Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object and thus in contrast to on site observation. Remote sensing is a sub-field of
geography. In modern usage, the term generally refers to the use of aerial sensor technologies to detect and classify objects on Earth (both on the surface, and in the
atmosphere and
oceans) by means of
propagated signals (e.g.
electromagnetic radiation). It may be split into active remote sensing (when a signal is first emitted from
aircraft or
satellites) or passive (e.g. sunlight) when information is merely recorded.