Investigation of a discrepancy between magnetic field magnitudes determined by the FGM and EDI instruments Jonny Gloag, Edita Georgescu, Elizabeth Lucek, Chris Carr 26th October 2006

CAA cross-calibration meeting A result from the previous cross-cal meeting A systematic shift can be seen in ratio of EDI to FGM |B| This could be due to an incorrect FGM gain. The shift here is ~0.2% This could possibly be explained by the temperature dependence of the FGM sensor gains.

CAA cross-calibration meeting Ground calibration temperature dependence Find in-flight temperatures for each sc. Use established ground determined gains as starting point. Use ground determined temperature coefficients which depend on: –Spacecraft –Range(2-3 and 4-5) –Sensor axis

CAA cross-calibration meeting New gains at operational temperature s/crangesensortemp coef sensitivity at 19.5degC sensitivity at -19 degCsensitivity at -10 degCNew gain 12x E x E x E y E y E y E z E z E z E x E x E x E y E y E y E z E z E z E

CAA cross-calibration meeting Solar wind analysis Calibration in EDI Fourier analysis (Kepko et al. 1996) Jumps at range changes Refinement files to compensate for short term variations in calibration Spin axis offsets Bulk of cal. set Tweaks to some cal. Calibration overview and results with new gains Intercalibration on selected data periods Tweaks to some cal.

CAA cross-calibration meeting EDI/FGM plots for 2 selected days sc 1

CAA cross-calibration meeting EDI/FGM plots for 2 selected days sc 2

CAA cross-calibration meeting EDI/FGM plots for 2 selected days sc 3

CAA cross-calibration meeting Alteration of sensitivities to compensate for 0.2% shift in magnitude ratio Multiply cal. matrix and offsets by diagonal matrix. FGM and EDI ratio is closer to a value of 1. Unfortunately gives no improvement to calibration

CAA cross-calibration meeting Summary A discrepancy has been found between EDI and FGM field magnitude measurements FGM sensor gains have been modified to reflect operational temperatures Correction to ratio of EDI/FGM field magnitude is in the correct direction but too big. It is possible to force EDI and FGM magnitudes to be approximately the same by using the shift in ratio of magnitudes. Unfortunately this does not give us a result to improve the FGM calibration.

CAA cross-calibration meeting Work presented by the EDI team at the previous cross-calibration meeting, showed a discrepancy between magnetic field magnitudes determined by FGM and EDI. An investigation has been carried out between the EDI and FGM teams to test if the ground measured temperature dependence of the FGM sensor gains could explain this discrepancy and the results are presented here. ABSTRACT