Analysis of stellar radiance contamination in observed satellite spectra

ABSTRACT Reectance spectra of Earth orbiting satellites can be readily observed with small diameter telescopes ( D < 1m)by utilizing a method known as slitless spectroscopy. Satellite spectra can be observed by simply placing atransmission grating within the collimated optical path of the telescope without the need to image through aslit. The simplicity of the slitless spectroscopy design makes it a promising alternative to spatially resolvingsatellites with larger and more expensive diameter telescopes for applications of space situational awareness.However, accurately observing satellite reectance spectra without imaging through a slit requires a dark andhomogeneous background. This requirement is frequently violated as background stars streak across the imagedue to the slewing motion of the telescope during satellite tracking. Rather than throwing out all images withnoticeable stellar contamination, a principle component analysis of contaminated images from three geostationarysatellite observations showed that it may still be possible to assess and identify satellite characteristics dependingupon the amount of stellar contamination in the spectral region of interest. Additionally, a simple technique forautomatic removal of contaminated frames is proposed based on an outlier analysis using Gaussian statistics andwas found to successfully remove all signi cantly contaminated frames.Keywords: slitless spectroscopy, space situational awareness, satellite spectra, stellar contamination