Chapter 2 Principles Of Remote Sensing Systems

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2-1 Introduction. The principles of remote sensing are based primarily on the proper-

relative to their targets. This chapter provides a background on the physics of remote

sensing, including discussions of energy sources, electromagnetic spectra, atmospheric

effects, interactions with the target or ground surface, spectral reflectance curves, and the

geometry of image acquisition.

2-2 Definition of Remote Sensing.

a. Remote sensing describes the collection of data about an object, area, or phenome-

non from a distance with a device that is not in contact with the object. More commonly,

the term remote sensing refers to imagery and image information derived by both air-

borne and satellite platforms that house sensor equipment. The data collected by the sen-

sors are in the form of electromagnetic energy (EM). Electromagnetic energy is the en-

ergy emitted, absorbed, or reflected by objects. Electromagnetic energy is synonymous to

many terms, including electromagnetic radiation, radiant energy, energy, and radiation.

b. Sensors carried by platforms are engineered to detect variations of emitted and re-

flected electromagnetic radiation. A simple and familiar example of a platform carrying a

sensor is a camera mounted on the underside of an airplane. The airplane may be a high

or low altitude platform while the camera functions as a sensor collecting data from the

ground. The data in this example are reflected electromagnetic energy commonly known

as visible light. Likewise, spaceborne platforms known as satellites, such as Landsat

Thematic Mapper (Landsat TM) or SPOT (Satellite Pour l'Observation de la Terra), carry

a variety of sensors. Similar to the camera, these sensors collect emitted and reflected

electromagnetic energy, and are capable of recording radiation from the visible and other

portions of the spectrum. The type of platform and sensor employed will control the im-

age area and the detail viewed in the image, and additionally they record characteristics

of objects not seen by the human eye.

c. For this manual, remote sensing is defined as the acquisition, processing, and

analysis of surface and near surface data collected by airborne and satellite systems.

2-3 Basic Components of Remote Sensing.

a. The overall process of remote sensing can be broken down into five components.

These components are: 1) an energy source; 2) the interaction of this energy with parti-

cles in the atmosphere; 3) subsequent interaction with the ground target; 4) energy re-

corded by a sensor as data; and 5) data displayed digitally for visual and numerical inter-

pretation. This chapter examines components 14 in detail. Component 5 will be

discussed in Chapter 5. Figure 2-1 illustrates the basic elements of airborne and satellite

remote sensing systems.

2-1

Index