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Electron Reflectometer Data

in the Mars Global Surveyor MAG/ER Level 1 Archive

Overview

The Electron Reflectometer (ER) data reside in the directory DATA/ER. These data consist of a time ordered series of omnidirectional electron flux measurements from the Electron Reflectometer instrument on the Mars Global Surveyor (MGS) spacecraft. The ER data on this disk cover the period Jun. 24 - Jul. 18, 1998. The data files contain ASCII tables of time series data and hence are referred to as standard time series (STS) files.

Within a file, 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 about 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). (Parts of this FOV are masked because of spacecraft obstructions.) During the Science Phasing Orbits (SPO), the spacecraft was in Array Normal Spin (ANS) configuration, for which the ER field of view sweeps out the entire sky (4-pi ster) every 50 minutes, which is much longer than the integration time per record (2 to 48 sec, depending on energy and telemetry rate) and much longer than most timescales of interest in Mars' plasma environment. The ER data are intended to be used in conjunction with the Mars Global Surveyor Magnetometer (MAG) data, 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 about the large-scale configuration of the magnetic field, which is sampled locally by the MAG.

Each ER data file consists of an attached ASCII text header, followed by an ASCII table containing 1 day of time series data. The table in each file has fixed-length records of length 233 bytes. Each row of data contains 20 columns, and is terminated by the ASCII record delimiter characters carriage return and line feed. Each row consists of a time stamp followed by 19 electron flux values. The data are provided at the full instrument downlink sampling frequency, which varies by orbit (spacecraft telemetry mode).

In addition to data files, this disk also contains browse plots which summarize the ER 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 ER data users.

• The ER dataset is described in the file ER_DS.CAT.
• The ER instrument is described in the file ER_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 ER and MAG instruments is given in PERSON.CAT.
• A list of literature references relevant to the ER and MAG (including references cited in the other catalog files) is 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 ER data are provided as ASCII tables of time series data. Each file has an attached header that contains text describing the file processing and structure. The content of the headers is much like that of the Magnetometer data file headers (see MAG_DS.CAT).

What follows is a very brief summary of the format of the data in the ER files. This format also is described in the PDS format file ER_DATA.FMT found in the monthly subdirectories; this file is both human-readable and machine-readable. Note that the data file headers do not conform to this format.

Three lines of data with headings added, as an example of this format:

(Note: These data may be displayed with spacing different from that of the actual data. Data have been abbreviated in the middle as indicated. 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, and are explained in the INFO.TXT file in the BROWSE/MAG_CAL subdirectory.

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Links to Data and Browse Files

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

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

98175.STS is interpreted as

98 = year 1998
175 = day of year 175 (where Jan. 1 = day of year 001)
STS = "standard time series" format

98175.LBL is the name of the PDS label file which describes the data file 98175.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:

98175.PS is interpreted as

98 = year 1998
175 = day of year 175 (where Jan. 1 = day of year 001)
PS = PostScript file.

Note: To make full use of the .LBL files, you must have the ER_DATA.FMT file in the same directory as the .LBL files. Obtain ER_DATA.FMT via this link: ER_DATA.FMT

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