The Honda Institute ofTechnology and the Phillips Laboratory have developed several advanced visible (0.4 -0.8 pnn)Irg Fourier Transform Spectrometer (IFTS) brassboards, which simultaneously acquire one spatial and one spectral dimension of the hyperspectral image cube. The initial versions of these instruments may be scanned across a scene or configured with a scan mirror to pick up the second spatial dimension of the image cube. The current visible hyperspectral imagers posses a combination offeatures, including (i) low to moderate spectral resolution for hundreds/thousands of spectral channels, (ii) robust design, with no moving parts, (hi) detector limited free spectral range, (iv) detector-limited spatial and spectral resolution, and (v) field widened operation.The utility ofthis type ofinstrument reaches its logical conclusion howev with an instmment designed to acquire all three dimensions ofthe hyperspectral image cube (both spatial and one spectral) simultaneously. In this paper we present the (i) detailed optical system designs for the brassboard instruments (ii) the orrem data acquisistion system, (üi) data reduction and analysis techniques unique to hyperspectral sensor systems which operate with photometric accuracy, and (iv) several methods to modify the basic instrument design to allow simultaneous acquistion ofthe entire hyperspectral image cube.The hyperspectral sensor systems which are being developed and whose utility is being pioneered by florida Tech and the Phillips Laboratory are applicable to numerous DoD and civil applications including (1) space object identification, (ii) radiometrically correct satellite image and spectral signature database observations (iii) simultaneous spatiaYspectral observations ofbooster plumes for stratigic and surrogate tactical misile signature identification, and (iv) spatial/spectral visible and infrared astronomical observations with photometric accuracy.

The Phillips Laboratory (PL) and the Florida Institute of Technology have developed several advanced visible (0.4 -0.8 jim) Imaging Fourier Transform Spectrometer (IFTS) brassboards. These instruments simultaneously acquire one spatial and one spectral dimension of the hyperspectral image cube, and may be scanned across a scene or configured with a scan mirror to pick up the second spatial dimension. Initial laboratory and field demonsti-ations bave indicated the utility hyperspectral imagery as a diagnostic technique for space object target spectral signature identification-a capability which is not presently available for routine use on any PL ground-based optical system. Our current visible hyperspectral imagers possess a combination of features, including (1) low to moderate spectral resolution for hundreds/thousands of spectral channels, (ii) robust design, with no moving parts, (iii) detector limited free spectral range, (iv) detector-limited spatial and spectral resolution, and (v) field widened operation. The IFTS design is also well suited for observations oftemporally varying scenes, in which simultaneous spatial/spectral signature information is required for a target which may be moving erratically within the field of view, or for other application where low to moderate spectral resolution yields useflul information. The HYSAT (ilyperspectral effite) brassboard has been used to observe sateffites and other space objects.In this paper we present (1) the optical system design and operational overview, (ii) laboratory evaluation spectra, and (iii) a sample ofthe first observational data taken with HYSAT.The hyperspectral sensor systems which are being developed and whose utility is being pioneered by the Phillips Laboratory are applicable to several important SOl (space object identification), military, and èivil applications including (i) spectral signature simulations, satellite model validation, and satellite database observations and (iii) simultaneous spatial/spectral observations ofbooster plumes for strategic and surrogate tactical missile signature identification. The sensor system is also applicable to a wide range of other applications, including astronomy, camouflage discrimination, smoke chemical analysis environmental/agricukural resource sensin& terrain analysis, and ground surveillance. Only SOl applications will be discussed here.

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The collection of spatial-spectral data of space objects is unique from most applications of spectral imaging technology. Space object identification requires collection of multiple frames of relatively low intensity, fast moving targets. The objective is to collect a single aggregate reflectance spectrum over the satellite and correlate this to orientation and solar phase angle. Higher statistical signal-to-noise can be achieved by averaging over the spatial dimension of a data frame. Blur was introduced by the tracking conditions in only the spatial dimension due to the design of the instrument. This blur allows some minimzation of camera noise that cannot be removed through conventional techniques.Spectral imaging is an emerging technology in the field of remote sensing. The acquisition of one dimension of spatial data and one dimension of spectral data simultaneously, while scanning a second spatial dimension, is being used for many downward or lateral looking purposes. The goal of the Phillips Laboratory/LIMI Spectral Imaging group is space object identification using this same technology. This mission is contrasted from the traditional remote sensing mission in that it is a low-light regime of transient, rapidly moving phenomenon requiring several frames over the course of the event (satellite pass). An average satellite pass is on the order of 3-4 visual magnitude with 5 minutes of useable duration for low earth orbits.Many things affect the apparent visual magnitude of a sateffite. Solar phase angle, orientation, size, distance, and intervening air mass affect the intensity of the received signal. While an order of magnitude guess can be made from cameras boresighted to the main telescope, a refmement of the exposure time must be made after taking the first exposure and examining the result.Several quality data frames are required to make any judgement on changes in spectrum with the small changes in orientation over the course of a pass. For satellites where the minor change causes negligible results, several frames can be averaged to provide a more statistically meaningful sample.The low-light level and the requirement for several frames per pass as well as the heretofore unknown nature of the sateffite spectra have led to the use of a Fourier Transform imaging spectrometer. The current device uses a Sagnac type shearing interferometer design for high throughput. O-8194-1833-1/95/$6.00 SPIE Vol. 2480 / 475 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/27/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

Building upon the work of Phillips, et al. (1990) and Eric Jakeman (1987), a simple experimental apparatus has been developed and consists of various lasers, a 60 cm beam expander/director designated T1, and a 1220 m target board outfitted with reflectors at the Malabar Test Facility, Phillips Lab OL-AG. Retroreflectors were used to ensure an exact path reversal through the intervening turbulence due solely to temperature differentials at the ground- air interface. This apparatus produces a doubly forward scattered coherent wave. Observation along the twice travelled beam path using a beam splitter and a simple refracting telescope, laser line filter, and video camera produced a basic gaussian profile with a 3db enhancement peak due to stong turbulence.