Intercalibration of GOES 8–15 solar proton detectors

Abstract

This work provides a relative intercalibration of the high‐energy proton channels from the Energetic Particle Sensors (EPS) flown on the Geostationary Operational Environmental Satellites (GOES) since 1994 using a technique that depends on features that arise during high solar wind dynamic pressure. Based on observations of solar energetic protons from polar‐orbiting and geostationary satellites (1998–2013), solar proton fluxes are isotropic at geostationary orbit during periods of high solar wind dynamic pressure (Pdyn>5−10 nPa). The observed isotropy results from the solar proton fluxes having rigidities (momenta per unit charge) greater than their geomagnetic cutoffs over the complete energy and angular responses of the satellite‐borne detector. (The cutoff in a given direction is the rigidity below which an interplanetary particle cannot reach that location.) Under these conditions, we determine the relative responses of the EPS flown on GOES 8 through 15. These detectors are widely used for alerts of the radiation hazard posed to spacecraft and humans by solar energetic particle events; therefore, it is important to know their relative responses. The results of this low‐scatter intercalibration analysis show that the relative responses agree to 20% or better (sometimes better than 1%). The effect of such relative calibration differences on the derived integral fluxes used by NOAA for its real‐time solar radiation storm alerts is shown to be small (<10%). This method can be used to intercalibrate solar proton detectors of different design if their broad energy response functions are carefully accounted for.