PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT PUBLICATION_DATE = 2004-03-03 NOTE = "Description of aspects of MAG data." END_OBJECT = TEXT END Magnetic-field units ==================== The units of the preprocessed magnetic-field data are given as nanoTesla (nT). They represent the X, Y, and Z sensor values at the given time. These values were converted into nT using the following: FGM and VHM: nT = (value - 8192) / 8192 * factor, The value of the factor is determined from the range given with each vector using the following table: Range FGM Factor VHM Factor 0 40 32 1 400 256 2 10000 - 3 44000 - MAGStatus ========= The MAGStatus data are an array of bits that describe the status of the MAG equipment, as set out in the following table. FIELD SIZE NAME BYTE BIT PacketType 1 Housekeeping/Science-data flag 0 7 MSB SCAS 1 SCAS status 0 6 AverageType 1 Average Type (fixed/running) 0 5 SHMFlag 1 SHM Flag 0 4 VHMFlag 1 VHM Flag 0 3 FGMFlag 1 FGM Flag 0 2 ADCFlag 1 ADC Flag 0 1 MCI 9 Measurement Cycle Interrupt 0-1 0,7-0 LSB,MSB Average 5 TimeCode Missing 2 2 sparebits 2 spare two bits 2 1-0 BIU Discretes 34 16 PROM 1 PROM program 3 7 MSB ConfigEnable 1 Config-Enable 3 6 PSU_2 1 PSU 2 3 5 PSU_1 1 PSU 1 3 4 Processor_B 1 Processor B 3 3 Processor_A 1 Processor A 3 2 SleepMode 1 Sleep Mode 3 1 Reset 1 Reset 3 0 LSB FGMStatus ========= The FGMStatus data are an array of bits that describe the status of the FGM, as set out in the following table. FIELD SIZE NAME BYTE BIT rg 2 Range 0 7-6 MSB IFCFlag 1 IFC Flag on/off 0 5 autorange 1 AutoRange on/off 0 4 TimeStatus 4 time quality status 0 3-0 LSB sparebyte 8 spare bits 1 7-0 CalibId 8 Calibration Id 2 7-0 CoordId 8 Field Angle data 2 7-0 VHMStatus ========= The VHMStatus data are an array of bits that describe the status of the VHM, as set out in the following table. FIELD SIZE NAME BYTE BIT rg 1 Range (debugging only) 0 7 MSB TimeStatus 4 time quality status 0 6-3 sparebits 2 spare bits 0 2-0 LSB Digital 8 Digital Status word 1 7-0 CalibId 8 Calibration Id 2 7-0 CoordId 8 Field Angle data 3 7-0 MAG times ========= The Cassini spacecraft clock (SCLK) is a counter that advances by one tick every 1/256 seconds. SCLK times represent the number of elapsed seconds since the epoch 00:00:00 1 January 1958. They have the format ssss:ttt, in which ssss specifies the number of full seconds that have elapsed and ttt indicates by how many ticks the clock has advanced towards the next second. SCLK times may also include a partition number: p/ssss:ttt. This number is initially 1 but is incremented during the mission if the SCLK counter is reset or somehow interrupted or altered. The following discussion assumes a partition number of 1. For other partition numbers, the determination of SCLK times requires knowledge of the time at which the current partition was initiated. SCLK times are commonly recorded in MAG files as seconds since the epoch 00:00:00 1 January 1958. Time may also be represented in MAG files as Spacecraft Event Time (SCET) which, for Cassini, is Universal Time Coordinated (UTC). The relationship between SCLK and SCET/UTC is dependent on the count rate of the Cassini SCLK. Like most counter-based clocks, this rate is not constant but drifts with time. Consequently, conversion of SCLK times to SCET/UTC times requires knowledge of the drift rates. These rates are recorded in the SCLK/SCET coefficients file maintained by the Cassini Spacecraft Operations (SCO) team at JPL. As the Cassini mission progresses the difference between SCLK and SCET will typically be of order tens of minutes. Times in MAG data files ----------------------- The times associated with magnetic-field vectors in MAG data files are SCLK seconds since epoch 1958. The times associated with magnetic-field scalar values in MAG data files are SCET in seconds since epoch 2000 in TAI (International Atomic Time) Times in MAG header files ------------------------- FIRST TIME SCLK time of first record in data file; derived from primary header of CHDO file LAST TIME SCLK time of last record in data file; derived from primary header of CHDO file SCLK (in ABSTRACT) SCLK count obtained from tertiary header of CHDO file; also converted into year, day of year, month, date, time format; may differ from FIRST TIME by some minutes SCET (in ABSTRACT) year, day of year, month, date, time format; determined from corrected SCLK count; also converted into an equivalent SCET count of seconds since 1958 Times in MAG label files ------------------------ START_TIME SCLK time of first record in data file; obtained from FIRST TIME in flatfile header STOP_TIME SCLK time of last record in data file; obtained from LAST TIME in flatfile header SPACECRAFT_CLOCK_START_COUNT SCLK (epoch 1958) count of first record in data file; determined from SPICE utility CHRONOS using START_TIME; format p/ssss.ttt SPACECRAFT_CLOCK_STOP_COUNT SCLK count of last record in data file; determined from SPICE utility CHRONOS using STOP_TIME; format p/ssss.ttt SCLK (in NOTE) SCLK count obtained from tertiary header of CHDO file; also converted into year, day of year, month, date, time format; obtained from flatfile-header ABSTRACT; may differ from START_TIME by some minutes SCET (in NOTE) year, day of year, month, date, time format; determined from corrected SCLK count; also converted into an equivalent SCET count of seconds since 1958; obtained from flatfile-header ABSTRACT