PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT INTERCHANGE_FORMAT = ASCII PUBLICATION_DATE = 1994-05-13 NOTE = "Brief text description of Magellan GVDR." END_OBJECT = TEXT END Volume GVDR_0001 Magellan Project Global Vector Data Record (GVDR) AAREADME.TXT 11 May 1994 R.A. Simpson Stanford University ==================================================================== INTRODUCTION ==================================================================== This compact disc contains archival data produced during the Magellan Mission. This collection of data is intended to be the best quantitative description of the electrical properties of the Venusian surface that can be derived at 18 km resolution from the Magellan data set. The disc contains tabulated data for pixels organized in four separate projections. The projections are north polar stereographic, south polar stereographic, sinusoidal equal area (equatorial), and Mercator (equatorial). For each projection the tabulated data give results from four separate analyses: MIT ARCDR results for planetary radius, rms surface roughness, and reflectivity from nadir altimetry; Stanford SCVDR results for near-nadir backscatter function from altimetry; MIT ARCDR results for emissivity from passive radiometry measurements; and Stanford SCVDR estimates of the oblique backscatter function from analysis of SAR image data. The ARCDR is the Altimetry and Radiometry Composite Data Record; the SCVDR is the Surface Characteristics Vector Data Record. Discs in the volume set have the following coverage: VOLUME_ID Version Data Type Coverage --------- ------- --------- --------------- GVDR_0001 1 ARCDR Orbits 376-5747 SCVDR Orbits 376-2599 ==================================================================== VOLUME SET INFORMATION ==================================================================== This disc is the first of at least two which contain data from global gridding of Magellan scattering and radiometry data. Each archive volume will have the structure illustrated in the diagram below. root | |- AAREADME.TXT |- ERRATA.TXT |- VOLDESC.CAT | |- CATALOG | | | |- CATINFO.TXT Streamlined PDS templates | |- MISSION.CAT for mission, host, | |- SC_HOST.CAT instrument, reference, | |- RDRSINST.CAT personnel, and data set. | |- REFS.CAT Also, object definitions | |- PERSONEL.CAT for data set and individual | |- GVDR_DS.CAT map projections. | |- IMPNORTH.LBL | |- IMPSOUTH.LBL | |- IMPSINU.LBL | |- IMPMERC.LBL | |- DSMP.LBL | |- DOCUMENT | | | |- DOCINFO.TXT | |- GVDRSIS.TXT GVDR SIS | |- TILING.TXT | |- INDEX | | | |- INDXINFO.TXT | |- INDEX.LBL | |- INDEX.TAB | |- CUMINDEX.LBL | |- CUMINDEX.TAB | |- SOFTWARE | | | |- SOFTINFO.TXT | |- SOURCE | |- SUN4 | |- DECMIPS | |- GVDR Data directories; subdirectories | contain tables of scattering and |- SINU emissivity results for use with |- MERC pixels defined in four separate |- NORTH projections. |- SOUTH ==================================================================== ERRATA ==================================================================== A cumulative list of errors and changes is maintained in the file ERRATA.TXT at the root level of each volume. Higher volume numbers will show errors in this disc discovered after it was produced. ==================================================================== DISC FORMAT ==================================================================== The disc is organized according to the PDS standard for "one data set, one volume." This file (AAREADME.TXT), a PDS volume object definition (VOLDESC.CAT), and the listing of errors and changes (ERRATA.TXT) are included at the root level. The following directories of descriptive material are also at the root level: CATALOG contains descriptive files for cataloging each of the data types included in this disc. DOCUMENT contains a plain text Software Interface Specification (SIS) for the GVDR. INDEX contains index information on each of the data files included in this disc; it also includes a cumulative index to all files in this volume set. SOFTWARE contains source code and executables for use with the data on this disc. The remaining directories at the root level contain data files and detached PDS labels. ==================================================================== FILE FORMAT ==================================================================== All data files on the disc are accompanied by detached PDS labels, which describe their contents. PDS TEXT objects include attached labels. PDS labels do not include an SFDU label. Labels have the same file name as the primary data file but have a suffix ".LBL" appended. In many cases, the structure of the file has been abstracted from the ".LBL" file and is included in a separate file of the same name but with an extension ".FMT". The Software Interface Specification (SIS) for the GVDR is included in the DOCUMENT