In‐flight calibration of NOAA POES proton detectors—Derivation of the MEPED correction factors

Abstract

The MEPED instruments on board the NOAA POES and MetOp satellites have been continuously measuring energetic particles in the magnetosphere since 1978. However, degradation of the proton detectors over time leads to an increase in the energy thresholds of the instrument and imposes great challenges to studies of long‐term variability in the near‐Earth space environment as well as a general quantification of the proton fluxes. By comparing monthly mean accumulated integral flux from a new and an old satellite at the same magnetic local time (MLT) and time period, we estimate the change in energy thresholds. The first 12 monthly energy spectra of the new satellite are used as a reference, and the derived monthly correction factors over a year for an old satellite show a small spread, indicating a robust calibration procedure. The method enables us to determine for the first time the correction factors also for the highest‐energy channels of the proton detector. In addition, we make use of the newest satellite in orbit (MetOp‐01) to find correction factors for 2013 for the NOAA 17 and MetOp‐02 satellites. Without taking into account the level of degradation, the proton data from one satellite cannot be used quantitatively for more than 2 to 3 years after launch. As the electron detectors are vulnerable to contamination from energetic protons, the corrected proton measurements will be of value for electron flux measurements too. Thus, the correction factors ensure the correctness of both the proton and electron measurements.

Magnetospheric conditions near the equatorial footpoints of proton isotropy boundaries

“…Specifically, for a different NOAA-type satellite the corresponding corrected energies were taken to be 30/80 keV (NOAA-19), 30/94 keV (NOAA-18), 36/92 keV (METOP-2) and 46/122 keV (NOAA-17). (Here we note that the corrected energy thresholds are slightly different for precipitated and trapped particles at every spacecraft and that improved correction factors have been recently published by Sadanger et al (2015). However, these differences do not seriously affect any of the results in our paper.…”

Energetic electron precipitation into the middle atmosphere—Constructing the loss cone fluxes from MEPED POES

“…The resulting fluxes represent the true electron fluxes in the respective energy bands (red line, Figure b). The importance of the correction of the proton flux spectrum is demonstrated in Figures 9 and 10 in Sandanger et al []. It is also demonstrated in Figure b.…”

“…(a) The uncorrected integral spectrum (blue line) has the nominal energy thresholds: 30, 80, 250, 800, and 2500 keV. In the corrected spectrum (red line) the energy thresholds has changed according to the correction factors found by Sandanger et al [] . The proton fluxes in the energy range from 210, 270, and 440 keV (marked as black vertical lines) to 2600 keV are subtracted from the original measured electron fluxes (blue line) in Figure b.…”

The Impact of Energetic Particle Precipitation on Mesospheric OH – Variability of the Sources and the Background Atmosphere

“…The two MEPED electron solid‐state detectors monitor the intensity of electrons in three nominal energy bands: >30, >100, and >300 keV (Evans & Greer, ), whose known data challenges have been catered for using the new analysis toolbox described by Nesse Tyssøy et al (). In this toolbox, the proton fluxes are corrected for degradation due to radiation damage by applying correction factors derived by Sandanger et al () and Ødegaard et al (). The corrected proton data are then used to correct the electron data from proton contamination.…”