A Robust Accurate Earthshine Skyshine Reflection Model for Remote Space Objects

The Air Force space situational awareness mission includes the characterization, identification and real-time tracking of man-made resident space objects (RSO).  Classification and tracking is affected not only by background contrast but also by the reflected environment irradiance that contributes to its signature.  The total irradiance on the object from Earthshine/Skyshine and Airglow emissions is important for predicting signature during dawn, dusk and night time.  RSO materials have strongly directional reflectance properties and strong spectral variations.  The earthshine/skyshine sources are difficult to model accurately and have not received adequate attention in existing signature models.  Spectral Sciences, Inc. (SSI) proposes in SBIR Phase I to provide a first principles detailed toolkit named Robust and Accurate Earthshine/Skyshine Reflection Models, (RAES-RM) for accurate determination of earthshine and skyshine radiance in the ultraviolet, visible and infrared spectral regions, and to accurately model the reflection of the various sources using the full bi-directional reflectance distributions of the RSO materials.  To develop this model we will leverage current first-principles models developed under current and previous SSI SBIRs.  We will build on SSIs extensive experience in atmospheric radiance models, and team with Surface Optics Corporation to incorporate their material BRDF measurements. BENEFIT: The anticipated results of the proposed work will be the accurate modeling capability that will encompass the UV/Visible/IR spectral regions. The model will accurately determine effects of earthshine/skyshine and airglow contributions to target signatures, and accurately compute the target radiance from the reflected illuminations using a complete BRDF description. The Phase I work builds the architecture, and tests the accuracy and robustness of the RAES-RM model with full development in Phase II, when RAES-RM will be interfaced with target codes such as TASAT, FLITES and OSC, and tested in realistic scenarios. The product of the proposed SBIR project, after Phase II, will be a new ensemble of software modules that simulate the radiant effects of earthshine and skyshine on illumination of space objects. RAES-RM will provide Government and commercial satellite designers and operators a unique tool for predicting the visibility of their systems, or threat systems, under any geometry, given global environment conditions.