Inner Belt Anisotropy Investigations Based on the Standard Radiation Environment Monitor (SREM)

The Standard Radiation Environment Monitor (SREM) is a particle detector developed for wide use on ESA spacecraft. It is flying on several ESA missions, most recently the Herschel and Planck space telescopes. Using data from the SREM unit on PROBA-1 in LEO, pitch angle anisotropics in the inner Van Allen belt are investigated. The sensitivity of the SREM to pitch angle induced flux anisotropics can be linked to the directional response function of the SREM, obtained using GRAS/Geant4 Monte-Carlo simulations. The directional response function is combined with an anisotropic version of the AP8 model (based on the Badhwar-Konradi anisotropy distribution) to yield improved count predictions. The importance of considering flux anisotropies is shown for both short-term data and long-term integrated counts. Significant improvements to the AP8 model can be realised.