In-flight calibration of NOAA POES proton detectors: Derivation of the MEPED correction factors

TL;DR

This paper presents a new in-flight calibration method for NOAA POES proton detectors that accounts for degradation over time, enabling accurate long-term proton flux measurements and improving electron data quality.

Contribution

The study introduces a robust calibration approach to derive correction factors for proton detectors, including the highest-energy channels, using satellite comparisons over time.

Findings

Derived correction factors for proton detectors over a year.

Validated the calibration method with consistent results across satellites.

Enabled quantitative long-term proton flux studies.

Abstract

The MEPED instruments on board the NOAA POES andMetOp 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.