Mine detection using instantaneous spectral imaging

The performance of a temporally and spatially nonscanning imaging spectrometer is examined in the context of mine detection. The instrument is described in terms of computed- tomography concepts, specifically the central-slice theorem. The critical system element is a sequence of three transmission sinusoidal-phase gratings rotated in 60 degree increments which achieve dispersion in multiple directions and into multiple orders. The dispersed images of the system's fieldstop are interpreted as 2D projections of a 3D object cube. Due to finite focal-plane array size, this computed-tomography imaging spectrometer (CTIS) is an example of a limited-view-angle tomographic system. The imaging spectrometer's point-spread- function is measured experimentally as a function of wavelength and position in the field-of- view. Reconstruction of the object cube is then achieved via the Maximum-Likelihood Expectation-Maximization algorithm under the assumption of a Poisson likelihood law. The CTIS was tested in five experiments, each experiment utilizing a different target scene displayed on a video monitor. The five target scenes were: a 'University of Arizona' target, two minefield scenes (based on field data) including a simulated mine-like object produced by a HeNe-laser beam-print, and two minefield scenes including a simulated mine-like object produced by a laser-diode beam-print. In all five cases, the CTIS yielded accurate spatial and spectral signatures of the mine-like targets.