What can you learn about your surroundings from what you see and hear? Sensors in our eyes pick up information from visible light. Sensors in our eardrums record vibrations from sound waves. Both types of sensors receive a stimulus and send information to our brain for interpretation.

Any sensation that is not received through direct contact could be called remote sensing. As a geospatial tool, remote sensing has a slightly more technical definition. In this case, remote sensing means gathering information about the Earth from a distance. Some things are too big for direct study and some places are just too far away. Using remote sensing, we can still study these places.

One familiar method of remote sensing is sonar (SOund NAvigation Ranging). Using sonar, scientists find hills and valleys in the ocean floor without walking on it. To do this, they send out sound waves from a ship. The sound waves bounce off the ocean floor and return as echoes to the ship. By studying the echoes, scientists can identify and map mountains and valleys on the ocean floor below.

Another method of remote sensing is radar (RAdio Detection And Ranging). Radar uses radio waves instead of sound. Radio waves travel far, are invisible to humans and are easy to detect even when they are faint. Just like sound waves, radio waves bounce or reflect off of an object. NASA uses radar to map the Earth and other planets, to track satellites and space debris and to help with things like docking and maneuvering.

Satellite imagery is another form of remote sensing. Objects on Earth give off or reflect infrared and visible light. Using special scanners, some satellites create pictures of the light coming from Earth. Scientists study these images to estimate things like the pattern of plant growth or clouds covering the planet and hurricanes moving across the oceans. Satellite images are an important tool that scientists use to keep track of what is going on around the world.

Visible satellite images are similar to pictures a photographer might record. They display reflected light just as our eyes would see the scene. As long as light is available, land features like mountains, river courses, lakes, silt run-off from rivers into the sea, and coastlines are clearly visible. Since visible imagery depends on available light, it can only be detected during the day, except for the night images showing the distribution of fires and artificial light.

Like radar and sonar, some sensors can capture information from the Earth that we cannot "see" with our eyes. Software is then used to display this information as an image that our eyes can understand. Thermal infrared sensors are one example of sensors that can pick up images we cannot see with our eyes.

Thermal infrared images can display temperature differences. These sensors can collect data both day and night. They show the pattern of heat released from the Earth and heat producing areas such as warm water currents or cities.

Some animals can actually see thermal infrared images. The eyes of South American piranhas are sensitive to infrared light. This helps them see their prey in the brown-stained jungle rivers where they live. If people had the ability to see infrared, they could see the beams from burglar alarm sensors and television remote controls.

NASA uses lidar to map the Earth's surface and analyze the Earth's atmosphere. Lidar is short for Light Detection and Ranging. It works like radar, but uses light waves instead of radio waves to measure the distance to objects. Typical lidar mapping systems bounce a laser light pulse off a surface and record the time it takes for the light to return. This helps determine the distance the light travels. Plants, water, bare exposed earth, and the bottom of a shallow sea each absorb and reflect different colors of light. Most lidars map one or two types of surfaces. NASA's Experimental Advanced Airborne Research Lidar (EAARL) can trace the topography of many different surfaces. EAARL has been used to track hurricane damage in coastal areas because it can distinguish between water, sand and plant life. EAARL helps map changes in sand dunes, inlets, and waterways.

NASA scientists use remote sensing to find out more about the Earth's topography and the effects of human activity on Earth. Landsat 7 is a U.S. satellite gathering remotely sensed images of the Earth's land surface and coasts. This information, and other satellite images, help us learn about Earth's history and predict upcoming changes in the Earth's atmosphere, land and waters. NASA also uses remote sensing to gather information about other planets and objects in our solar system. The Mars Orbiter Laser Altimeter (MOLA) uses remote sensing technology to study the surface of Mars. This technology has gathered key information for NASA researchers to help them understand the Earth's environment, and the environments of other planets.