MGN RDRS Global Topography Data Record (GTDR)

GTDR – Global Topography Data Record

PDS Data Set ID: MGN-V-RDRS-5-GDR-TOPOGRAPHIC-V1.0 (DOI: 10.17189/1522522Citations of DOI: 10.17189/1522522) (for first mapping cycle products, go here)

PDS4 Bundle:urn:nasa:pds:magellan_gxdrDOI: 10.17189/kv67-gt18

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

The Radar System (RDRS) Global Topography Data Record (GTDR) consists of topographic maps of Venus in four projections – mercator equatorial (MERC), sinusoidal equal area equatorial (SINUS), north polar (NORTH), and south polar (SOUTH) – and an error map (ERROR).

The range to surface is derived by fitting altimeter echoes from the fan-beam altimetry as a function of time to Hagfors’ radar backscatter model templates. The ranges are subtracted from the spacecraft radial coordinate (derived from Doppler tracking), yielding measurements of planetary radius. The data are filtered to remove low-frequency errors in the in-plane elements of each spacecraft orbit, and then re-sampled into sinusoidal, Mercator, and north and south polar stereographic projections at a resolution of about 5 x 5 kilometers per pixel.

A fifth image contains estimates of the absolute accuracy of the radius values in each pixel of the sinusoidal projection. This is derived by taking the root mean square of (a) the statistical accuracy anticipated from the template fitting and (b) the systematic errors estimated from the in-plane element filtration. Note that this is the absolute topographic accuracy. Relative errors are much smaller, about 10-15 meters in relatively flat areas.

In ODE, GTDR products have the following product IDs:

gtdr_yyyy

where:

yyyyy = map projection (merc, sinus, north, or south)

Within the data directory under the bundle root directory, there are four subdirectories divided by map projection. They are: "mercator" for the Mercator projection products, "sinusoidal" for the sinusoidal map projection products, "north" for the north polar stereographic products, and "south" for south polar stereographic products.

Each map product consists of three files. There are the image file (*.img), the ENVI header file (*.hdr) for use in reading the data into the commercial ENVI software package, and the PDS4 label (*.xml) that describes both the image file and ENVI header.