Geography Reference
In-Depth Information
PRINCIPLES OF GI AND CARTOGRAPHY
Remote Sensing
Chapter 8
Remote Sensing
Remote sensing is the collection of data without directly measuring the
object. It relies on the ref lectance of natural or emitted electromagnetic
radiation (EMR). EMR can be emitted by the sun (natural EMR) and, for
example, sensed by photographic film, or it can be sent by a transmitter and
the returned energy sensed, for example, by radar (a type of emitted EMR).
Remote sensing has become a key means of data collection for a number of
reasons, but mainly because it allows for systematic and accurate collection
of GI.
Remote sensing
is defined very broadly in this chapter as a measurement
of an object's characteristics from a distance using reflected or emitted elec-
tromagnetic energy. This definition means that remote sensing includes all
kinds of photography, aerial imagery, satellite sensors, and any kind of laser
measurement. Remote sensing involves different types of sensor technolo-
gies ranging from photographic emulsions to digital chips. It also involves a
vast array of storage media including everything from photographic film to
computer files. As you can imagine, data from remote sensing and the sen-
sor technologies themselves are a resource that can enhance the work being
done in a number of other fields of study. For example, the discipline of sur-
veying has changed enormously with the introduction of laser-based dis-
tance-finding technology.
The reason for defining remote sensing so broadly is that it is a very
important GI technology. Remote sensing offers three advantages over other
forms of data collection and GI. First, it makes it much easier to systemati-
cally recognize things and events over a large area. Second, it makes it easier
and less costly to revise most maps. Third, digital remote sensing images can
be used directly by other applications. There are some caveats to these
advantages that you will find out about in this chapter. This chapter is purely
introductory in nature and will skim over many of the crucial details and
physics, but you should end up with a solid understanding of what remote
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