ROSETTA ROMAP DATA CALIBRATION DESCRIPTION =========================================================================== Revisions --------- 2009-04-20 first issue, xxx Purpose ------- This document describes the calibration of the ROMAP-MAG and ROAMP-SPM data delivered in the ROMAP level 3 data set. ROMAP-MAG calibration ===================== Introduction ------------- There are 2 kinds of calibrations applied to the ROMAP-MAG raw data: 1) Preliminary calibrated magnetometer data (draft aligned and very draft offset corrected). 2) Final calibration (cleaned from offset and spacecraft disturbances, done by TU-BS using RPC data). Only some selected data intervals are provided to PSA during cruise. The cleaning procedure consists of the following steps: - Disturbances which can de identified as lander supply current related are removed first. Only stepwise switched currents can be removed. The step height is determined as good as possible, Step times are determined and a function with constant bias fields between step times is created which is subtracted from the original data. - High frequent disturbances are identified by evaluation of dynamic spectra. If significant high frequent disturbances can be identified (during cruise in always due to reaction wheels) data are filtered down to 1Hz data (0.5Hz corner frequency) - Interferences due to orbiter sources are determined by comparison of RPC-MAG and ROMAP data. If signals occurs at both sensors with different signal amplitude (can be seen in difference) the ratio is determined, the disturbance signal is scaled for both sensors and the scaled signals are subtracted from the data. - Finally the offsets are determined with best effort. For that a solar wind analysis is used. For flybys solar wind data before and after are needed to interpolate the offset during flyby. Only final level 3 data, no intermediate products or correction functions are archived. Level 3 data are only produced for selected time intervals (e.g. Mars flyby, Steins flyby). Preliminary calibration (level 3 A, B and C) ----------------------------------------------- The preliminary calibration is used during cruise phase when sensorhead boom is stowed. The calibration parameters are the rotation matrix (from ROMAP sensor system to Lander system and Orbiter system) and the offset vector. The offset vector is generally time dependent. However, unless otherwise specified, a constant offset vector is used. In the level 3 data the disturbances due to MUPUS instrument are not removed. Level 3 A --------- Calibration in ROMAP system (R). Boom stowed. (BRx_cal) ( 1 0 0 ) (BRx + 700 ) (BRy_cal) = ( 0 1 0 ) . (BRy + 1400 ) (BRz_cal) ( 0 0 1 ) (BRz - 1100 ) where BR_cal is the calibrated magnetic field vector in the ROMAP system. BR is the raw magnetic field vector in the ROMAP system. The unit for BL, BR, BR_cal and offset is nT. Level 3 B --------- Calibration in the Lander system (L). Boom stowed. (BLx_cal) ( 0 0.33569 -0.94197 ) (BRx + 700 ) (BLy_cal) = ( 1 0 0 ) . (BRy + 1400 ) (BLz_cal) ( 0 0.94197 0.33569 ) (BRz - 1100 ) where BL_cal is the calibrated magnetic field vector in the Lander system BR is the raw magnetic field vector in the ROMAP (sensor) system : The unit for BL, BR, BL_cal and offset is nT. Level 3 C --------- Calibration in the S/C (Orbiter) system. Boom stowed. The calibrated magnetic field vector in the Orbiter system (BO) is given by the following transformation of the magnetic field vector in the ROMAP system (BR): ( 0 -0.3357 0.942 ) Bs/c_cal = ( -1 0 0 ) . (BR - Boffset) ( 0 0.942 0.3357 ) where Bs/c_cal is the calibrated magnetic field vector in the S/C system BR is the raw magnetic field vector in the ROMAP (sensor) system Boffset is the offset vector in ROMAP system. The unit for BR, Bs/c_cal and Boffset is nT. The offsets used for converting data from CODMAC level 2 to CODMAC level 3 (C type files in ROMAP notation) and the corresponding data products are listed below. Mars phase: MAG_FSC_060829181608_00087 MAG_FSC_061128162210_00088 ( -900) Boffset= (-1400) ( 1050) MAG_FSC_061206010011_00009 MAG_FSC_061206011057_00018 MAG_FSC_061206013312_00009 MAG_FSC_061206014352_00018 ( -900) Boffset= (-1440) ( 1070) MAG_FSC_061206070011_00009 MAG_FSC_061206071051_00018 MAG_FSC_061206073311_00077 ( -895) Boffset= (-1435) ( 1066) MAG_FSC_061207030011_00029 MAG_FSC_061207033312_00697 ( -885) Boffset= (-1405) ( 1054) MAG_FSC_061208000208_00121 MAG_FSC_061208034806_00039 MAG_FSC_070224010108_02212 MAG_FSC_070522142206_00121 ( -900) Boffset= (-1400) ( 1050) Steins phase: MAG_FSC_080904183821_02039 ( -550) Boffset= (-1800) ( 1200) Level 3 D --------- Calibration in the ECLIPJ2000 system. Boom stowed. The magnetic field vectors are transformed from orbiter system (level 3 C) to the ECLIPJ2000 reference frame. The rotation matrix is time dependent. Final calibration (level 5 E, F and G) -------------------------------------- Level 5 E --------- Final calibrated data, in physical units, cleaned from offset and spacecraft disturbances, in MAG (magnetometer) coordinates Level 5 F --------- Final calibrated SC data, in physical units, cleaned from offset and spacecraft disturbances, in Lander coordinates Level 5 G --------- Final calibrated SC data, in physical units, cleaned from offset and spacecraft disturbances, in S/C coordinates Level 5 H --------- Final calibrated SC data, in physical units, cleaned from offset and spacecraft disturbances, in ECLIPJ2000 coordinates. ROMAP-SPM calibration ===================== Introduction ------------- The level 3 calibration consists of: - conversion of ion energy and angle distributions in cm-2*s-1, - conversion of Faraday cup currents in nA, - conversion of energy in eV - conversion of angle (elevation) in degrees. The ion currents are left in ADC units (signed 16 integers) since the CEM amplifications are not yet clear. Energy and angle conversion --------------------------- The energy tables and the correspondences between step numbers and energy and between step numbers and angle (elevation) are given in the following tables. Correspondence between step number and elevation: Step No | Ion1/2 (deg) ========|============= 0 | -52 1 | -47 2 | -41 3 | -34 4 | -27 5 | -21 6 | -16 7 | -11 8 | -6 9 | 0 10 | 5 11 | 10 12 | 15 13 | 20 14 | 25 15 | 31 Correspondence between step number and energy: Step No "64" | Step No "32" | Ion1/2 (eV) | Electron (eV) =============|==============|=============|============== 0 | 0 | 38.6 | 0.35 1 | | 42.6 | 0.42 2 | 1 | 46.6 | 0.49 3 | | 50.6 | 0.56 4 | 2 | 54.6 | 0.63 5 | | 59.9 | 0.7 6 | 3 | 65.3 | 0.84 7 | | 70.6 | 0.98 8 | 4 | 77.3 | 1.12 9 | | 83.9 | 1.3 10 | 5 | 90.6 | 1.47 11 | | 98.6 | 1.75 12 | | 107 | 2.03 13 | 6 | 117 | 2.38 14 | | 127 | 2.74 15 | 7 | 138 | 3.16 16 | | 150 | 3.72 17 | 8 | 163 | 4.28 18 | | 178 | 4.98 19 | 9 | 194 | 5.82 20 | | 211 | 6.73 21 | 10 | 230 | 7.79 22 | | 250 | 9.05 23 | 11 | 271 | 10.5 24 | | 295 | 12.3 25 | 12 | 321 | 14.2 26 | | 350 | 16.5 27 | 13 | 381 | 19.2 28 | | 414 | 22.3 29 | 14 | 450 | 25.9 30 | | 490 | 30.1 31 | 15 | 533 | 34.9 32 | | 580 | 41 33 | 16 | 640 | 47.4 34 | | 700 | 54.7 35 | 17 | 760 | 63.1 36 | | 820 | 73.7 37 | 18 | 900 | 86.3 38 | | 980 | 100 39 | 19 | 1060 | 116 40 | | 1160 | 135 41 | 20 | 1260 | 156 42 | | 1360 | 181 43 | 21 | 1480 | 211 44 | | 1620 | 245 45 | 22 | 1760 | 284 46 | | 1920 | 330 47 | 23 | 2080 | 383 48 | | 2260 | 445 49 | 24 | 2460 | 517 50 | | 2680 | 600 51 | 25 | 2920 | 695 52 | | 3180 | 810 53 | 26 | 3460 | 937 54 | | 3760 | 1095 55 | 27 | 4080 | 1274 56 | | 4440 | 1474 57 | 28 | 4820 | 1716 58 | | 5260 | 1989 59 | 29 | 5720 | 2316 60 | | 6220 | 2684 61 | 30 | 6760 | 3115 62 | | 7360 | 3621 63 | 31 | 8000 | 4210 Step No "64" | Step No "32" | Far.Cup -"Ions" (eV) | Far.Cup -"Electr" (eV) 0 | | 10.7 | 1 1 | 0 | 12.7 | 2 2 | | 15 | 3 | 1 | 17.6 | 4 | | 20.8 | 5 | 2 | 24.6 | 6 | | 29.2 | 7 | 3 | 34.6 | 8 | | 40.8 | 9 | 4 | 48.6 | 10 | | 57.6 | 11 | 5 | 67.8 | 12 | | 80.2 | 13 | 6 | 95.2 | 14 | | 113 | 15 | 7 | 133 | 16 | | 160 | 17 | 8 | 190 | 18 | | 224 | 19 | 9 | 264 | 20 | | 314 | 21 | 10 | 370 | 22 | | 440 | 23 | 11 | 520 | 24 | | 614 | 25 | 12 | 730 | 26 | | 864 | 27 | 13 | 1020 | 28 | | 1204 | 29 | 14 | 1430 | 30 | | 1690 | 31 | 15 | 2000 | Conversion of ion energy and angle distributions (ion 1 and ion 2) ------------------------------------------------------------------ N[particles/cm-2/s]= C/S/T Where C represent the counts (read from telemetry). S is the ion detector surface: ion1: 0.08 cm-2 ion2: 0.1 cm-2 T is the exposition time (read from the header of the ROMAP TM packets) short: 0.04 s long: 0.2 s Conversion of Faraday cup currents ---------------------------------- The currents are given by the Ohm law, I=U/R, where R = 5.1e9 Ohm U is given by the ADC; the ADC input range is [-2 V, 2 V] and the output resolution is 16 bits. Thus, the following transfer function is applied: R = 5.1e9 Ohm; U = (4.0/65535.0)*Itm -2.0, where Itm is the raw current (read from telemetry, i.e. ADC output) Ifc [nA] = (U/R)*1e9;