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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 Sep. 12 - 21, 1999. 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 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.

sample UT

Time (UT) as year, day of year, hour, minute, second, and millisecond.

decimal day 

Time as decimal day of year. (0000 hours on Jan. 1 = decimal day 1.000)

mag_vector 

Array[3] giving B-field components in the order Bx, By, Bz.

range

Gain range of MAG instrument.

sc_pos_vector 

Array[3] giving location of spacecraft (x, y, z).

calibration columns 

15 more columns, relevant to understanding the Magnetometer calibration.

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.)

sample UT

decimal day

Bx

By

Bz

range

sc_pos x

sc_pos y

sc_pos z

...

1998 87 0 26 51 371

87.018650127

-1.119

-1.059

4.960

11.

-9018.001

2299.323

-10512.695

...

1998 87 0 26 54 371

87.018684850

0.083

-1.377

2.719

11.

-9018.060

2300.060

-10507.870

...

1998 87 0 26 57 371

87.018719572

1.146

1.021

-2.139

11.

-9018.118

2300.797

-10503.042

...

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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.

Return to link in Overview section

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Links to Data and Browse Files

The following links 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.)

99255.STS is interpreted as

99 = year 1999
255 = day of year 255 (where Jan. 1 = day of year 001)
STS = "standard time series" format

99255.LBL is the name of the PDS label file which describes the data file 99255.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:

99255.PS is interpreted as

99 = year 1999
255 = day of year 255 (where Jan. 1 = day of year 001)
PS = PostScript file.

Date

Data Files (Planetocentric)

Data Files (Sun-State)

Browse Files

 

File

Bytes

Re-
cords

File

Bytes

Re-
cords

 

09/12/99

99255.STS

25349190

109575

99255.STS

25349190

109575

99255.PS

09/13/99

99256.STS

25772358

111399

99256.STS

25772358

111399

99256.PS

09/14/99

99257.STS

26215942

113311

99257.STS

26215942

113311

99257.PS

09/15/99

99258.STS

25861446

111783

99258.STS

25861446

111783

99258.PS

09/16/99

99259.STS

26700822

115401

99259.STS

26700822

115401

99259.PS

09/17/99

99260.STS

26503622

114551

99260.STS

26503622

114551

99260.PS

09/18/99

99261.STS

26718918

115479

99261.STS

26718918

115479

99261.PS

09/19/99

99262.STS

26718918

115479

99262.STS

26718918

115479

99262.PS

09/20/99

99263.STS

26050758

112599

99263.STS

26050758

112599

99263.PS

09/21/99

99264.STS

26306886

113703

99264.STS

26306886

113703

99264.PS

 

Return to point before data table

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