Magellan: The Unveiling of Venus

How synthetic aperture radar (SAR) works: Any point in the radar map image can be located by using two measurements-the distance to the point (determined by the time it takes for the radar signals to return to Magellan), and the amount of Doppler shift in the signal (a shift in the frequency caused by the spacecraft's motion along its orbit).

How synthetic aperture radar (SAR) works: Any point in the radar map image can be located by using two measurements-the distance to the point (determined by the time it takes for the radar signals to return to Magellan), and the amount of Doppler shift in the signal (a shift in the frequency caused by the spacecraft's motion along its orbit). However two widely separately points (such as A and B shown here) have the same delay and Doppler shift. Consequently, to avoid confusion between these two points, Magellan's SAR antenna will be pointed to the left of the orbital ground track to illuminate only one of these possible points (A as shown here, B will have already been mapped in a previous orbit's swath.) The resulting radar map will therefore show only features to the left on the ground track. The portion of the Venusian surface shown here is a radar image from the Soviet Venera mission.

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