The Viking lander‐to‐orbiter relay links make it possible to perform measurements of the electrical properties of the Martian surface by the bistatic technique. The electromagnetic signals radiated by the lander antenna at 381 MHz, in fact, reach the orbiter both directly and after reflection from the Martian terrain as the orbiter rises and sets with respect to the lander. The fading pattern of the signal intensity received at the orbiter therefore contains information on the reflection coefficient of the terrain and hence on the relative dielectric constant er and the conductivity σ in the vicinity of the lander. The signal amplitude's fading patterns collected with the Lander 1 to Orbiter 1 relay link were of good quality and led to the determination of εr = 3.3 ± 0.7 in the vicinity of Lander 1 (when the quasi‐specular theory was used and σ was assumed to be between 10−3 and 1.0−5 mho/m). These electrical properties are similar to those of pumice and tuff. The dielectric constant of the surface near the Lander 2 site is estimated to be εr = 2.8–12.5.
Approximately 3 months of radio tracking data from the Viking landers have been analyzed to determine the lander locations, the orientation of the spin axis of Mars, and a first estimate from Viking data of the planet's spin rate. Preliminary results have also been obtained for atmospheric parameters and radii at occultation points and for properties of the surface in the vicinity of lander 1.
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