Mapping surface mineralogy and scattering behavior using backscattered reflectance from a hyperspectral midinfrared airborne CO2 laser system (MIRACO(2)LAS)

Airborne, high-spectral resolution, thermal-infrared (TIR) MIRACO(2)LAS ref lectance data mere evaluated for mapping surface mineralogy and scattering behavior for a variety of semi-arid, geological test sites in Australia. MI RACO(2)LAS is a rapidly tuned, airborne CO2 laser system that measures back scattered (bidirectional) reflectance at 100 wavelengths between 9.1 and 11 .2 mu m for 2-m footprints in line profile mode. An operational methodology is described that permits reduction of the raw airborne signal-to-ground r eflectance. This ground reflectance has two major properties, namely, wavel ength-dependent mineralogical variations and reflection albedo variations r elated to surface roughness. Comparisons between the airborne MIRACO(2)LAS spectra and laboratory directional hemispherical reflectance (DHR) spectra show the same spectral shapes, though differences in average reflectance (a lbedo) occur for some types of rocks, The minerals identified using MIRACO( 2)LAS include silicates (for example, quartz, microcline? plagioclase, alma ndine, spessartine, talc, tremolite, and kaolinite) and carbonates (dolomit e and magnesite) as well as vegetation (dry and green). Many of the diagnos tic spectral features that allow identification of these materials are narr ow (<0.2 mu m), making them difficult to detect with broadband TIR systems, like the airborne TIMS and satelliteborne ASTER. Based on an empirical rel ationship between the minimum and maximum reflectance established using lab oratory DHR spectra, a method is proposed that allows the use of MIRACO(2)L AS data to identify surfaces that are characterized by Lambertian or specul ar scattering. The MIRACO(2)LAS results show that Lambertian-type scatterer s include soils and many types of isotropic rocks (no aligned flat surfaces or mineral foliation), Specular-type scatterers include water and anisotro pic rocks. This ability to map a given pixel's scattering behavior has impl ications for temperature-emissivity separation (TES) in passive TIR data, a s MIRACO(2)LAS can be used to provide an independent estimate of emissivity , provided the surface is judged to be a Lambertian scatterer.