Assessing the Quality of the Radiometric and Spectral Calibration of casi Data and Retrieval of Surface Reflectance Factors

The spectral and radiometric data quality of the Compact Airborne Spectrographic Imager (casi) was assessed using atmospheric modeling and fitting the band center location of the oxygen absorption feature centered around 0.762 pm. Atmospheric modeling was used to assess the quality of the radiometric calibration. A software program that locates the position of the oxygen absorption feature and performs atmospheric modeling was used to assess the spectml calibration of the scanner. These methods were adequate to reveal problems with the mdiometric and spectral calibmtion and spectral alignment. The analyses required image data with a continuous spectrum and were performed on spectral mode data. Based on one calibration target, two different methods for retrieving surface reflectance factors were applied to the spectral and spatial mode data, respectively Atmospheric modeling and normalization to the calibration target were used on the spectral image data because water vapor correction on a pixel-by-pixel basis was possible. Water vapor correction on a pixel-by-pixel basis was not possible on the spatial data, and surface reflectance retrieval was accomplished using modeled path radiance and field spectra from the calibration target. The quality of image data from a commercial scanner such as the Compact Airborne Spectrographic Imager (casi) may vary depending on the maintenance of the scanner. For every instrument the user must assess the quality of the calibration. The calibration data provided by the operator may not always be reliable; in the worst cases, small companies may go out of business and the remote sensing analyst is left with little additional post-flight information. Particularly in these cases it becomes important to be resourceful in assessing the quality of the radiometric and spectral calibration of the data.