Mid-Infrared Remote Sensing Systems and Their Application to Lithologic Mapping

Mid-infrared remote lithologic mapping by emittance and by reflectance are assessed in laboratory experiments. The emittance spectra of various rocks and minerals, measured in the 8-13,μ m atmospheric transmission window, are compared with reflectance data measured in the range of 9.2-11.2 μm using a line-tuned CO2laser. We conclude that the reflectance data are more useful for lithologic discrimination than the passive emittance data. An experimental laser suitable for terrain mapping from a low-flying aircraft is described. The low-pressure longitudinal discharge CO2laser has a rotating mirror to scan the diffraction grating and generates 90 bursts of pulses per second. Each 1-ms burst contains 92 pulses at 92 CO2laser wavelengths. The mean output power is 12 W and the average pulse power is 370 W. With that power, and using incoherent detection, a signal-to-noise ratio of better than 100: 1 should be obtained from terrain with an albedo of 0.01 at a height of 500 m.