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Remote sensing is the process of acquiring information about an object or phenomenon without making actual physical contact with it, as opposed to onsite observation or onsite sensing. This often requires the use of aerial sensor technologies such as those used in reconnaissance airplanes and satellites in order to detect and analyze objects on the Earth, usually on the surface.
Remote sensing is the use of satellites, planes and other aerial technologies using advanced sensor technologies able to detect energy reflected from the Earth's surface. This makes it possible to collect data in inaccessible or dangerous areas where it would be too hazardous to bring in a team and equipment to collect data. Since the sensors are high above the Earth, they are very useful for gathering data in a very wide area. Applications of remote sensing include monitoring the extent of deforestation or the spread of an oil spill, as well as monitoring the movement of and changes in polar ice caps and icebergs. The same principle is applied to depth sounding of oceanic and coastal depths from a ship.
The way remote sensing works is that the orbital platforms such as satellites, weather balloons and even planes collect and transmit data from different portions of the electromagnetic spectrum to terrestrial stations that process the data and images for people to analyze and archive. This can be either passive or active. Passive means that the sensors are simply collecting data that are already available such as reflected light and radiation when taking various kinds of images like standard photos and infrared and thermal images. Active sensing means that the sensor or another part of the overall system initiates its own form of signal to be projected to the surface and then collects the reflections, such as firing a laser and then calculating the time it takes to reflect back to the sensor in order to get the distance from the surface to the satellite. This allows researchers to get accurate readings about the depth of a canyon or ravine or to get the height of a natural formation such as a mountain or even buildings.
Technologies and techniques used in remote sensing include: