MGN RDRS Global Emissivity Data Record (GEDR)

GEDR – Global Emissivity Data Record

PDS3 Data Set ID: MGN-V-RDRS-5-GDR-EMISSIVITY-V1.0 (DOI: 10.17189/1522530) (for first mapping cycle products, go here)

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

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

The Radar System (RDRS) Global Emissivity Data Record (GEDR) consist of mosaics of the emissivity of the Venusian surface in four projections: mercator equatorial (MERC), sinusoidal equal area equatorial SINUS), north polar (NORTH), and south polar (SOUTH).

The emissivity of a surface is defined as the thermal power emitted by that surface divided by the power emitted by a black body of the same size and at the same physical temperature. The polarization direction is horizontal (E-field tangential to surface), and the emissivity is not corrected for emission angle or surface roughness or tilt.

To make the GEDR images, Magellan radiometer data, in the form of readings of antenna noise temperature, are corrected for antenna sidelobe effects and for emission and absorption by the Venus atmosphere. The component reflected from the surface is modeled as a specular reflection with power reflection coefficient equal to (1-emissivity). The location and planetary radius at the antenna boresight intercept point are derived from Global Topographic Data Record (GTDR) images and the physical surface temperature is calculated using an adiabatic model. The data are then filtered to remove low-frequency instrument calibration errors, and re-sampled into sinusoidal, Mercator, and north and south polar stereographic projections at a resolution of about 5 x 5 kilometers per pixel.

In ODE, GEDR products have the following product IDs:

gedr_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.