The remotely-sensed images obtained from the satellites are widely used for study of the land, ocean, atmosphere etc. The use of remotely-sensed data, which are inherently digital, demands a degree of mathematical and statistical skill plus familiarity with digital computers. The sensors mounted on-board aircraft and satellites have to be capable of detecting radiance level ranging from low (for example, over oceans) to very high (for example, over snow or ice). For any particular area that is being imaged it is unlikely that the full dynamic range of the sensor will be used.