Investigation of disturbed earth detection in the very long wavelength infrared (VLWIR)

Abstract

Undisturbed soil generally consists of larger silica particles where the smaller particles have been removed from the surface by weathering, i.e., rain. Large silica particles exhibit a significant reflectance in the 7 – 12 μm spectral region called the Reststrahlen band. It has been demonstrated that the Reststrahlen band intensity is proportional to the particle size distribution of silica in the soil; as the proportion of small to large silica particles increases the Reststrahlen band also decreases in intensity. When soil is disturbed, for example when an object is buried, the distribution of silica particles is changed such that the “new” surface consists of a greater proportion of small to large silica particles. The increased number of small silica particles decreases the intensity of the Reststrahlen band therefore enabling detection of buried objects by imaging in the 7 – 12 μm spectral range. There is a second reflectance band in the 17 – 25 μm spectral region which has not been used for detection of buried objects. We investigate the behavior of this second Reststrahlen band for disturbed earth and evaluate its use for enhanced detection of buried objects when combined with the first Reststrahlen band.