Data Set Overview : This dataset contains data acquired by the Galileo Magnetometer from the Earth 1 encounter. The data have benn averaged down to twenty second resolution from the 7.68 kB Low Rate Science (LRS) real time telemetry mode. These data have been fully processed to remove instrument response function characteristics and interference from magnetic sources aboard the spacecraft. The data are provided in both Geocentric Solar Ecliptic (GSE) and Geocentric Solar Magnetic (GSM) coordinates. Trajectory data has been attached to this data for easier use. Trajectory data which was at a sample rate of once per minute, was linearly interpolated to match the 20 second sample rate of this data. Primary Reference: [KIVELSONETAL1993] Data : ----------------------------------------------------------------- Table 1. Data record structure ----------------------------------------------------------------- Column type description ----------------------------------------------------------------- time char S/C event time (UT) in PDS time format: yyyy-mm-ddThh:mm:ss.sssZ Bx float X component GSE or GSM coords. (20s res)  By_gse float Y component GSE coordinates (20s res)  Bz_gse float Z component GSE coordinates (20s res)  By_gsm float Y component GSM coordinates (20s res)  Bz_gsm float Z component GSM coordinates (20s res)  Bmag float |B| Magnitude of B (20s res)  stBx float Standard deviation for: Bx  stBy_gse float Standard deviation for: By_gse  stBz_gse float Standard deviation for: Bz_gse  stBy_gsm float Standard deviation for: By_gsm  stBz_gsm float Standard deviation for: Bz_gsm  stBmag float Standard deviation for: Bmag  npts int Points in average dqf int Data quality flag X float X component GSE and GSM  Y_gse float Y component GSE coordinates  Z_gse float Z component GSE coordinates  Y_gsm float Y component GSM coordinates  Z_gsm float Z component GSM coordinates  Data Acquisition: The data for this dataset were acquired as part of the normal instrument calibration activities associated with the cruise to Jupiter. As such, the instrument was commonly configured in modes which required calibration even though they may not have been the optimal mode for science data acquisition. The Galileo magnetometer has 8 possible LRS acquisition configurations (modes). There are two sensor triads mounted 7 and 11 meters from the rotor spin axis (inboard and outboard) along the boom. Each of the sensor triads has two gain states (high and low). In addition, the sensor triads can be 'flipped' to move the spacecraft spin-axis aligned sensor into the spin plane and visa versa. Please see the instrument description for full details on the instrument, sensors, and geometries. The combinations of sensor, gain state, and flip direction form modes. ------------------------------------------------------------------ Table 2. Mode Characteristics ------------------------------------------------------------------ Mode Name Acronym range quantization ------------------------------------------------------------------ Inboard, left, high range* ILHR +/- 16384 nT 8.0 nT Inboard, right, high range* IRHR +/- 16384 nT 8.0 nT Inboard, left, low range* ILLR +/- 512 nT 0.25 nT Inboard, right, low range* IRLR +/- 512 nT 0.25 nT Outboard, left, high range* ULHR +/- 512 nT 0.25 nT Outboard, right, high range* URHR +/- 512 nT 0.25 nT Outboard, left, low range* ULLR +/- 32 nT 0.008 nT Outboard, right, low range* URLR +/- 32 nT 0.008 nT ------------------------------------------ Table 3. Mode change history ------------------------------------------ s/c clock date/time mode ------------------------------------------ 00562976:00:0 90-305/16:31 ULHR 00572976:00:0 90-316/17:00 ULLR 00578673:00:0 90-320/17:00 URLR 00586204:00:0 90-325/23:55 URHR 00592915:00:0 90-330/17:01 ILLR 00597439:00:0 90-333/21:15 IRLR 00610156:00:0 90-342/19:33 IRHR 00610509:00:0 90-343/01:30 IRLR 00615701:00:0 90-346/17:00 URLR 00618550:00:0 90-348/17:00 URHR 00624261:00:0 90-352/17:15 ULHR * range is the opposite of gain In addition to exercising the various instrument modes during the first earth encounter, numerous instrument calibration activities were performed. These include using both the internal and external calibration coils. Data corrupted by the use of the calibration coils or by the flipper motor have been removed from the processed data. These data have been archived with the Experimenter Data Records (EDR) and other Magnetometer team raw data archive products. Data Sampling: These data have been resampled to 20 seconds using overlapping 40 second averages of the high-resolution (~2/3 second) data. The time tag represents the center of the averaging interval. For a discussion regarding the high-resolution data please refer to the catalog file for the GO-E-MAG-3-RDR-E1-HIGHRES-V1.0 data set (/CATALOG/MAG_E1_HIGHRES_DS.CAT). Coordinate Systems : Geocentric Solar Ecliptic (GSE) and Geocentric Solar Magnetic (GSM) are