A standoff method of detecting liquids on terrestrial and synthetic landscapes is presented. The interstitial liquid layers are identified through their unique molecular vibration modes in the 7.14–14.29-μm middle infrared (fingerprint) region of liberated thermal luminescence. Several seconds of 2.45-GHz beam exposure at 1.5 W cm<sup>−1</sup> is sufficient for detecting polydimethyl siloxane lightly wetting the soil through its fundamental Si–CH<sub>3</sub> and Si–O–Si stretching modes in the fingerprint region. A detection window of thermal opportunity opens as the surface attains maximum thermal gradient following irradiation by the microwave beam. The contaminant is revealed inside this window by means of a simple difference-spectrum measurement. Our goal is to reduce the time needed for optimum detection of the contaminant’s thermal spectrum to a subsecond exposure from a limited intensity beam.
© 1999 Optical Society of America
(040.3060) Detectors : Infrared
(070.4790) Fourier optics and signal processing : Spectrum analysis
(070.5010) Fourier optics and signal processing : Pattern recognition
(120.0280) Instrumentation, measurement, and metrology : Remote sensing and sensors
(300.6300) Spectroscopy : Spectroscopy, Fourier transforms
Arthur H. Carrieri, Irving F. Barditch, David J. Owens, Erik S. Roese, Pascal I. Lim, and Michael V. Talbard, "Thermal Luminescence Sensor for Ground-Path Contamination Detection," Appl. Opt. 38, 5880-5886 (1999)