The Radiation Framework

Abstract

The acquisition of information about features on the earth’s surface using remote sensing platforms depends on measuring energy emanating from the region of interest so that an image can be formed. The energy can originate from the earth itself, as a result of its finite temperature, or it can be the reflection of energy incident on the earth's surface from an external source such as the sun. It could also come from an artificial source such as a laser or a generator of some other form of radiant energy carried on an aircraft or space craft platform. Irrespective of the energy source used, the principle is to measure upwelling radiation, usually on a pixel by pixel basis, to help understand and map the earth’s surface (and possibly the near sub-surface as seen in Chapt. 5). It is important to look at expressions that describe the actual energy levels generated by the sun and the earth so we know how much is available from common, natural sources. It is of benefit first, though, to look at the means by which energy propagates outwards in free space from a point source generator. This will help in understanding some of the terminology and units used in microwave remote sensing and will be of value when the technology of imaging radar is examined in Chapt. 3.