related earth centered coordinate systems. Both the GSE and GSM X directions are taken along the Earth - Sun line, positive towards the Sun. The GSE Z direction is parallel to the ecliptic normal, positive northward, and Y completes the right-handed set (towards dusk). For GSM, the X-Z plane contains the Earth's dipole moment vector, positive northward, and Y completes the right-handed set. GSE coordinates are commonly used for analyzing the solar wind near the Earth and GSM coordinates are used when analyzing data inside the Earth's bow shock. Data Processing : These data have been processed from the PDS dataset: 'GO-E/V/A-MAG-3-RDR-HIRES-V1.0' In order to generate the IRC processed dataset, the following procedure was followed: 1) Sensor zero level corrections were subtracted from the raw data, 2) Data were converted to nanoTesla, 3) A coupling matrix which orthogonalizes the data and corrects for gains was applied to the data (calibration applied), 4) Magnetic sources associated with the spacecraft were subtracted from the data, 5) Data were 'despun' into inertial rotor coordinates, Lastly, in order to generate the processed data in GSE/GSM coordinates the data were transformed into geophysical coordinates and averaged to twenty second resolution. For a more detailed description of these proceedures please refer to the file /CALIB/HR_PROC.TXT. For more information regarding data calibration please refer to [KEPKOETAL1996].

Review : These data have been reviewed by the instrument team and are of the highest quality that can be generated at this time. Science results based on some of these data have been published in several journals (Science, JGR, etc.). After submission to PDS, these data successfully completed the peer review process. Confidence Level Overview : Each aspect of the data processing sequence can be analyzed to determine its maximum possible error contribution. In theory, these errors could be summed to provide estimates of the maximum error for each data point. Error analysis for these data have not been taken to that level. The MAG team believes that calibrations (sensor geometry and gains) are good enough that they produce a negligible source of data error. In addition, that the coordinate system transformations which are derived from the SPICE kernels and Toolkit are believed to be negligible sources of error in the magnetic field vectors. The most significant sources of error are those associated with magnetic sources aboard the spacecraft, especially those with temporal or spacecraft orientation variations. The next greatest contributor of error is the data from the AACS which affects our knowledge of the spacecraft orientation and hence rotates the magnetic field vector. Lastly, telemetry or software errors which produce 'spikes' or bit errors in the data are error sources. Data Coverage and Quality : In regions where the magnetic sources associated with the spacecraft are fairly constant, magnetic interference is probably reduced by data processing to better than 0.05 nT at the inboard sensors. In these same regions, sensor zero levels (offsets) are known equally well. The data processing software does a fairly good job of removing all currently identified sources of magnetic interference. However, there are some time intervals when the zero levels of the spin plane sensors show large variations (1-5 nT) on short time scales (minutes to hours). After a while (hours to days) the offsets return to their nominal levels. The source of these magnetic fields has not yet been identified. The method of removing offsets from the spin plane sensors does remove these effects, but the method of determining the spin axis aligned sensor offsets does not. In regions where large variations are detected in the spin plane sensors it is reasonable to assume that similar variations are taking place in the spin axis aligned sensor. Averaging reduces the level of the interference, though it may not remove it completely. A second problem in determining and removing the magnetic interference associated with the spacecraft is the movement of these magnetic sources. At the Earth 2 encounter an extensive test was done to determine the interference patterns as a function of the position of the magnetic sources. Data was taken with the scan platform at fifteen degree intervals and the interference was successfully modeled. However, this test was not done for the Earth 1 encounter. After processing the data it is apparent that there is a small time variation in the spacecraft magnetic interference signature. As a result there is still a small amount of magnetic interference left in the Earth 1 encounter data. Also contributing to interference problems is the energetic particle detector. Interference from this source has been removed only from the data on day of year 342 of 1990. By looking at the dynamic spectra of the data remaining interference can be