Terrestrial Imaging in the Thermal Infrared Using a Quantum Well Detector Array

Abstract

There are many practical applications of thermal imaging in atmospheric windows where there is little absorption by molecular water; these windows are from 3 to 5 microns and from 8 to 12 microns 111. In the past the 3 to 5 micron waveband has been heavily utilized for thermal imagery, however, sensitivity of thermal imagers and radiometers can be improved by working in the 8 to 12 micron band. We have built an imaging radiometer (8 to 12 microns) using a square-format array of state-of-the-art aluminum gallium arsenide (AlGaAs) quantum well detectors. The array performance was evaluated in terms of D*, quantum efficiency and uniformity; then the field-performance of the radiometer was evaluated by flying over varied terrain near Chincoteague, Virginia and obtaining images with resolution of about 1 square meter per pixel. We obtained excellent images even without correcting for pixel response variations. The optimum operating temperature of this array was determined to be approximately 50 K. Although this is too low for many space applications, future improvements in the detectors should significantly raise the operating temperature. At present this type of radiometer is a viable candidate for aircraft experiments.