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This description was generated automatically using input from the Planetary Data System. Data Set Overview ================= This data set contains magnetic field vectors acquired by the Galileo Orbiter magnetometer during the magnetospheric survey portion of the mission. These data were acquired in the optimal averager (opt/avg) and real-time survey (RTS) modes beginning during the Jupiter approach and continuing throughout Jupiter orbital operations. The data set covers the time period from 1995-11-06T00:21:30 UT (Jupiter approach) until the end of mission (September 2003). Sampling rates are variable and depended upon the downlink capabilities. With few exceptions, the data are provided at the full downlink resolution. The data are provided in five coordinate systems (IRC, System III [1965], JSE, JSO, and JSM). Parameters ========== Data Sampling ------------Data acquisition strategies varied throughout the mission. During the Jupiter approach period, most particles and fields (MWG) instruments were off while the magnetometer acquired low resolution opt/avg data. During the bulk of the prime mission, the MWG instruments were allowed to acquire continuous RTS data whenever the spacecraft was inside 50 Jovian radii (Rj). When the MWG was not returning RTS data, MAG used its opt/avg capability to acquire low time resolution averages of the field. In general, these are ~32 minute averages, although some higher rate data (1-8 minute) were used to fill small gaps in RTS data coverage. Early in the prime mission, MAG was required to 'pay' for the bits its used to return the opt/avg data by not acquiring as much high resolution data. MAG did not return data from the MWG transauroral crossing recorded interval in the C3 orbit so that it could have continuous coverage during that orbit. After the fourth orbit, the MAG opt/avg data was return in the spacecraft engineering data stream at no cost to the team. The MWG acquired RTS data beyond 50 Rj in selected bit rich orbits (G2, G7, G8, C9, C10) during the prime mission. RTS, opt/avg, and snapshot data were all stored in the MAG internal memory buffer. RTS data were continuously averaged at MAG memory address 4800 and transmitted to Earth in real-time. When an opt/avg ON command was given data were stored in the MAG memory buffer beginning at address 4800 and continuing to higher addresses until Opt/Avg OFF was commanded, another Opt/Avg ON was commanded and the MAG buffer began filling at 4800 again, or the MAG memory buffer filled. Opt/avg data was returned to Earth via Memory Read-Out (MRO) as telemetry permitted. Since RTS and opt/avg data used the MAG memory buffer in different ways, they could not be collected simultaneously. Snapshot data, which completely filled the MAG memory buffer, could likewise not be collected simultaneously with opt/avg, and caused periodic spikes in RTS data. Snapshot corruption of RTS data is discussed in more detail in the 'Data Quality and Coverage' section of this document. For a more detailed discussion how MAG RTS, opt/avg, and snapshot data are collected, please refer to [KIVELSONETAL1992]. When high-resolution data were available, but the RTS data were either lost or corrupted, simulated RTS (sRTS) data have been generated from the high-resolution data. sRTS data were averaged down to the RTS rate, then interpolated to be continuous with the existing RTS data. During the prime mission, the RTS data rate varied, depending the downlink capability. MAG has several different possible RTS data rates depending on the telemetry format: --------------------------------------------------------------------Table 1. MAG RTS Rates --------------------------------------------------------------------Format MAG bit rate Time between samples Corner Freq. (bps) (seconds) (mf) (Hz) --------------------------------------------------------------------A-D 2 24 36 1/34 E 4 12 18 1/34 F 6 8 12 1/17 G 8 6 9 1/17 H 12 4 6 1/17 I 18 8/3 4 1/17 Similarly, the opt/avg data can be acquired at different rates. The relatively high data rates fill the MAG internal memory buffer more quickly and are only used to cover short data disruptions. --------------------------------------------------------------------Table 2. Optimal Averager Data Rates --------------------------------------------------------------------Time between samples Buffer fill time Corner Freq. (RIM) ( (day/hh:mm) (Hz) --------------------------------------------------------------------1 00:01:00.67 03:22 1/67 2 00:02:01.33 06:44 1/134 4 00:04:02.67 13:29 1/268 8 00:08:05.33 1/02:58 1/536 16 00:16:10.67 2/05:56 1/1072 32 00:32:21.33 4/11:51 1/2144 64 01:04:42.67 8/23:42 1/4289 The instrument has the ability to acquire longer time averages but these modes were not used at Jupiter. After the prime mission ended (December 1997), RTS data acquisition was limited to only a few days near perijove except for a few orbits. RTS data are typically in the 2 bps (24 sec/sample) telemetry