Remote sensing is a technique used to gather information about an object without actually touching it. We practice remote sensing with our eyes, ears, and even our skin. These sensors obtain information about the size, color, location, and temperature of objects.
Television also is a form of remote sensing. A TV camera acts as a sensor when it picks up an image and transmits it to a studio. The image is then relayed by cable, broadcasting station, or satellite into viewers’ homes. Sensors similar to TV cameras are flown in aircraft and satellites. They relay images of the earth to stations on the ground. Cloud maps used on TV weather forecasts are created from images relayed by satellites about 22,300 miles (35,900 kilometers) above the earth.
Some sensors detect invisible forms of energy, especially infrared rays (heat rays) that the earth sends out. A computer converts the data into images for study on TV screens or in photographs. The colors created by computer are called false colors because they do not correspond to the colors we normally see. Radar is a sensor that uses radio waves to make images of the planets (see Radar ). Sonar uses sound waves to map the ocean floor and search for sunken ships (see Sonar ).
Remote sensing is useful for obtaining information about the earth. Images from satellites are used for estimating crop yields and searching for mineral and petroleum deposits. Remote sensing also helps scientists understand how human activity affects the environment. For example, sensors monitor the health of forests threatened by pollution, map the destruction of tropical rain forests, and measure the warming of the earth’s atmosphere known as the greenhouse effect (see Greenhouse effect ). We can even learn about past environments. Imaging radar has mapped stream channels under the Sahara in southern Egypt, showing that this desert once had a wetter climate.