directory. In most cases, however, the detailed information on the structure and the contents of data files is contained in the ".LBL" and ".FMT" files, examples of which are included as appendices to the GVDR SIS. Text files, are delimited with carriage-return (ASCII 13) line- feed (ASCII 10) pairs at the end of each line. Files intended for immediate use with computers (source code, Unix-style Makefiles, binary executables, and files of compressed software) in the SOFTWARE directory do not have PDS labels. No do these files have special line delimiters (no carriage-return line- feed pairs, for example). ==================================================================== DATA FILE CONTENTS ==================================================================== Data files are stored in subdirectories under the GVDR directory. Each subdirectory contains data for one map projection (SINU for sinusoidal equal area, MERC for Mercator, NORTH for north polar stereographic, and SOUTH for south polar stereographic). Each projection subdirectory has four types of data files: ADF, altimetry analysis results from the ARCDR; ANF, altimetry inversions from the SCVDR; RDF, radiometry analysis results from the ARCDR; and XIF, SAR image analysis results from the SCVDR. Several other files can also be found in each projection subdirectory, including a variation on the GEO.TAB file found on other Magellan products; a GVDR header file; and files giving pointers to both tiles and pixels. To locate data in the GVDR, the user should first locate the tile which contains the region of interest. The tile index table will then give pointers into the four data tables for the beginning of the tile. The pixel index table will then give pointers into the four data tables for the beginning of pixel information relative to the beginning of the tile. The number of entries in the data tables can vary from pixel to pixel; the pixel index table also indicates how many entries apply for each pixel. The GVADF data table includes the following: the number of ARCDR footprints included, the mean radius and its variance, the mean rms slope and its variance, and the mean Fresnel reflectivity and its variance (without correction for diffuse scattering). The GVANF data table includes the following: the number of SCVDR footprints included; the Doppler centroid of the echo; the angle of the nadir track on the Venusian surface; the number of points in the derived nadir backscatter function; the derived backscatter function and its variance; and results from fitting the derived backscatter function to Hagfors, Muhleman, gaussian, exponential, and Rayleigh functions. The GVRDF data table includes the following: the number of ARCDR footprints included; the azimuth and incidence angles at the surface point; the polarization angle at the spacecraft; and the emissivity and its variance. The GVXIF data table includes the following: the number of image framelets used to compute the oblique scattering surface properties; the azimuth and incidence angles at the target location; the polarization angle at the spacecraft; the pixel histogram median, mode, upper knee, and lower knee; and three coefficients to a polynomial fitted to the oblique backscatter data. ==================================================================== ACKNOWLEDGMENTS ==================================================================== Assistance in developing PDS formats for data was provided initially by Margaret Cribbs, Gail Woodward, and Sue Hess of the Planetary Data System. Ron Joyner provided much of the late guidance and review. Suggestions and assistance at various stages of both the SCVDR and GVDR production was provided by Peter Ford. ==================================================================== DISCLAIMER ==================================================================== Although considerable care has gone into making this volume set, errors are both possible and likely. Users of the data are advised to exercise the same caution as they would when dealing with any other unknown data set. Reports of errors or difficulties would be appreciated. Please contact one of the persons listed below. ==================================================================== COGNIZANT PERSONEL ==================================================================== The persons most directly responsible for construction and release of this volume set are Michael J. Maurer and Richard A. Simpson. Although many people contributed to the volume set, any faults in the product are theirs alone. The Magellan Investigator for this work was G. Leonard Tyler. Michael J. Maurer 415-723-1024 maurer@nova.stanford.edu Richard A. Simpson 415-723-3525 rsimpson@magellan.stanford.edu G. Leonard Tyler 415-723-3535 len@nova.stanford.edu All at: Center for Radar Astronomy Durand Bldg - Room 232 Stanford University Stanford, CA 94305-4055