formats. Opt/avg data after end of the prime mission, are primarily provided in 32 RIM (~32 min/sample) averages. Both the opt/avg and the RTS data processor compute field averages by applying a recursive filter and decimate algorithm to the data. The instrument applies a calibration, decimates vectors down to minor frame (mf) samples (2/3 second) and despins the data using the spin angle value broadcast on the spacecraft bus. The corner frequencies of the recursive filter are provided in tables 1 and 2 for the various sample durations. The effect of this process is that the spacecraft time tags both RTS and opt/avg data at the time of decimation (end of average), rather than at the effective 'center' of the average. As a result there is a time shift or phase delay between RTS or opt/avg data and data (e.g. LPW) which have not undergone the same filtering process. The magnitude of the phase delay is dependent upon the averaging interval (or rate) and frequency content of the data. Analysis of the filter response to a wave at the spin period (dominant frequency) has determined that the phase delay may be eliminated with the correction: [Corrected time] = [Sample time] - (Rate * (1/3)) Where the 'Sample time' is the time assigned by the spacecraft, and the 'Rate' is the sampling rate in seconds. Both 'Sample Time' and 'Corrected Time' are provided in the data files. The IRC data file (which does not include a 'Corrected Time' column) contains a 'Spacecraft Clock' column which corresponds to the 'Sample Time' (and not the 'Corrected Time'). The RTS and opt/avg data overlay high time resolution data acquired at the same time best when the 'Corrected Time' is used. MAG uses fixed gains to acquire data [KIVELSONETAL1992]. Gain states must be manually changed by sending a gain change command to the instrument. There are 3 ranges of field strengths that the instrument can measure: --------------------------------------------------------------------Table 3. Magnetometer Ranges --------------------------------------------------------------------Field Range (nT) Magnetometer, range min max --------------------------------------------------------------------1/64 - 32 Outboard low field 1/4 - 512 Outboard high field, Inboard low field 8 - 16384 Inboard high field While the outboard magnetometer's position on the boom does make it less susceptible to spacecraft fields, its zero levels were less stable than those of the inboard magnetometer. As a result, the outboard magnetometer was generally not used except when the magnetic field strength was very low. The outboard magnetometer was typically only used outside of 60 Rj (in the low field range). From 9-60 Rj the inboard magnetometer, low field range was generally used. Inside of ~9 Rj the inboard magnetometer, high field range was used. Processing ========== Browse data are primarily processed onboard the spacecraft by using estimates of the instrument calibration and zero levels. The calibration estimates cannot be improved in post processing due to the onboard averaging. Any errors in the sensor zero levels in the spin plane sensors will appear as harmonics of the spin period, possibly modified by frequency folding effects associated with the averaging windows. These effects can be removed in the RTS data in post processing. The long average intervals of the opt/avg data effectively removes these problems without need for post processing. Improvements are made to the zero level correction of the spin aligned sensor data for both RTS and opt/avg data in post processing. Data ==== These data are stored in multiple data files in order to facilitate use and electronic distribution. In general, data from a single orbit is included in a data file. For some of the more data rich orbits, further subdivision was provided. Data from the five coordinate systems are stored in four separate files. The file format for a particular coordinate system is independent of the data acquisition interval. All data files from a given coordinate system are identical in structure. All data files are ASCII, fixed field, white space delimited tables. The following tables (4a-d) describe the record structure of the various type of data files. -------------------------------------------------------------------Table 4a. IRC Coordinates (Inertial Rotor coordinates) -------------------------------------------------------------------Column Type Description <units> -------------------------------------------------------------------samp time char spacecraft event time sample was acquired from MAG memory, PDS time format sclk char spacecraft clock (rim:mf:mod10:mod8) Bx_sc float magnetic-field spacecraft (IRC) x-component <nT> By_sc float magnetic-field spacecraft (IRC) y-component <nT> Bz_sc float magnetic-field spacecraft (IRC) z-component <nT> |B| float magnetic-field magnitude <nT> rotattr float rotor right ascension <degrees> rotattd float rotor declination <degrees> rotattt float rotor spin phase (twist) angle <degrees> spinangl float rotor spin