The potential role of thermal infrared multispectral scanners in geological remote sensing

Thermal infrared scanners with multiple channels in the 8-14-µm wavelength region are important for geological remote sensing because this spectral region contains important compositional information about silicate rocks and minerals that cannot be duplicated by remote sensors operating elsewhere in the electromagnetic spectrum. Emittance minima in this spectral region, caused by interatomic oscillations, occur at different wavelengths depending on silicate rock type. It has been demonstrated that an image constructed from a signal that is proportional to a ratio of radiances in two thermal scanner channels can be used to map compositional (chemical and mineral) variations in silicates, while suppressing temperature variations across a scanned scene. Theoretical studies indicate that future infrared scanners with eight to twelve channels in the 8-14-µm region might be used to produce an image that could be simply level-sliced (divided into discrete gray levels) to map silicate rocks according to traditional rock classification charts. This is a field in which sensor technology is still the limiting factor. However, improvements in extrinsic sensor properties, especially an increase in the number of spatially coregistered detector elements in a single dewar, are more important than improvements in intrinsic properties, such as detectivity.