Page 148 - Intro to Space Sciences Spacecraft Applications

Remote Sensing
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himself and his world in a global sense for the first time in history. In
order to continue, it is necessary to describe the physics and processes
employed by space remote sensing systems to gain more detailed infor-
mation of interest to users on earth.

Remote sensing is the collection of information about an object without
being in physical contact with the object. Space-based remote sensors are
also used for reference and control functions such as providing input for
spacecraft attitude control, weapons guidance, spacecraft planetary land-
ing, and spacecraft docking. In the context of this chapter, remote sensing
will be restricted to data collection and to methods that employ electro-
magnetic energy as the means of detecting and measuring target charac-
teristics. This definition excludes electrical, magnetic, and gravity surveys
that measure force fields rather than electromagnetic radiation.
Remote sensing systems employ the electromagnetic spectrum in unique
ways to send and/or collect natural or man-induced signals. The use of par-
ticular wavelengths and signals for remote sensing can be based on:

Natural radiation associated with the phenomena to be observed.
Response of an object or material to an active signal created and trans-
mitted to the target area by the remote sensor.
The use of atmospheric or ionospheric interaction in the vertical path
from the satellite to the earth, creating a class of sensors identified as
sounders.
The avoidance of atmospheric or ionospheric interference.

Earth viewing systems concentrate on the microwave, infrared, and vis-
ible regions of the spectrum from which information can be derived for a
variety of specific imaging categories, including land mapping, specific
target surveillance, and environmental monitoring. In addition to these
more popular and commonly identifiable applications, space remote sen-
sors yield important information on basic geophysical processes such as
atmospheric temperature, water vapor, and liquid water; ocean surface
wave height, length, and dynamics; surface wind speed and direction; sur-
face temperature and ocean color; land area spectral evaluations; topo-
graphic variations; and object or geological classifications.
If the sensor relies primarily on an ability to discern the spatial charac-
teristics of the objects in the field of interest, it is referred to as an hugex