Electro-magnetic radiation which is reflected or emitted from an object is the usual source of remote sensing data. However any media such as gravity or magnetic fields can be utilized in remote sensing.
A device to detect the electro-magnetic radiation reflected or emitted from an object is called a "remote sensor" or "sensor". Cameras or scanners are examples of remote sensors.
A vehicle to carry the sensor is called a "platform". Aircraft or satellites are used as platforms.
The technical term "remote sensing" was first used in the United States in the 1960's, and encompassed photogrammetry, photo-interpretation, photo-geology etc. Since Landsat-1, the first earth observation satellite was launched in 1972, remote sensing has become widely used.
The characteristics of an object can be determined, using reflected or emitted electro-magnetic radiation, from the object. That is, "each object has a unique and different characteristics of reflection or emission if the type of deject or the environmental condition is different."Remote sensing is a technology to identify and understand the object or the environmental condition through the uniqueness of the reflection or emission.
This concept is illustrated in figure 1.1.1 while figure 1.1.2 shows the flow of remote sensing, where three different objects are measured by a sensor in a limited number of bands with respect to their, electro-magnetic characteristics after various factors have affected the signal. The remote sensing data will be processed automatically by computer and/or manually interpreted by humans, and finally utilized in agriculture, land use, forestry, geology, hydrology, oceanography, meteorology, environment etc.
In this chapter, the principles of electro-magnetic radiation are described in sections1.2-1.4, the types of remote sensing with respect to the spectral range of the electro-magnetic, radiation in section 1.5, the definition of radiometry in section 1.6, black body radiation in section 1.7, electro-magnetic characteristics in sections 1.8 and 1.9, solar radiation in section 1.10 and atmospheric behavior in sections 1.11 and 1.12.