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1993-07-13
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MAGELLAN PROJECT OFFICE
MIT ID: GEDRP.1;2
JPL ID: P-40347
Date: 6/15/92
These images display the distribution of radio-thermal emission
efficiency (emissivity) over the Venus surface, observed using the
Magellan SAR radar receiver. Color is used to code the emission
efficiency (see color bar). Red corresponds to the highest, blue to the
lowest values of emissivity. The upper image shows that part of the
planet between 69 degrees north and 69 degrees south latitude in
Mercator projection; beneath it are the two polar regions covering
latitudes above 44 degrees in stereographic projection. Easterly
longitudes run across the Mercator map from left to right, and around
the periphery of the polar stereographic projections. The emissivity of
the surface is determined primarily by its bulk electrical properties
and on the angle at which the emitted radiation is viewed. The decrease
in average emissivity at low latitudes results from the higher view
angle there. The horizontal resolution also varies with latitude, being
determined solely by the "footprint" of Magellan's high-gain SAR antenna
beam.
Near the equator the surface resolution is about 20 kilometers, but at
high latitudes it degrades to as much as 100 kilometers.
There is a tendency for elevated regions, e.g. the Maxwell Montes (left
of the data gap at top left center) and Aphrodite Terra (along the
equator at right center), to show lower values of emissivity than are
typical of lower-lying areas. These low values confirm the high values
of radar reflectivity seen in corresponding regions by the Magellan
altimeter, but do not offer significant additional information to help
solve the considerable puzzle of what mechanism may underlie this
unexpected behavior. On a cooler planet such as Earth or Mars, water or
ice might explain the anomalous observations, but at the 470-degree-
Celsius temperature of the Venus surface, neither can be present. Some
theories require the presence of minerals such as iron pyrites; others
suggest a material, as yet unidentified, that has extremely low
electrical loss. The data shown here were analyzed and projected at the
Center for Space Research, Massachusetts Institute of Technology.