Imagine that alien astronomers once lived on Venus and studied Earth. With their perpetually cloudy skies they could never see Earth with optical telescopes, but they could study it with radar particularly when Venus was close, between the Sun and Earth. Sending very short pulses at a fixed frequency they looked the shape of the returned pulses in both time and frequency. At this earlier time in Earth history our planet was almost totally covered with water and had just two small continents that were strong radar reflectors. One was at the South Pole and the other near the equator (Hawaii) and essentially all of the returned radar signal came from exposed land and not the ocean. During the Earth day, the Venusians sometimes saw the radar returns as double pulses in time and frequency.