Two images of Death Valley, California. On the right, an oblique photograph reveals the geography of the valley in a familiar way. The photograph on the right is an aerial photograph with varying colors that highlight he different rock types found along the cliffs and the large salt flats that cover the valley floor.

Unless an object is at absolute zero temperature (-273° C), it will reflect, absorb, and emit energy at unique wavelengths and frequencies. The energy is called electromagnetic radiation. All of the materials on the surface of the earth, the planets, and sun absorb, reflect and emit electromagnetic radiation in waves that travel across distances.

Remote sensing instruments like airplanes and satellites contain sensors to detect the radiation that is being reflected or emitted from an object or material at a distance.

Different objects have different physical characteristics so they reflect or emit energy differently, because of these differences we can identify the material or object without actually being in contact with the object -- just like the strawberry you observed in the beginning of this tutorial.