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Aiming to analyze the influence of earth-atmosphere radiation on imaging characteristics of space object. A scene of space object motion and detection was designed by Satellite Tool Kit (STK) where visible light imagers mounted on geosynchronous earth orbit (GEO)/medium earth orbit (MEO) satellites were treated as observation platform, highly elliptical orbit (HEO) satellite was treated as object. Equivalent magnitude models of space object and earth-atmosphere radiation, and formulation for signal-to-noise ratio (SNR) of space object were derived by adopting infinitesimal method, according to spatial relationship between space object, earth, sun, and observation platform. The variation of equivalent magnitude between object and earth-atmosphere radiation, as well as the SNR were analyzed when tracking detector and gazing detector were arranged on observation platform. Simulation results indicate that the SNR of object on low orbit observation platform is higher than that on high orbit observation platform, the SNR of the former is 1.1 orders of magnitude higher than the latter on average, while the average imaging SNR of the latter is 1.9. Tracking detector’s object SNR is higher than gazing detector, the difference is largest when object enters or leaves detecting field of view, yet it is the smallest when object is close to detecting field of view. Moreover, the value of SNR obtained by simulation provides a guidance for the detection and recognition of space object, as well as a way of reduction of earth-atmosphere radiation.
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