Microwaves can be used for more than just cooking meals. A microwave is an electromagnetic wave with a very long wave length. By scanning the Earth using microwaves, geographers get a unique type of map. Because of the long wave length, these types of maps are generally not very detailed. However, they are very useful in depicting the characteristics that exist beneath the surface of the Earth.
Using radar, geographers can effectively map out the terrain of a territory. Radar works by sending out radio signals, and then waiting for them to bounce off the ground and return. By measuring the amount of time it takes for the signals to return, it is possible to create a very accurate topographic map. An important advantage to using radar is that it can penetrate thick clouds and moisture. This allows scientists to accurately map areas such as rain forests that are otherwise too obscured by clouds and rain.
Sonar works in a similar manner as radar. However, instead of sending out radio waves, researchers send out sound waves. By measuring the time it takes for these sound waves to travel towards an object, bounce off of it, and then return, it is possible to calculate distances. Sonar sensing is used in water. This allows scientists to accurately map the two thirds of the Earth that is under water. One common use of sonar sensing is in fishing boats. By using sonar, a small onboard computer calculates the depth of a lake, and also the location of nearby fish.