"Remote sensing" is a rather familiar activity and part of our daily life. As you view the screen of your computer monitor, you are actively engaged in remote sensing. It only gets complicated when the scale of observation is increased. 

A physical quantity (light) emanates from that screen, of which the imaging electronics provide a source of radiation. The radiated light passes over a distance, and thus is "remote" to some extent, until it encounters and is captured by a sensor (your eyes). Each eye sends a signal to a processor (your brain) which records the data and interprets this into information. Several of the human senses gather their awareness of the external world almost entirely by perceiving a variety of signals, either emitted or reflected, actively or passively, from objects that transmit this information in waves or pulses. Thus, one hears disturbances in the atmosphere carried as sound waves, experiences sensations such as heat (either through direct contact or as radiant energy), reacts to chemical signals from food through taste and smell, and recognizes shapes, colours, and relative positions of exterior objects and classes of materials by means of seeing visible light issuing from them. This occurs in most cases without any direct contact.

In the same way, satellite sensors record the intensity of electromagnetic radiation (sunlight) reflected by objects on the earth at different wavelengths. Energy that is not reflected by an object is absorbed. Remote sensing relies on the fact that particular features of the landscape such as trees, crop, buildings and water reflect light differently in different wavelengths. Grass looks green, for example, because it reflects green light and absorbs other visible wavelengths.

Remote sensing, then, can be defined as the measurements of object properties on the earth's surface using data acquired from aircraft and satellites. It is an attempt to derive information at a distance, rather than in situ. One of the best sentences to introduce the privileged point of view of Remote Sensing belongs to Aristotle's speeches on Metaphysics: "The whole is more than the sum of its part". This is because the perspective obtained from satellites or aircrafts provides an invaluable view of the Earth, that cannot be achieved by the limited views provided by in situ measurements or tools.

Today the main challenge of remote sensing is represented in the formulation of a global vision, both spatial and temporal, of Earth and Cosmos with the goal to contribute to a better understanding of the complex interrelatinos between human activities and changes in nature.

The images derived from remote sensing systems offer a repetitive and consistent view of the Earth, useful for monitoring the whole earth system and the effect of human activities on the earth. Furthermore, the "satellite perspective" has enabled man to capture a privileged viewpoint of events as they evolve through time.

Some of the important applications of remote sensing technology are:

-        environmental assessment and monitoring

-        global change detection and monitoring

-        agriculture

-        non-renewable resource exploration

-        renewable natural resources

-        meteorology

-        mapping

-        military surveillance and reconnaissance

-        news media.

To meet the needs of different data users, there are many remote-sensing systems, offering a wide range of spatial, spectral and temporal parameters. Some users may require frequent, repetitive coverage with relatively low spatial resolution. Others may desire the highest possible spatial resolution, with coverage only infrequent repetition coverage.