Comparisons between hyperspectral passive and multispectral active sensor measurements

We conducted experiments with side-by-side active and passive sensors in the 8-12 micron region in order to study similarities and differences in the spectral signatures detected by the two sensors. The active instrument was a frequency-agile CO2 lidar system operating on 44 wavelengths and at a total pulse repetition rate of 5 kHz. The passive system was an Aerospace Corp. dispersive imaging spectrometer with 128 spectral channels from 750-1250 cm-l. The sensors viewed both natural scenes and man-made objects typical of industrial scenes at ranges of 1-3 km along horizontal paths. Scenes were viewed under various ambient conditions in order to evaluate the effects of radiance contrast for the passive images at different times of a day. Both imaging and 'staring' experiments were conducted on the background scenes with a significant level of 'clutter'. Preliminary analysis shows that reflectance data (from an active sensor) does not necessarily have a simple relationship to passive data, which is influenced by ground emissivity, atmospheric radiance, and temperature differences.