phase angle <degrees> RATE float data sample rate <seconds> -------------------------------------------------------------------Table 4b. System III [1965] Coordinates -------------------------------------------------------------------Column Type Description <units> -------------------------------------------------------------------corr time char spacecraft event time of sample corrected for MAG filter response, PDS time format samp time char spacecraft event time sample was acquired from MAG memory, PDS time format Br float magnetic-field R (radial) component <nT> Btheta float magnetic-field theta (southward) component <nT> Bphi float magnetic-field phi (eastward) component <nT> |B| float magnetic-field magnitude <nT> R float s/c position - Radial distance from Jupiter center-of-mass <Rj = 71492 km> LAT float s/c position - latitude <degrees> ELON float s/c position - East longitude <degrees> WLON float s/c position - West longitude <degrees> -------------------------------------------------------------------Table 4c. Jupiter Solar Equatorial (JSE) Coordinates -------------------------------------------------------------------Column Type Description <units> -------------------------------------------------------------------corr time char spacecraft event time of sample corrected for MAG filter response, PDS time format samp time char spacecraft event time sample was acquired from MAG memory, PDS time format Bx float magnetic-field x (sunward) component <nT> By float magnetic-field y (duskward) component <nT> Bz float magnetic-field z (Jovian spin axis aligned) component <nT> |B| float magnetic-field magnitude <nT> X float s/c position - x (sunward) component <Rj> Y float s/c position - y (duskward) component <Rj> Z float s/c position - z (northward) component <Rj> LOCHOUR float s/c local hour <hours> -------------------------------------------------------------------Table 4d. Jupiter Solar Orbital (JSO) and Jupiter Solar Magnetic (JSM) Coordinates -------------------------------------------------------------------Column Type Description <units> -------------------------------------------------------------------corr time char spacecraft event time of sample corrected for MAG filter response, PDS time format samp time char spacecraft event time sample was acquired from MAG memory, PDS time format Bx float JSO/JSM magnetic-field x-component <nT> By_jso float JSO magnetic-field y-component <nT> Bz_jso float JSO magnetic-field z-component <nT> By_jsm float JSM magnetic-field y-component <nT> Bz_jsm float JSM magnetic-field z-component <nT> |B| float magnetic-field magnitude <nT> X float s/c position - JSO/JSM x-component <Rj> Y_JSO float s/c position - JSO y-component <Rj> Z_JSO float s/c position - JSO z-component <Rj> Y_JSM float s/c position - JSM y-component <Rj> Z_JSM float s/c position - JSM z-component <Rj> MLOCHOUR float S/C magnetic local hour <hours> These data were processed using SPICE kernels produced by the Galileo NAV team during the mission. All of the SPICE kernels used to produce this data set are contained on the MWG archive volume DVD in the EXTRAS/SPICE/KERNELS directory. The kernels (PDS PRODUCT_ID) used to create this were: S980326B.TSP - Prime Mission Reconstruction (JA-E12) S000131A.TSP - GEM reconstruction (E12-E26) S030916A.TSP - GMM (I27-J35) reconstruction PCK00007.TPC - Planetary constants kernel (2000-04-24) MK00062B.TSC - Galileo spacecraft clock kernel Coordinate Systems ================== The data are provided in five coordinate systems. Data are provided in the spacecraft coordinate system in order to aid in the interpretation of particle instrument data. The other coordinate systems are provided for use in Jovian magnetospheric studies. The Jupiter spin axis is defined to have a right ascension of 268.05 degrees and a declination of +64.49 degrees in the J2000 coordinate system used by SPICE. Inertial Rotor Coordinates (IRC) -------------------------------The IRC coordinate system takes the basic rotor coordinate system (Y along the boom, Z opposite the high gain antenna) which is spinning, and despins it using the rotor spin angle. For this reason IRC coordinates are sometimes referred to as 'despun spacecraft coordinates.' In this system, Z still points along the spin axis opposite the HGA (or roughly anti-Earthward), X is approximately parallel to the downward ecliptic normal, and Y completes the right handed set (pointing roughly towards dawn). System III [1965] Coordinates (SYS3) -----------------------------------SYS3 magnetic field vector components form the standard right handed spherical triad (R, Theta, Phi) for a Jupiter centered system. Namely, R is radial (along the line from the center of Jupiter to the center of the spacecraft), and positive away from Jupiter. Phi, the azimuthal component, is parallel to the Jovigraphic equator (Omega x R) and positive in the direction of corotation. Theta, the 'southward' component, completes the right handed set. For SYS3 trajectory both east and west longitudes are