A Remote Sensing is a method of visualizing the radiative properties of the Earth's surface using instrumentation mounted in satellites or aircraft. Remote sensing instrumentation measures the radiation reflected and emitted from the earth at different wavelengths, primarily at those wavelengths not absorbed by the atmosphere. Remotely sensed data can be converted to maps showing the visible or thermal properties of an area.

---

Other /More definition:
A Remote Sensing is the science of obtaining information about an object, area, or phenomenon through the analysis of data acquired by a device (e.g. high altitude photography, satellites) that is not in contact with the object, area, or phenomenon under investigation. Photography is a form of remote sensing. Satellites are a remote sensing platform that collect nearly real-time or periodic imagery for conducting analyses of land cover and land forms based on spectral signatures of various features on the earth.