Recalibration of the long-term NOAA/MEPED energetic proton measurements

The MEPED instruments onboard the low-altitude polar orbiting NOAA/POES satellites have measured energetic particles since 1978, offering a nearly continuous series of energetic particle fluxes in the magnetosphere during three solar cycles. However, there are several problems in using these data for long-term studies, the most significant one being that the solid state detectors of the MEPED proton instruments suffer significant radiation damage. This causes the effective energy thresholds of the instrument to increase, leading to underestimated particle fluxes already a couple of years after satellite launch. Before the MEPED data can reliably be used in any long-term study the data have to be recalibrated taking into account the decay of the detectors. In this paper we present quantified estimates of the degree of radiation damage for all NOAA/POES satellites, a method for correcting the MEPED proton measurements, and give an estimate of energetic proton fluxes from 1978 to present.