provided. West longitudes are related to east longitudes by to the algorithm: west longitude = 360. - east longitude <degrees> West longitude is defined such that it appears to increase with time for a stationary observer [DESSLER1983]. Note, however, that R, latitude, and west longitude constitute a left handed set. The SYS3 1965 prime meridian is the sub-Earth longitude of 1965-01-01 00:00 UT. The spin rate (which was determined from the rotation rate of the magnetic field) is 9 hrs 55 min 29.719 sec. (See [DESSLER1983] for a discussion on Jovian longitude). R is the radial (Jupiter's center to spacecraft center) distance. Latitude is planetocentric. Jupiter Solar Equatorial Coordinates (JSE) -----------------------------------------JSE is a Jupiter centered cartesian coordinates system defined to have it's Z-axis along the Jovian spin axis, positive in the direction of angular momentum (northward). The X-Z plane is contains the Sun so that the X-axis is the projection of the Sun direction into Jupiter's equatorial plane (positive towards the Sun). Y completes the right handed set and points duskward. This coordinate system is sometimes called Jupiter centered, Sun longitude fixed coordinates. Jupiter Solar Orbital Coordinates (JSO) --------------------------------------JSO is another Jupiter centered cartesian coordinate system. JSO is the equivalent at Jupiter of GSE coordinates system at Earth. In JSO coordinates, the X-axis points from Jupiter to the Sun. Z is parallel to the upward normal to Jupiter's orbital plane. Y completes the right handed set. Jupiter Solar Magnetic Coordinates (JSM) ---------------------------------------Another Jupiter centered cartesian coordinate system, JSM is the equivalent at Jupiter of GSM coordinates system at Earth. In this coordinate system, the X-axis points from Jupiter to the Sun. The secondary vector defining this coordinate system is the centered magnetic dipole axis (M) which is defined to be tilted 9.6 degrees from the Jovian spin axis towards 202 degrees SYS3 west longitude. The X-Z plane is contains M. Y completes the right handed set. The Y-Z plane rocks at the Jovian spin period about the Sun-Jupiter line. Local Hour ---------Local hour angle is the angle (HA) between the observer's (Galileo) sub-Jupiter meridian and the anti-sunward meridian, measured in the Jovian equatorial plane in the direction of planetary rotation. Local hour is the conversion of the local hour angle into units of decimal hours using the conversion factor of one hour to fifteen degrees of longitude. The following diagram is a graphic representation of local hour. Sun ^ | noon Planetocentric 12:00 Equatorial Projection | | | | Jupiter * * */ * | * (dusk) 18:00 -----------*--|--*------------- 06:00 (dawn) * | * * * * | | | |-HA-- 00:00 + Spacecraft midnight Magnetic Local Hour ------------------Magnetic local hour angle is the angle (MHA) between the observer's dipole meridian and the anti-sunward meridian, measured in the magnetic equatorial plane in the direction of planetary rotation. Magnetic local hour is the conversion of the magnetic local hour angle into units of decimal hours by using the conversion factor that equates one hour to fifteen degrees of longitude. The following diagram is a graphic representation of magnetic local hour. Sun ^ | noon Dipole 12:00 Equatorial Projection | | | | Jupiter * * */ * | * (dusk) 18:00 -----------*--|--*------------- 06:00 (dawn) * | * * * * | | | |-MHA- 00:00 + Spacecraft midnight Ancillary Data ============== There are several files that are provided in addition to the data files themselves that may be of value to the user. These include a detailed data gap listing (including reason for gap), a table of important spacecraft and instrument events, a discussion of instrument anomalies and resolutions, and a set of quick-look or 'browse' plots of the data. References ========== [DESSLER1983] Appendix B Coordinate Systems, in Physics of the Jovian Magnetosphere, ed. Dessler, Cambridge Univ. Press, New York, 1983. [KIVELSONETAL1992] The Galileo Magnetic Field Investigation, Space Science Rev. 60, 357, 1992. [KIVELSONETAL1996A] A Magnetic Signature at Io: Initial Report from the Galileo Magnetometer, Science, 273, 337, 1996 [KIVELSONETAL1996B] Io's interaction with the Plasma Torus, Science, 274, 396, 1996. [KIVELSONETAL1997A] Galileo at Jupiter: Changing states of the Magnetosphere and first looks at Io and Ganymede, Adv. Space Res., 20, No 2, 193, 1997. [HUDDLESTONETAL1998A] Location and Shape of the Jovian Magnetopause and Bowshock, J. Geophys. Res, 103, no. E9, 20075, 1998.

Alternate Names



  • Planetary Science: Fields and Particles

Additional Information



Questions and comments about this data collection can be directed to: Dr. Edwin V. Bell, II



NameRoleOriginal AffiliationE-mail
Dr. Margaret Galland KivelsonData ProviderUniversity of California, Los
Dr. Margaret Galland KivelsonGeneral ContactUniversity of California, Los
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