Radar is very useful for taking pictures. In order to "see" things in the dark, a satellite must rely on instruments that do not use sunlight to illuminate objects. A camera that uses radar is ideal for seeing in the dark. It can also see all the way down to the surface of the Earth through clouds. The Canadian satellite Radarsat uses something called Synthetic Aperture Radar. This type of equipment is on board only two other satellites in the world.
Radarsat is able to see the Earth better than any previous satellite. Radarsat can, therefore, see through dark, penetrate fog, and look beyond the clouds. Unlike many other satellites that use optical remote sensing and depend on the Earth being in sunlight to get useful pictures, Radarsat's SAR uses microwaves instead. Microwaves are a form of electromagnetic radiation that are beyond the range of the visible light spectrum. They have very high frequencies and wavelengths of 1mm to 50 cm. SAR sends pulsed signals to Earth and then processes the received reflected pulses. Radarsat's SAR-based technology provides its own microwave illumination and thus will operate day or night, regardless of weather conditions.
Since one of Radarsat's main functions is to take photographs of the Earth, it must have a camera. The camera is located at the end of a 15-meter arm, off which the SAR's microwave beams may be transmitted and received at various angles. Therefore, unlike other radar satellites currently in orbit, Radarsat is able to take pictures from various angles other than the overhead view. By modifying the camera angle, Radarsat can capture a range of picture sizes, from 50 to 500 km. This allows different sizes of land masses to be photographed. In addition, Radarsat provides a resolution spanning from 10 to 100 metres, five times wider than any other satellite performing a similar function right now.