Current wide area pan-chromatic or dual band persistent surveillance systems often do not provide enough observable
data to maintain accurate and unique tracks of multiple objects over a large field of regard. Previous experiments have
shown augmentation with hyperspectral imagery can enhance tracking performance. However, hyperspectral imagers
have significantly slower coverage rates than persistent surveillance systems, essentially because a hyperspectral pixel
contains vector data while a standard image pixel is typically either scalar or RGB. This coverage rate gap is a
fundamental mismatch between the two systems and presents a technological hurdle to the practical use of hyperspectral
imagers for tracking multiple objects spread over the entire field of regard of persistent surveillance systems. In this
non-mapping hyperspectral application, we assume much of the information in a hyperspectral data cube is superfluous
background and need not be processed or even collected. The effective coverage rate of the hyperspectral imager can be
made compatible with modern persistent surveillance systems, at least for the objects of interest, by using a DMD to
judiciously select which data are collected and processed. A proof-of-concept sensor has been developed and
preliminary results are presented.
Small object detection with a low false alarm rate remains a challenge for automated hyperspectral detection algorithms
when the background environment is cluttered. In order to approach this problem we are developing a compact
hyperspectral sensor that can be fielded from a small unmanned airborne platform. This platform is capable of flying low
and slow, facilitating the collection of hyperspectral imagery that has a small ground-sample distance (GSD) and small
atmospheric distortion. Using high-resolution hyperspectral imagery we simulate various ranges between the sensor and
the objects of interest. This numerical study aids in analysis of the effects of stand-off distance on detection versus false
alarm rates when using standard hyperspectral detection algorithms. Preliminary experimental evidence supports our
simulation results.
A new approach for the design and fabrication of a miniaturized Hyperspectral imager is described. A unique and compact instrument has been developed by taking advantage of light propagation within bonded solid blocks of fused silica. The resulting microHSI is a VNIR hyperspectral sensor capable of operating in the 400-1000 nm wavelength range developed, patented, and built by NovaSol. The microHSI spectrograph weighs 12.4 oz from slit input to camera output. The microHSI can accommodate either custom foreoptics or C-mount input lenses to adapt to a wide range of fields-of-view (FOV). The prototype microHSI uses a telecentric F2.8 foreoptic, with 36 mm focal length, to cover a 15 degree FOV. It can resolve 960 spatial pixels, resulting in a 280 μrad IFOV for this particular foreoptics implementation. With a 1 nm/unbinned pixel dispersion, the spectrometer spectral resolution is 3.5 nm. Results of field and laboratory testing of the prototype microHSI are presented and show that the sensor consistently meets technical performance predictions. The prototype microHSI employs a holographic diffraction grating embedded within the optical blocks resulting in a 19% diffraction efficiency. Future units are anticipated to incorporate a blazed grating for improved throughput and SNR. The microHSI concept can be extended to operation over other wavelength regions. Designs are nearing completion for a SWIR version of the device, and a miniaturized LWIR microHSI sensor is currently at the conceptual design stage.
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