INFRARED DETECTION OF LIQUIDS ON TERRESTRIAL SURFACES BY CO2-LASER HEATING

The strong mid-infrared bands of contaminant liquids wetting sand and soil can be remotely detected by 0 103-eV laser irradiation with beam intensity well below that which chars the terrain. Emissions from heated nonvolatile interstitial liquid layers and extinction of thermoluminescence by beam-generated vapors of volatile contaminants are spectrally distinct within the infrared contaminant fingerprint spectral region— as measured by a Michelson interferometer based FT-IR radiometer instrument. The contaminant’s vibrational resonance intensities change proportionally in magnitude and sign in measured contiguous difference FFT spectra, within a specific beam-to-sample dwell period. The onset irradiation time and period for detecting these bands can differ according to amount and volatility of contaminant, beam intensity and its time of dwell necessary to produce sufficient thermoluminescence flux, and on the quantity of interferogram data acquisitions. © 1990 Optical Society of America.