PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM SPACECRAFT_NAME = MAGELLAN TARGET_NAME = VENUS OBJECT = TEXT PUBLICATION_DATE = 1997-08-01 NOTE = "MAGELLAN SPHERICAL HARMONIC MODELS AND DIGITAL MAPS ARCHIVE" END_OBJECT = TEXT END MAGELLAN SPHERICAL HARMONIC MODELS AND DIGITAL MAPS ARCHIVE 1. Introduction This archive contains Magellan spherical harmonic models of the Venusian gravity and topography field, and digital maps of the bouguer anomalies, free-air gravity accelerations and errors, geoid anomalies and errors, and topography. It also contains documentation which describes the products. The spherical harmonic products and the digital maps in this archive are the exact products released by the Magellan Project. Supporting documentation and label files conform to the Planetary Data System (PDS) Standards, Version 3.0, Jet Propulsion Laboratory (JPL) document JPL D-7669. Additional information about the Magellan gravity experiment, including the acquisition, processing, and quality of the data, can be found in Konopliv, A.S. and Sjogren, W.L., Venus Gravity Handbook, JPL Document 96-2. This document is available from the Planetary Data System (PDS) Geosciences Node, Washington University, St. Louis, MO. 63130. More Magellan gravity data and documents are available via the internet through the PDS Geophysics Subnode World Wide Web site: http://pds-geophys.wustl.edu/pds/magellan 2. File Formats The data files are in three formats: array, image, and tabular. The array formats are 2-dimensional ASCII global grids of 180 lines by 360 samples (i.e. 1 degree resolution). These files are described by detached PDS labels. There are images of each of the gridded ASCII data files. Each image is 180 lines by 360 samples, with one byte per sample. The images are described by detached PDS labels. There are also binary digital map images of the bouguer anomalies, free-air gravity accelerations and errors, geoid anomalies and errors, and topography. These digital maps are described by attached PDS labels. Tabular files are formatted so that they may be read directly into many software analysis systems on various computers. All fields are separated by commas, and character fields are enclosed in double quotation marks ("). Character fields are left justified, and numeric fields are right justified. The "start byte" and "bytes" values listed in the labels do not include the commas between fields or the quotation marks surrounding character fields. The records are of fixed length, and the last two bytes of each record contain the ASCII carriage return and line feed characters. This allows a table to be treated as a fixed length record file on computers that support this file type and as a normal text file on other computers. Tabular files are described by PDS detached or attached labels. All document files and detached label files contain stream format records, with a carriage return character (ASCII 13) and a line feed character (ASCII 10) at the end of each line. This allows the files to be read by the MacOS, DOS, Unix, and VMS operating systems. The detached PDS label file has the same name as the data file it describes, with the extension .LBL; for example, the file BOUGGRD.DAT is accompanied by the detached label file BOUGGRD.LBL in the same directory. PDS labels are object-oriented. The object to which the label refers (e.g., IMAGE, TABLE, etc.) is denoted by a statement of the form: ^object = location in which the carat character (^, also called a pointer in this context) indicates that the object starts at the given location. In an embedded label, the location is an integer representing the starting record number of the object (the first record in the file is record 1). In a detached label, the location denotes the name of the file containing the object, along with the starting record or byte number. For example: ^IMAGE = "BOUGGRD.IMG" indicates that the IMAGE object points to the file BOUGGRD.IMG, in the same directory as the detached label file. Below is a list of the possible formats for the ^object keyword. ^object = n ^object = n ^object = "filename.ext" ^object = ("filename.ext",n) ^object = ("filename.ext",n) where n is the starting record or byte number of the object, counting from the beginning of the file (record 1, byte 1) indicates that the number given is in units of bytes filename is the upper-case file name ext is the upper-case file extension 3. Archive Contents The files in this archive are organized in one top-level directory with several subdirectories. The following diagram shows the structure and content of these directories. In the diagram, directory names are enclosed in square brackets ([]), upper-case letters indicate an actual directory or file name, and lower-case letters indicate the general form of a set of directory or file names. FILE CONTENTS Top-level directory | |- AAREADME.TXT The file you are reading. | |- VOLDESC.CAT A description of the archive contents. | |- [CATALOG] A directory containing PDS catalog files, | | and information about the datasets. | | | |- CATINFO.TXT Description of files in the CATALOG | | directory. | | | |- DSMP.CAT A description of the simple cylindrical | | map projection. | | | |- MISSION.CAT A brief description of the mission. It | | includes a chronology of events, definition | | of mission phases, and science objectives. | | | |- INSTHOST.CAT A description of the Magellan spacecraft and | | an overview of the NASA Deep Space Network (DSN). | | | |- RSSINST.CAT An overview of the spacecraft radio science | | system on Magellan and a summary description of | | the Deep Space Network instrumentation which | | supports radio science experiments. | | | |- RDRSINST.CAT An overview of the spacecraft radar system | | on Magellan. | | | |- GRAVDS.CAT PDS dataset catalog file. A description | | of the spherical harmonic gravity model | | and digital gravity map dataset, including | | parameters, processing, data coverage | | and quality. | | | |- TOPODS.CAT PDS dataset catalog file. A description | | of the spherical harmonic topography model | | and digital topography map dataset, including | | parameters, processing, data coverage | | and quality. | | | |- REF.CAT A listing of references used elsewhere in | | the streamlined catalog files and of references | | that might be generally useful in working | | with these data. | | | |- PERSON.CAT A listing of key people involved in | generating and processing the archival dataset. | |- [DOCUMENT] A directory containing document files | | relating to this archive. | | | |- DOCINFO.TXT Description of files in the DOCUMENT | | directory. | | | |- SHADR.TXT. The SIS document describing the format and | | content of the spherical harmonic data files. | | | |- RSDMAP.TXT The SIS document describing the format and | content of the radio science digital map files. | |- [GRAVITY] A directory containing a spherical | | harmonic model of the gravity field, | | binary digital gravity map files, | | ASCII data files and PDS detached labels. | | | |- SHG120.TAB A 120-th degree and order spherical | | harmonic model of the gravity field. | | | |- BOUGUER.DAT A digital map of bouguer gravity anomalies. | | | |- BOUGGRD.DAT A 180 line by 360 sample ASCII array of | | bouguer gravity anomalies. | | | |- BOUGGRD.LBL A PDS detached label describing | | BOUGGRD.DAT. | | | |- FREEAIR.DAT Digital maps of the free-air gravity | | accelerations and associated errors. | | | |- FAIRGRD.DAT A 180 line by 360 sample ASCII array of | | free-air gravity accelerations. | | | |- FAIRGRD.LBL A PDS detached label describing | | FAIRGRD.DAT. | | | |- FAIRERR.DAT A 180 line by 360 sample ASCII array of | | the errors in the the free-air gravity | | accelerations. | | | |- FAIRERR.LBL A PDS detached label describing | | FAIRERR.DAT. | | | |- GEOID.DAT Digital maps of the geoid anomalies | | and associated errors. | | | |- GEOIDGRD.DAT A 180 line by 360 sample ASCII array of | | geoid anomlies. | | | |- GEOIDGRD.LBL A PDS detached label describing | | GEOIDGRD.DAT. | | | |- GEOIDERR.DAT A 180 line by 360 sample ASCII array of | | the errors in the geoid anomalies. | | | |- GEOIDERR.LBL A PDS detached label describing | GEOIDERR.DAT. | |- [IMAGES] A directory containing