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Magnetometer Data

in the NEAR Magnetometer Processed Data Archive

Overview

The Magnetometer (MAG) vector magnetic field data reside in the subdirectories of the directory DATA/MAG. These data were acquired by the Magnetometer instrument aboard the Near Earth Asteroid Rendezvous (NEAR) spacecraft. The MAG data on this disk cover the period Jan. 27 - Dec. 22, 1998. The data files belonging to the mission phase of the disk are collected into subdirectories according to the dates of the data that they contain. For example, the directory 1998_020 would contain data collected in 1998 on days 020 - 029. The data files themselves have the file extension TAB. Each data file is an ASCII table containing time tags, magnetic field component and magnitude values, and spacecraft position values.

Data are provided in two coordinate systems: Eros Body Fixed (EBF) and NEAR Sun Orbital (NSO) coordinates. Files with names beginning with EBF contain data in EBF coordinates, while files with names beginning with NSO contain data expressed in NSO coordinates. These coordinate systems are described in the text of the label files (*.LBL) associated with the data files (*.TAB).

The data are calibrated and processed, and are provided in physical units (nT). In addition, instrumental and spacecraft effects have been removed from the data during processing. The data are described in detail in the files CATALOG/MAGL2DS.CAT and AAREADME.TXT on this disk. (A web page version of AAREADME.TXT is found in AAREADME.HTM.)

Each file consists of an ASCII table containing data for one day. The table in each file has fixed-length records of length 124 bytes. Each row of data contains 13 columns, and is terminated by the ASCII record delimiter characters carriage return and line feed.

This disk also contains browse plots which summarize the MAG 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 NEAR 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 MAGL2DS.CAT.
• The Magnetometer instrument is described in the file MAGINST.CAT.
• The NEAR spacecraft is described in the file INSTHOST.CAT.
• The NEAR mission is described in the file MISSION.CAT.
• A list of people associated with or relevant to the Magnetometer experiment is given in PERSON.CAT.
• Lists of literature references relevant to the Magnetometer (including references cited in other catalog files) are found in REF.CAT.

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Browse Files

In addition to the data files, this disk contains browse plots in PDF format, summarizing the magnetic field data on the disk. These plots are contained in the EBF and NSO subdirectories of the BROWSE directory. Another set of browse files summarizing the data, in JPEG format, are in the PROJECT subdirectory of BROWSE, and can be accessed through the file INDEX.HTM file there.

This disk also contains Splash files for the data. These files can be used in conjunction with the Splash software to produce customized plots of the data. The Splash software and files are contained in the EXTRAS/SPLASH directory. Once a Splash plot is opened using the Splash program, the user can click on various features of the plot to open dialog boxes which can be used to view and change the features of the plot. Please note that the Splash software runs only on Windows platforms.

Each PDF or Splash plot consists of a set of graphical panels, arranged vertically, together with a set of variable values at the bottom of the page. Each plot has four panels corresponding to the components of the magnetic field (X, Y, and Z) and the total magnetic field. Each EBF plot also has a fifth panel showing spacecraft position (X, Y and Z coordinates). The panels show plots of these quantities vs. time. At the bottom of each plot is a display of values of spacecraft position corresponding to times indicated on the panels. Units for the data in the plot are nT for magnetic field and km for space coordinates. Coordinates for the data in the plot are EBF or NSO, as indicated by the filename. The plots have been scaled so as to cut off most data spikes due to spacecraft propulsion events and similar sources of error.

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Links to Data and Browse Files

The following links can be used to navigate the MAG data files, PDF browse files, and Splash files on this disk.

The file naming convention for these data files is illustrated by the following example.

EBF98027.TAB is interpreted as:

EBF = coordinate system of the data
98 = year 1998
027 = day of year 027 (where Jan. 1 = day of year 001)
TAB = table format

EBF98027.LBL is the name of the PDS label file which describes the data file EBF98027.TAB. Such label files provide descriptive information in a format which is both human-readable and machine-readable.

The file naming convention for PDF browse files is similar to the one for data files, except that the file names have PDF extensions. Thus, for example, the browse plot EBF98027.PDF is based on the data in file EBF98027.TAB. The Splash files have a similar naming convention, but with file extension SPH instead of PDF.

CAUTION: The links to PDF and Splash file links will not work properly if software for viewing these files is not available on your system. Do not click the PDF links unless you have a program capable of reading PDF files (such as Adobe Acrobat Reader) installed on your system and have assigned the file extension PDF to that program. Do not click the Splash file links unless you have Splash installed on your system and have assigned the file extension SPH to Splash. Please note that Splash can be installed only on Windows platforms.

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