Solar radiation based
calibration of an airborne radiometer for vicarious calibration of earth
observing sensors
Remote Sensing Group, University of
Arizona
Airborne
radiometric instruments are often used to measure upwelling radiance, whether
for producing remote sensing imagery, for performing vicarious calibration of
satellite sensors, or for correcting atmospheric effects. The Remote Sensing Group (RSG) at the
University of Arizona relies on airborne measurements for its radiance-based,
vicarious calibration approach. In this approach the radiometer is flown over a
selected test site at the time of a sensor overpass to predict the radiance at
the sensor to be calibrated. The
advantage of an airborne approach is that it allows measurements to be made
above the absorbing and scattering properties of the atmosphere. Since the prediction of the radiance at the
sensor to be calibrated depends heavily on the calibration of the airborne
sensor, the success of the radiance-based method depends critically on the
calibration of the radiometer.
Typically these airborne radiometers are calibrated in a laboratory environment with incandescent radiance sources whose spectral outputs are known relative to some established standard. In the field, the radiometers are operated in an environment with a source that has a different spectral output, namely the sun. To avoid the problem of the differences between the spectral nature of the lamp-based calibration sources and the sun, the solar radiation based calibration (SRBC) was developed. The major advantage of this method is that the source for the calibration is the same source used in acquiring field measurements. An important concern is determining the extent by which calibration coefficients generated using laboratory based techniques differ from those produced by solar based methods. SRBC results for an Exotech model 100BX radiometer are compared to laboratory radiometric calibrations based on a spherical integrating source (SIS) and a lamp source in the RSG’s blacklab and the details of all three methods of calibration will be discussed.