detected. Limitations : MAG data processing software creates a data quality flag (DQF) which is an assessment of AACS and telemetry error source contamination of a given data point. This number is binary integer where each bit indicates the presence or absence of some error source. A DQF is assigned to each point of the high-res (about 2/3 sec) data. The values given in this data set is the highest value for the averaged interval. The number 0 represents the absence of all error sources which are tested. The higher order bit (larger number) error sources are considered to be more significant error sources. Data are examined for gradients in the field which might be associated with telemetry bit errors, for regions of bad AACS angles, and for completely missing data. If the error is considered completely unrecoverable, the data values are replaced with a missing data flag. In the case of a flag in the rotor spin angle, the vector components may be flagged but the magnitude is still valid. Table 4 is a list of all of the error checks and the bits they set in the DQF field. ------------------------------------------------------------------ Table 4. Data Quality Flag (DQF) Values ------------------------------------------------------------------ DQF_GOOD_DATA 0 Good data DQF_BX_GRAD_WARNING 2^0 Component gradient warning DQF_BY_GRAD_WARNING 2^1 Component gradient warning DQF_BZ_GRAD_WARNING 2^2 Component gradient warning DQF_INTERP_ROTATTR 2^3 Missing rotor RA interpolated DQF_INTERP_ROTATTD 2^4 Missing rotor DEC interpolated DQF_INTERP_SPINDELT 2^5 Missing rotor Spin Delta interpolated DQF_INTERP_SCRELCON 2^6 Missing Relative Cone angle interpolated DQF_INTERP_SCRELCLK 2^7 Missing Relative Clock angle interpolated DQF_INTERP_ROTATTT 2^8 Missing rotor Twist interpolated DQF_INTERP_SPINANGL 2^9 Missing rotor Spin interpolated DQF_ROTATTR_FLAG 2^10 Missing rotor RA flagged DQF_ROTATTD_FLAG 2^11 Missing rotor DEC flagged DQF_SPINDELT_FLAG 2^12 Missing rotor Spin Delta flagged DQF_SCRELCON_FLAG 2^13 Missing Relative Cone angle flagged DQF_SCRELCLK_FLAG 2^14 Missing Relative Clock angle flagged DQF_ROTATTT_FLAG 2^15 Missing rotor Twist flagged DQF_AACS_TELEMETRY_HIT_FLAG 2^16 Telemetry hit in AACS record DQF_MAG_TELEMETRY_HIT_FLAG 2^17 Telemetry hit in mag record DQF_SPINANGL_FLAG 2^18 Missing rotor Spin flagged DQF_BX_GRAD_ERROR 2^25 Component gradient error DQF_BY_GRAD_ERROR 2^26 Component gradient error DQF_BZ_GRAD_ERROR 2^27 Component gradient error DQF_BX_FLAG 2^28 Component flagged DQF_BY_FLAG 2^29 Component flagged DQF_BZ_FLAG 2^30 Component flagged Magnetic field gradient warning or error levels are set during the data processing according to expected variances depending on the region of space. In the solar wind, gradient warnings are usually issued at gradients of 10 nT/sec and errors at 15 nT/sec. In the magnetosheath, these values may be 50 percent larger. In the inner magnetosphere, these dqf flags may be completely turned off. Similarly, AACS angles are interpolated across gaps during the processing if the gap length is relatively short (less than 10 minutes typically). If the gaps in spacecraft attitude are long, the AACS angles are flagged and not interpolated. Errors associated with AACS angles have various effects on the data. The rotor right ascension and declination are crucial to the understanding of the spacecraft orientation. Fortunately, these angles are slowly varying and can be interpolated to better than 1 degree of accuracy for long (many hour) time periods except near major spacecraft maneuvers. The relative clock and cone angles are used to remove scan platform interference. In their absence, no interference is removed (+/- 0.15 nT error possible in each component). The rotor motion spin delta is used to determine the instantaneous spin frequency for the phase delay computation. In its absence, the last known phase delay is applied to the current data point. The rotor spin angle and twist angle must be present in order to despin the data. These angles are generally not interpolated for more than ten minutes because the rotor spin period drifts over time periods on this order. On 1990-Dec-10 a thruster burn resulted in the loss of AACS data over several small intervals. Because the spacecraft is in a period of transition and the spin period is changing rapidly these gaps in AACS can not be accurately interpolated. Without knowledge of the spinangl, it is not possible to correctly despin the data. As a result of the loss of the spinangl the following time periods on Dec-10 have been deleted from the data set: 1990-Dec-10 7:05:00-7:08:05 1990-Dec-10 7:29:10-7:33:00 1990-Dec-10 7:53:40-8:09:00 Without knowledge of the spacecraft relative clock angle (screlclk) the spacecraft interference can not be removed. As a result of the loss of the clock angle no interference has been removed from the following time period: 1990-Dec-10 7:00:00-8:25:00