PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT PUBLICATION_DATE = 2001-07-12 NOTE = "INFO.TXT describes the Magnetometer (MAG) data available on this volume." END_OBJECT = TEXT END The DATA/MAG directory contains the Magnetometer (MAG) vector magnetic field data. These data were acquired by the Magnetometer instrument aboard the Mars Global Surveyor (MGS) spacecraft. The MAG data on this disk cover the period 6/29/98 - 7/27/98. The MAG data are provided at a variable time resolution, depending on the available telemetry rate, for the time period between Mars Orbit Insertion (MOI, 1997-09-12) and the beginning of the prime mission mapping (1999-03-31). 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 MAG data 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. 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 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 coordinates contains either one day of data or the data near a single periapsis of the spacecraft. Each file in PC coordinates contains data near a single periapsis. The MAG data files reside in the following subdirectories of DATA/MAG: SUNSTATE MAG data expressed in Sun-State coordinates. PCENTRIC MAG data expressed in planetocentric coordinates. The file naming convention for files in these subdirectories is as follows: 98087.STS is interpreted as 98 = year 1998 087 = day of year 087 (where Jan. 1 = day of year 001) STS = 'standard time series' format The detached PDS label file describing the file 98087.STS is named 98087.LBL. In addition to the data files, 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, and are described in the files CATALOG/CATINFO.TXT and DOCUMENT/DOCINFO.TXT. This disk also contains browse plots (PostScript files) pertaining to MAG data on the disk. These plots are contained in a subdirectory of the BROWSE directory. In addition to accessing MAG data files directly, users with Web browsers can access them via links in the HTML file MAGDATA.HTM in the EXTRAS directory. Such users also can navigate the entire disk using the file AAREADME.HTM in the disk root directory.