Radar (RAdio Detection And Ranging) is similar to sonar, but uses radio waves. Lidar (Light Detection and Ranging, or “light” plus “radar”) uses infrared, visual, or ultraviolet light waves. This usually involves a laser, and can collect quite detailed data. For instance, one way that lidar is used is topographical mapping. By shining a laser at the terrain, scientists can measure the length of the beam reflected back to them. Once they know the length of the reflected beam, they know how far down the beam had to travel before it was reflected back, which will tell them the elevation of the Earth at that specific location. By taking many of these measurements, they can make a precise topographical map of the Earth.
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