Thick and opaque, the atmosphere of Venus required a method beyond optical survey, to map the surface of the planet.
The resolution of conventional radar depends entirely on the size of the antenna, which is greatly restricted by costs, physical constraints by launch vehicles and the complexity of maneuvering a large apparatus to provide high resolution data.
Magellan addressed this problem by using a method known as synthetic aperture, where a large antenna is imitated by processing the information gathered by ground computers.


The Magellan high-gain parabolic antenna, oriented 28°–78° to the right or left of nadir, emitted thousands of microwave pulses that passed through the clouds and to the surface of Venus, illuminating a swath of land.
The Radar System then recorded the brightness of each pulse as it reflected back off the side surfaces of rocks, cliffs, volcanoes and other geologic features, as a form of backscatter.
 To increase the imaging resolution, Magellan recorded a series of data bursts for a particular location during multiple instances called, "looks".
 Each "look" slightly overlapped the previous, returning slightly different information for the same location, as the spacecraft moved in orbit.
 After transmitting the data back to Earth, Doppler modeling was used to take the overlapping "looks" and combine them into a continuous, high resolution image of the surface.
Thick and opaque, the atmosphere of Venus required a method beyond optical survey, to map the surface of the planet. The resolution of conventional radar depends entirely on the size of the antenna, which is greatly restricted by costs, physical constraints by launch vehicles and the complexity of maneuvering a large apparatus to provide high resolution data. Magellan addressed this problem by using a method known as synthetic aperture, where a large antenna is imitated by processing the information gathered by ground computers.

The Magellan high-gain parabolic antenna, oriented 28°–78° to the right or left of nadir, emitted thousands of microwave pulses that passed through the clouds and to the surface of Venus, illuminating a swath of land. The Radar System then recorded the brightness of each pulse as it reflected back off the side surfaces of rocks, cliffs, volcanoes and other geologic features, as a form of backscatter.  To increase the imaging resolution, Magellan recorded a series of data bursts for a particular location during multiple instances called, "looks".  Each "look" slightly overlapped the previous, returning slightly different information for the same location, as the spacecraft moved in orbit.  After transmitting the data back to Earth, Doppler modeling was used to take the overlapping "looks" and combine them into a continuous, high resolution image of the surface.
Magellan (spacecraft)