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Magnetometer Data

in the Mars Global Surveyor MAG/ER Level 1 Archive

Overview

The Magnetometer (MAG) vector magnetic field data reside in the directory DATA/MAG. These data were acquired by the Magnetometer instrument aboard the Mars Global Surveyor (MGS) spacecraft. The MAG data on this disk cover the period Aug. 26 - Sep. 17, 1998. The data files are in two subdirectories: one for data in planetocentric coordinates (PCENTRIC) and one for data in Sun-State coordinates (SUNSTATE). The files contain ASCII tables of time series data and are referred to as standard time series (STS) files.

The data are calibrated and are provided in physical units (nT). In addition, instrumental and spacecraft effects have been removed from the data during processing.

Each file consists of an attached ASCII text header, followed by an ASCII table containing the time series data. The table in each file has fixed-length records of length 232 bytes. Each row of data contains 24 columns, and is terminated by the ASCII record delimiter characters carriage return and line feed.

MAG data are represented in the planetocentric (PC) and Sun-State (SS) coordinate systems. Data are housed in the subdirectories PCENTRIC or SUNSTATE according to which system they embody. In the SS coordinate system, the X-axis lies along the instantaneous Mars-Sun vector and is positive toward the Sun. The negative of Mars' velocity vector is a second (Y) reference vector, so the vector cross product of X and Y yields a Z vector parallel to the northward (upward) normal of the orbit plane of Mars. The PC coordinate system is body-fixed and rotates with the body (Mars) as it spins on its axis. In the PC system, the Z-axis lies along the body rotation axis and is positive in the direction of angular momentum. The X-axis lies in the equatorial plane of the body, perpendicular to Z and in the direction of the prime meridian as defined by the IAU. The Y axis completes the right-handed set.

Each file in SS or PC coordinates contains one day of data.

This disk also contains browse plots which summarize the MAG and other data.

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Documents

This disk contains documentation files which describe the datasets on the disk, the instruments from which the data came, and the Mars Global Surveyor spacecraft and mission. These files are found in the CATALOG and DOCUMENT directories.

The following files in CATALOG are of particular interest to MAG data users.

• The MAG dataset is described in the file MAG_DS.CAT.
• The Magnetometer instrument is described in the file MAG_INST.CAT.
• The Mars Global Surveyor spacecraft is described in the file MGS_HOST.CAT.
• The Mars Global Surveyor mission is described in the file MISSION.CAT.
• A list of people associated with or relevant to the Magnetometer and Electron Reflectometer experiments is given in PERSON.CAT.
• Lists of literature references relevant to the Magnetometer and Electron Reflectometer (including references cited in the other catalog files) are found in REF.CAT.

The DOCUMENT directory contains the Software Interface Specification document for the data, in HTML and Microsoft Word document formats. (An ASCII text version is included for the sake of completeness, but is not fully formatted.)

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File Formats

The files on this disk are in level 1 compliance with the ISO 9660 standard. The MAG data are provided as ASCII tables of time series data.

Each MAG data file has an attached header that contains text describing the file processing and structure. The content of the headers is described in MAG_DS.CAT.

What follows is a very brief summary of the format of the data in the MAG files. All of the data fields indicated here, including the calibration columns, are explained more fully in the PDS format file MAG_DATA.FMT found in the subdirectories; that file is both human-readable and machine-readable. Note that the data file headers do not conform to this format.

Here are three lines of data with headings added, as an example of this format. Due to space limitations, only the first nine columns are displayed; the rest of each line is indicated by three dots. (Note: these data may be displayed with spacing different from that of the actual data. Each data line ends with two ASCII record delimiter characters, carriage return and line feed.)

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Browse Files

In addition to the data files, this disk contains PostScript browse plots summarizing the magnetic field data on the disk. These plots are contained in the BROWSE directory. They are housed in two subdirectories, corresponding to two different kinds of plots: RMS and MAG Calibration. The RMS plots are 3-panel plots of magnetic field magnitude and of RMS values of components Bx and By (in sensor coordinates). The MAG Calibration plots pertain to the calibration of the Magnetometer instrument.

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Links to Data and Browse Files

The links in the table below can be used to navigate the MAG data files and browse files on this disk.

The file naming convention for these data files is illustrated by the following example. (The file mentioned here, from PCENTRIC, is only an example; there are many more such files on the disk.)

98238.STS is interpreted as

98 = year 1998
238 = day of year 238 (where Jan. 1 = day of year 001)
STS = "standard time series" format

98238.LBL is the name of the PDS label file which describes the data file 98238.STS. Such label files provide descriptive information in a format which is both human-readable and machine-readable.

The naming convention for RMS browse files is similar to that for the data files:

98238.PS is interpreted as

98 = year 1998
238 = day of year 238 (where Jan. 1 = day of year 001)
PS = PostScript file.

Note: To make full use of the .LBL files in the following table, you must have a MAG_DATA.FMT file, for the correct coordinate system, in the same directory as each .LBL file. Obtain these MAG_DATA.FMT files via these two links:

MAG_DATA.FMT (Planetocentric)        MAG_DATA.FMT (Sun-State)

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