OPERATIONAL AIRBORNE THERMAL IMAGING SURVEYS

Abstract

This paper reviews the methodology and significant parameters which experience has shown to be required in the conduct of airborne infrared imaging surveys using optical‐mechanical line scanning systems in the three to five and eight to fourteen micron spectral regions. For nonrectilinearized infrared imagery to be compatible with uncontrolled mosaicking, all flight lines should be in the same direction, flight lines must be spaced to allow matching of only the central seventy degrees of each strip, and surveys must be flown parallel to the prevailing wind direction. High‐resolution detectors are recommended for most geological terranes, and high‐sensitivity detectors for imaging hydrological and certain geothermal terranes. Nighttime data collection has proven superior to daytime data collection for most applications and little difference is found between the interpretability of imagery resulting from longwave and that from shortwave infrared detectors. Automatic gain control (AGC) and attendant ac averaging effects are minimal over homogeneous terranes exhibiting low infrared emittance variations. Amplification circuitry using dc restoration and manual level and gain controls is necessary when imaging land/water contacts or terranes with large variations in infrared emittance. A signal differentiation capability proved useful in coal fire and thermal pollution surveys.