Multi-satellite SEP observations by the GPS energetic particle detector constellation

Los Alamos National Laboratory has been flying energetic particle detectors on the GPS spacecraft for the last two solar cycles. The latest generation of instruments - CXD (Combined X-ray Dosimeters) are currently deployed on 7 GPS spacecraft providing unprecedented temporal and spatial coverage in the outer radiation belts above L=4 (invariant latitude ~60 degrees), for proton energies from 6 to >75 MeV. Access of SEP to the inner magnetosphere is a function of both energy, altitude and geomagnetic activity. Typical vertical cutoff rigidity at L=4 is around 1 GV (momentum per unit charge) or ~ 400MeV for protons. However, Thus the GPS constellation is well suited to observing the geomagnetic cutoff process "in action" for energies from ~ 6 to ~ 100 MeV and to investigate the detailed MLT, L and activity dependence of the SEP spectra. We will present here details of the SEP data available from the CXD instruments together with the spectral inversion techniques used to recover detailed spectra from the wide energy response dosimeter channels. We will then use this data to present detailed multi-spacecraft observations of the solar energetic proton events starting December 7 and 13, 2006 and their entry into the magnetosphere to L=4.