Fourier filtering of hyperspectral imagery of space objects to reduce camera noise

Abstract

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