MGN RDRS Global Vector Data Record (GVDR)

GVDR – Global Vector Data Record

PDS3 Data Set ID: MGN-V-RDRS-5-GVDR-V1.0 DOI: 10.17189/1522512

PDS4 Bundle:urn:nasa:pds:magellan_gvdr DOI: 10.17189/b4v1-8n72

For more information about RDRS GVDR products, see the GVDR Data Set Description.

The Radar System (RDRS) Global Vector Data Record (GVDR) is a sorted collection of scattering and emission measurements from the Magellan Mission. The sorting is into a grid of equal area “pixels” distributed regularly about the planet. For data acquired from the same pixel but in different observing geometries, there is a second level of sorting to accommodate the different geometrical conditions. The “pixel” dimension is 18.225 km. The GVDR is presented in four projections: mercator equatorial (MERC), sinusoidal equal area equatorial (SINU), north polar (NORTH), and south polar (SOUTH).

The GVDR is intended to be the most systematic and comprehensive representation of the electromagnetic properties of the Venus surface that can be derived from Magellan data at this resolution. It should be useful in characterizing and comparing distinguishable surface units.

The Magellan data set comprises three basic data types: echoes from the nadir-viewing altimeter (ALT), echoes from the oblique backscatter synthetic aperture radar (SAR) imaging system, and passive radiothermal emission measurements made using the SAR equipment. The objective in compiling the GVDR is to obtain an accurate estimate of the surface backscatter function (or “sigma-zero”) for Venus from these three data types and to show its variation with incidence (polar) angle, azimuthal angle, and surface location.

The GVDR data set comprises several “tables” of results based on analysis of each of the data types described above. These include:

Data Table	Description
Image	Contains results from analysis of SAR image strips. The results are parameterized by the azimuth angle, the incidence (polar) angle, and the polarization angle. Quantities include the number of image framelets used to compute the scattering parameters; the median, the mode, and the one-standard deviation limits of the pixel histogram; and the three coefficients and the reference angle of the quadratic approximation to sigma-zero as a function of incidence angle.
Radiometry	Contains results from Massachusetts Institute of Technology (MIT) analysis of the radiometry data. The results are parameterized by the azimuth angle, the incidence angle, and the polarization angle. The results include the number of radiometry footprints used to compute the estimate of thermal emissivity, the emissivity, and its variance.
MIT ALT	Contains results derived from the MIT altimetry data analysis. The results include the number of Altimeter and Radiometry Composite Data Records (ARCDRs) Altimetry Data File (ADF) footprints used in computing the estimates of scattering properties for the pixel and estimates (and variances) of radius, RMS surface tilt, and Fresnel reflectivity from the ARCDR.
Stanford ALT	Contains results from the Stanford analysis of altimetry data. Results include the number of Surface Characteristics Vector Data Record (SCVDR) footprints used in computing the estimates of surface properties for this pixel, the centroid of the Doppler spectrum, the derived scattering function and the angles over which it is valid, variance of the individual points in the derived scattering function, and results of fitting analytic functions to the derived scattering function.

In ODE, GVDR products, which include the files in the table below, have the following product IDs:

GVXXX_YYYYY

where:

yyyyy = map projection (MERC, SINUS, NORTH, SOUTH, or ERROR)

Within the GVDR product directory, there are four subdirectories divided by map projection. Within each of these subdirectories, the following files types appear as a data file (.TAB), a structure file (.FMT), a PDS3 label file (.LBL) and a PDS4 label file (.XML).

File Name	Data File Content
GVHDR	Summary information for data in this GVDR projection.
GVTIDX	Tile index, containing coarse (tile) pointers to actual data in other .TAB files.
GVPIDX	Pixel index, containing fine (pixel-level) pointers to actual data in other .TAB files.
GVADF	Radius and estimates of surface properties (reflectivity and RMS roughness) from template fitting to Hagfors functions at MIT (ARCDR) data.
GVANF*	Estimates of surface properties from Stanford linear inversion. Includes experimentally derived specific radar cross section, and results of fits to those curves.
GVRDF	Thermal emissivity results from MIT radiometry analysis.
GVXIF	Measures of surface scatter at oblique angles from SAR image data. Also includes statistics on pixel values.
GVGEO	Coordinates for named geologic features. Comparable to GEO.TAB files on other Magellan archival products.
GVORB	Record of source files for data in this GVDR projection.
GVTGEOM	Latitude and longitude of GVDR tile corners.

*In addition to the GVANF.FMT structure file, this file type also has a GVNNF.FMT structure file.