be divided into the reduction of short-term
variability coming from the instrument, and vicarious calibration against external
reference targets. Short term variations of transmit power and receiver gain are
expected due primarily to temperature variations. Pre-launch models based on the
loopback data will be constructed and implemented in the calibration preprocessor
to supply the L1B and L1C processors with time varying calibration coefficients.
During the L1 cal/val period, the performance of the loopback calibration modelling
will be validated by plotting the loopback measurements and the output σ 0 results
with and without the loopback correction against time and temperature.
Vicarious calibration will be handled by collecting and averaging data in the
L1B and L1C processors over stable calibration target areas such as the Amazon,
the oceans, and the ice sheets. Assuming that these data are stable, they can be
used to track longer term trends in system performance, and to catch other issues
such as biases between polarization channels, antenna pointing knowledge errors,
RFI, and Faraday rotation effects. Comparisons with Aquarius and PALSAR-2 data
(if available) and other instruments will be useful to separate instrument variations
from possible scene variations.
12.2.3 Geolocation Validation
Final verification of geolocation will be performed post-launch by looking at highcontrast
features with known locations. Coastlines and shorelines should work well
and are widely available. Some natural or man-made point-like targets may also
work. Specific candidate targets should be identified prior to launch. It may be
beneficial to conduct this validation with the high resolution single look image data.
13 Acknowledgments
This work was performed at the Jet Propulsion Laboratory, California Institute of
Technology, under contract with the National Aeronautics and Space Administration.