Highly Physical Penumbra Solar Radiation Pressure Modeling for GRACE and GOCE

Wednesday, 17 December 2014
Robert V Robertson, Virginia Polytechnic Institute and State University, Blacksburg, VA, United States and Jakob Flury, Leibniz University of Hannover, Hannover, Germany
The primary objectives of the GRACE (Gravity Recovery and Climate Experiment) and GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) missions are to characterize the mean and time variable components of Earth’s gravity field. The two GRACE satellites and the GOCE satellite provide high accuracy accelerometer data which is useful for a variety of other applications including thermosphere density and wind modeling and the study of variations in Earth’s neutral density. Solar radiation pressure (SRP) modeling is important to these applications. During penumbra transitions, SRP is influenced by the passage of solar radiation through Earth’s lower atmosphere. We have developed a highly physical SRP model to improve the accuracy of SRP force modeling during penumbra transitions. This high fidelity model is called: SRP with Oblateness and Lower Atmospheric Absorption, Refraction, and Scattering, or SOLAARS. SOLAARS uses a finite element approach which models the solar radiation field at each spacecraft location using a finite number of light rays. The spectral composition, angle of incidence, and solar flux associated with each light ray is computed based on physical modeling of atmospheric refraction and wavelength dependent extinction (absorption and scattering) processes. We will present new GRACE and GOCE penumbra SRP modeling results and investigate the influence of recently added modeling of atmospheric extinction processes. Additionally, we will illustrate the influence of atmospheric conditions on penumbra SRP and how selection of these variables can affect agreement of SOLAARS results with accelerometer data.