Remote Sensing
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Remote sensing is a technique used to gather information about an object or an area without actually touching it. Our eyes, ears, and skin, as well as more sophisticated instruments, all aid us in remote sensing. These sensors give us information about size, color, location, and temperature. Do you need to touch a radiator to tell if it is hot? From several inches away, the nerve endings in your fingers can discern whether the radiator is on, thus remotely sensing its status. Looking down on the landscape from a tall tree is another form of remote sensing. Looking through a telescope from a ship's crow's nest, scanning the horizon for attackers from a guard tower on a hill, and reconnaissance by horseback were early methods of remote sensing. The first aerial photography for surveying the landscape was done in France in 1848. A few years later, James Wallace Black took photographs of Boston from a balloon at 1,220 feet. Union spies used aerial photography during the Civil War to observe Confederate troop movements. In some cases, the "photographers" were pigeons with cameras strapped to their stomachs!  During World War II, aerial photography, using wavelengths just beyond our visual range (near-infrared), was able to detect camouflaged weapons on the ground. Living vegetation and green-painted camouflage both appeared green through a conventional camera; infrared photos could easily distinguish them. The invention of radar during World War II enabled the Allies to win the air war against a vastly superior Luftwaffe Air Force. Many historians believe Britain was saved by the advance warning of incoming German planes that radar provided. (The word radar comes from radio detection and ranging. It works by sending radio waves at an object and receiving the waves that are reflected by the object.) Modern remote sensing evolved in the 1960s as a by-product of the space program. Today, satellites and computers collect data in wavelengths from ultraviolet to radio regions. Satellite imaging makes it possible to gather massive amounts of data that observers on the ground could not. Information gathered can be processed efficiently by computers that now perform much of the detailed work cartographers used to do by hand. In addition to conventional cameras, which use visible light, satellites transmit images that are generated by heat, electromagnetic radiation, and sound. Infrared imagery uses heat waves, wavelengths beyond the range of visible light (infrared = "beyond red"). Areas of Earth warmed by the heat of the sun, by biological productivity (growing trees, crops, plant plankton), and the heat generated by industrialization (machinery, lights, cars, etc.) are all strong sources of infrared radiation. Commercial uses of infrared sensors include sinks that turn on automatically and toilets that flush automatically. Some burglar alarms are triggered by sensing the heat from intruding bodies. Thermal scans surveying homes for energy efficiency reveal where there are heat leaks. Heat-sensing night goggles were used by the military in Desert Storm to identify enemy targets. Radar uses radio waves to measure the time it takes to send and receive electromagnetic radiation. Unlike TV cameras, radar can be used at night and on cloudy days. Air traffic control is perhaps the most important use of radar, ensuring that planes approaching an airport don't collide with each other. Radar guns are used in law enforcement for calculating the speed of a vehicle and in baseball to measure the speed of a pitch.
There are three major advantages to modern methods of remote sensing:
Remote sensing is used to estimate crop yields, to search for minerals and petroleum deposits, to plot ancient stream beds in the desert, to identify earthquake-prone areas, to chart the meanderings of the Gulf Stream and other currents that affect our weather and climate, and to search for shipwrecks on the ocean floor. Remote sensing helps us gauge how human activities are affecting the planet by documenting the destruction of rain forests, monitoring water temperatures in the ocean, and measuring the warming of the Earth's atmosphere. Satellites can identify whether a field is planted with wheat, oats, cotton, or corn by reading each crop's "spectral signature," the wavelength of light each kind of plant reflects back into the atmosphere. Scientists can also observe some amazing things about crops from a satellite image taken from thousands of miles away. They can tell whether it's just been planted or if it's ready for harvest, if it's is suffering from a disease or is being attacked by pests.This is extremely helpful to farmers with thousands of acres of crops. Students and teachers use the images produced by environmental satellites as tools to inventory land areas, measure species vitality, and plan for the future. Geologists use satellites to prospect for minerals or oil. They look for diagnostic land forms usually associated with their target (for example, shale often traps petroleum deposits between its layers) or they locate traces of minerals on the surface. Each mineral also has its own spectral signature. With the help of such clues, scientists have discovered copper, nickel, zinc, and uranium in the United States; tin in Brazil; and copper in Mexico. Weather satellites record cloud patterns and movements which are important predictors of storms. They also measure temperature, moisture in the atmosphere, air pressure, rainfall, and snow depth. The same satellites can track large fires, wildlife outfitted with radio transmitters, glaciers calving into icebergs, and changes in the size of the hole in the ozone layer. Spy satellites keep track of armies and military build-up, pick up signals from secret agents' transmitters, and send secret coded messages. Early-warning satellites employ infrared sensors to detect the hot exhaust from a nuclear missile within seconds after it is launched. Satellite images provide a broad picture of our planet. They demonstrate how small, interconnected, and fragile it really is. 
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