Solar radiation based calibration of an airborne radiometer for vicarious calibration of earth observing sensors

Airborne radiometric instruments are often used to collect radiance data, whether for producing remote sensing imagery, for use in vicarious calibration, or for atmospheric correction. Reflected radiance from a test site is detected by an Exotech model 100BX radiometer that contains four different spectral filters which coincide with the first four bands of Landsat Thematic Mapper (TM). These filters can be interchanged with filters that correspond to the first three multispectral bands of SPOT. Typically these radiometers are calibrated in a laboratory environment with incandescent radiance sources whose spectral outputs are known by some established standard. In the field, the radiometers are used with a different source than that used for the laboratory calibration, namely the sun. The solar radiation based calibration (SRBC) has been demonstrated to be an accurate calibration method for these instruments. The major advantage of this method is that the source for the calibration is the same source used in acquiring field measurements. In this work, solar radiation based calibration is compared to laboratory radiometric calibration done with a spherical integrating source (SIS) and a lamp source in the Remote Sensing Group (RSG) blacklab for airborne radiometers. Results of measurements taken over Ivanpah Playa on 6 July 2000 and 4 June 2000 by an Exotech model 100BX calibrated with these methods are presented and biases in the three different calibration methods are discussed.