byte-scaled images | | of the ASCII data files in the GRAVITY and | | TOPO directories. | | | |- BOUGGRD.IMG A 180 line by 360 sample byte-scaled | | image of bouguer gravity anomalies. | | | |- BOUGGRD.LBL A PDS detached label describing | | BOUGGRD.IMG. | | | |- FAIRGRD.IMG A 180 line by 360 sample byte-scaled | | image of free-air gravity accelerations. | | | |- FAIRGRD.LBL A PDS detached label describing | | FAIRGRD.IMG. | | | |- FAIRERR.IMG A 180 line by 360 sample byte-scaled | | image of the errors associated with the | | free-air gravity accelerations. | | | |- FAIRERR.LBL A PDS detached label describing | | FAIRERR.IMG. | | | |- GEOIDGRD.IMG A 180 line by 360 sample byte-scaled | | image of geoid anomalies. | | | |- GEOIDGRD.LBL A PDS detached label describing | | GEOIDGRD.IMG. | | | |- GEOIDERR.IMG A 180 line by 360 sample byte-scaled | | image of the errors associated with | | the geoid anomalies. | | | |- GEOIDERR.LBL A PDS detached label describing | | GEOIDERR.IMG. | | | |- TOPOGRD.IMG A 180 line by 360 sample byte-scaled | | image of topography. | | | |- TOPOGRD.LBL A PDS detached label describing | TOPOGRD.IMG. | |- [TOPO] A directory containing a spherical | harmonic model of the topography field, | a binary digital topography map file, | an ASCII data file and PDS detached label. | |- SHT360.TAB A 360-th degree and order spherical | harmonic model of the topography field. | |- TOPO.DAT A digital map of topography. | |- TOPOGRD.DAT A 180 line by 360 sample ASCII array of | topography. | |- TOPOGRD.LBL A PDS detached label describing TOPOGRD.DAT. 4. Ancillary Data A useful product for understanding the errors in the gravity solution is the gravity field covariance matrix. The gravity field covariance represents the complete error description for the SHG120 gravity field solution, including the coefficient variances (sigmas^2), and the correlations between all the coefficients. It is a product of the least squares solution that derived SHG120. The covariance provides a more complete description of the error associated with the SHG120 gravity field solution, than would be available from the sigmas alone. The covariance matrix is large (~857 MB) since it contains the correlations of each of the solution parameters with all the other parameters. (SHG120 solved for 14756 spherical harmonic coefficients, and the Venusian GM value). The full covariance matrix was used to compute the error maps for the gravity anomalies, and geoid anomalies that are associated with this archive. The covariance matrix is available on request from the PDS Geoscience Node (contact Jim Alexopoulos at 314-935-5365 or jim@wuzzy.wustl.edu) or from JPL (contact Alex Konopliv at 818-354-6105 or ask@krait.jpl.nasa.gov). 5. Whom to Contact for Information For questions concerning this archive, data products, associated PDS labels and documentation: Jim Alexopoulos Washington University Dept. of Earth and Planetary Sciences 1 Brookings Drive Campus Box 1169 St. Louis, MO 63130 314-935-5365 jim@wuzzy.wustl.edu For questions concerning the generation of the spherical harmonic gravity model and digital gravity map products: William L. Sjogren Magellan Gravity Principal Investigator Jet Propulsion Laboratory California Institute of Technology 4800 Oak Grove Drive MS 301-150 Pasadena, CA 91109 818-354-4868 wls@kamel.jpl.nasa.gov Alex S. Konopliv Jet Propulsion Laboratory California Institute of Technology 4800 Oak Grove Drive MS 301-125J Pasadena, CA 91109 818-354-6105 ask@krait.jpl.nasa.gov For questions concerning the generation of the spherical harmonic topography model and digital topography map product: Nicole J. Rappaport Jet Propulsion Laboratory California Institute of Technology 4800 Oak Grove Drive MS 301-125L Pasadena, CA 91109 818-393-6388 njb@nomad.jpl.nasa.gov For questions concerning the gravity data: William L. Sjogren Jet Propulsion Laboratory Pasadena, CA Dr. Roger J. Phillips Washington University Dept. of Earth and Planetary Sciences 1 Brookings Dr. Campus Box 1169 St. Louis, MO 63130 314-935-6356 phillips@wustite.wustl.edu This archive was produced by Jim Alexopoulos.