Modeling Radiation Pressure Accelerations: Earth Radiance Anisotropy, Spacecraft Shape and Global Sampling

In this study, we investigate the feasibility of a direct measurement of Earth's Energy Imbalance (EEI) from space via radiation pressure accelerations. EEI represents one of the most challenging Earth observations for climate change research and quantifies the fundamental rate of global heating in response to radiative forcings and feedbacks. Using state-of-the-art mission design and orbit determination software, we simulate Sun's and Earth's radiative pressure impact on spacecrafts of different shapes. We derive the Earth radiation (shortwave and longwave) intercepted by the spacecraft from observed radiative fluxes (Clouds and Earth's Radiant Energy System, CERES) and correct for radiance anisotropy using anisotropy factors derived from historical Earth Radiation Budget (ERB) missions. Anisotropy is a function of solar and satellite viewing geometry, as well as of scene type (surface and atmospheric properties) of each Earth element in view of the satellite at any point in time. In addition, we test the sensitivity of confounding forces, such as aerodynamic drag and Yarkovsky effects to spacecraft shape, and present preliminary results of a sampling study to quantify the bias of daily global mean net radiative flux associated with a sun-synchronous orbit crossing Earth's equator at 12 pm local time. Our investigations and software development will inform instrument and mission requirements relevant to the accurate measurement of EEI.