Abstract
Abstract. The main part of the Cluster Spatio-Temporal Analysis of Field Fluctuations (STAFF) experiment consists of triaxial search coils allowing the measurements of the three magnetic components of the waves from 0.1 Hz up to 4 kHz. Two sets of data are produced, one by a module to filter and transmit the corresponding waveform up to either 10 or 180 Hz (STAFF-SC), and the second by the onboard Spectrum Analyser (STAFF-SA) to compute the elements of the spectral matrix for five components of the waves, 3 × B and 2 × E (from the EFW experiment), in the frequency range 8 Hz to 4 kHz. In order to understand the way the output signals of the search coils are calibrated, the transfer functions of the different parts of the instrument are described as well as the way to transform telemetry data into physical units across various coordinate systems from the spinning sensors to a fixed and known frame. The instrument sensitivity is discussed. Cross-calibration inside STAFF (SC and SA) is presented. Results of cross-calibration between the STAFF search coils and the Cluster Fluxgate Magnetometer (FGM) data are discussed. It is shown that these cross-calibrations lead to an agreement between both data sets at low frequency within a 2% error. By means of statistics done over 10 yr, it is shown that the functionalities and characteristics of both instruments have not changed during this period.
Highlights
Data calibration of spectra and waveforms issued from a search coil magnetometer is not a new problem
The technology used in CLUSTER–Spatio-Temporal Analysis of Field Fluctuations (STAFF) experiments has been substantially upgraded since this epoch, but the principle remains the same: how to calibrate magnetic waveforms issued from a search coil rotating across a high ambient DC field, knowing that the transfer function varies with the frequency? This kind of problem has been solved in this epoch for time– frequency studies (Robert et al, 1978, 1979)
A method to calibrate the waveform delivered by a rotating search coil has been proposed, and used for CLUSTER– STAFF-SC data
Summary
Data calibration of spectra and waveforms issued from a search coil magnetometer is not a new problem. Robert et al.: CLUSTER–STAFF search coil magnetometer calibration field components in this plane, and so compare them with a fluxgate magnetometer instrument This was done in the GEOS epoch, where the agreement found was ∼ 4 % in magnitude and ∼ 4◦ in direction (Robert, 1979b). A special effort to compare STAFF-SC data with the FGM onboard flux gate magnetometer data (Balogh et al, 1997, 2001) has been undertaken from the beginning of the mission until now. This was encouraged by the Cluster Active Archive (CAA) activities and by the organisation of regular cross-calibration meetings.
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