STAFF Instrument Calibration, Sensitivity, and Performance Evolutions During the Cluster Mission

Abstract

The Spatio‐Temporal Analysis of Field Fluctuations (STAFF) instruments onboard the Cluster satellites were designed to measure magnetic fluctuations in the 0.2–12 Hz and 0.2–180 Hz frequency ranges from the Search‐Coil Magnetometer (SCM), as well as electromagnetic spectra from the Spectrum Analyzer (SA) in the 8–4,000 Hz range. They provided a considerable amount of data throughout the 24‐year mission. The production and calibration of these data sets were detailed in Robert et al. (2014, https://doi.org/10.5194/gi‐3‐153‐2014 ), which demonstrated its excellent quality and good agreement with the fluxgate magnetometer (FGM) measurements over their common frequency range. The Cluster's 24 years of operation, which far exceed the nominal 2‐year mission, represent the longest flight of search coil magnetometers and offer a unique opportunity to evaluate their performance over such a long period, as well as to compare the results of four initially identical instruments. The present work, based on data now archived at the Cluster Scientific Archive (CSA), examines the evolution of these products after the first 11 years in space, and until the end of the Cluster operations in September 2024. The quality of the measurements, calibration, sensitivities, and their agreement between spacecraft proved to be excellent and remained stable throughout the mission. Comparison of spectra derived from the calibrated waveforms of STAFF (CWF) and FGM shows a very good agreement until the end of operations, a further proof of the high quality of their respective calibrations.