NSSDCA ID: PSFP-00261
Availability: At NSSDC, Ready for Offline Distribution (or Staging if Digital)
Time span: 1999-03-08 to 2005-04-26
This data set contains level 1 vector magnetic field and electron data acquired by the Magnetometer / Electron Reflectometer (MAG/ER) instrument aboard the Mars Global Surveyor (MGS) spacecraft. The data are provided at a variable time resolution depending on the telemetry rate available to the investigation for the time period beginning with the prime mission mapping (1999-03-08). The data were collected during the Mapping and Extended phases of the mission and expressed in Sun-State and Planetocentric coordinates.
The magnetometer data are calibrated and provided in physical units (nT). In addition, instrumental and spacecraft effects have been removed from the data during processing. Processed data in physical units from the Magnetometer are provided at full word downlink sampling resolution. The data are provided in several geophysical coordinate systems in order to make them directly usable for many analysis problems.
The instrument samples the magnetic field at a rate of 32 samples per second. Raw samples are averaged in the instrument according to the telemetry mode for the spacecraft and the data allocation for the MAG/ER investigation. A primary MAG full word sample consists of a 12 bit value for the x component, a 12 bit sample for the y component, a 12 bit sample for the z component (all in sensor coordinates) and a 4 bit range word (bit one is an autorange/manual range switch; bits 2,3,4 are the 0-7 range designation). This archive consists of outboard full word samples, which occur every 0.75s, 1.5s, or 3.0s, depending on the telemetry allocation.
The Electron Reflectometer Data Record (ERDR) is a time ordered series of electron measurements from the Mars Global Surveyor (MGS) Mission provided at full downlink sampling resolution. Each record consists of a time tag with 19 scalar data points representing measurements of the electron flux in 19 different energy channels, ranging from 10 eV to 20 keV, with an energy resolution of 25%. Each data point is a measure of the electron flux (cm-2 sec-1 ster-1 eV-1) averaged over a 360 x 14 degree disk-shaped field of view (FOV).
The ER data are organized into "packets", each of which contains 12, 24, or 48 seconds of data, respectively, for high, medium, and low spacecraft telemetry rates. Each packet is further subdivided into samples. The ER data set is generated at the rate of 6 samples per packet. When there are fewer than 6 samples per packet at a particular energy, data values are repeated in order to maintain a uniform table. The time listed for each record is the center of the sampling interval. When records are repeated, taking an average of the times for all repeated records provides the center time for that sample.
The ERDR is intended to be used in conjunction with MGS Magnetometer data records, which provide the magnetic field vector and spacecraft ephemeris data as a function of time. Electrons travel along the magnetic field lines in tight helices (few km radius) at high speed (roughly one Mars diameter per second). Thus the electron data contain information about the plasma environment as well as the large-scale configuration of the magnetic field, which is sampled locally by the MAG.
The MGS MAG/ER Level 1 archive volume set contains two distinct sequences of disks, each with a different naming convention for its members. The sequence MGSM_1xxx (starting with MGSM_1001) contains premapping data, while the sequence MGSM_2xxx (starting with MGSM_2001) contains mapping phase data. This difference in volume names reflects the significant differences between mapping and premapping phases (for example, the orbits during the mapping phase are nearly circular while orbits in the premapping period can be strongly elliptical).
The DVD Volume numbers start at DMSGM_2001 and the directories start at MGSM_2001. These are PDS data sets MGS-M-MAG-3-MAP1/FULLWORD-RES-MAG-V1.0 and MGS-M-ER-3-MAP1/OMNIDIR-FLUX-V1.0. These data are available online at:
Questions and comments about this data collection can be directed to: Dr. David R. Williams
Name | Role | Original Affiliation | |
---|---|---|---|
Dr. Raymond J. Walker | Data Provider | University of California, Los Angeles | rwalker@igpp.ucla.edu |
Dr. John E. P. Connerney | General Contact | NASA Goddard Space Flight Center | jec@lepjec.gsfc.nasa.gov |