I-2
To help remember the principal ideas within this definition,
make a list of key words in it.
ANSWER
This is a rather lengthy and all-inclusive definition.
Perhaps two more simplified definitions are in order:
The first, more general, includes in the term this
idea: Remote Sensing involves gathering data and information
about the physical "world" by detecting
and measuring radiation, particles, and fields associated
with objects located beyond the immediate vicinity
of the sensor device(s). The second is more restricted
but is pertinent to most of the subject matter of
this Tutorial: Remote Sensing is a technology for
sampling electromagnetic radiation to acquire and
interpret non-immediate geospatial data from which
to extract information about features, objects, and
classes on the Earth's land surface, oceans, and atmosphere
(and, where applicable, on the exteriors of other
bodies in the solar system, or, in the broadest framework,
celestial bodies such as stars and galaxies).
I-3
What is the meaning of "geospatial"? Are
there any differences in meaning of the terms "features",
"objects", and "classes"?
ANSWER
Or, try this variation: Applied terrestrial Remote
Sensing involves the detecting and measuring of electromagnetic
energy (usually photons) emanating from distant objects
made of various materials, so that the user can identify
and categorize these objects by class or type, substance,
and spatial distribution.
All of these statements are valid and, taken together,
should give you a reasonable insight into the meaning
and use of the term "Remote Sensing".
Thus, some technical purists arbitrarily stretch the
scope or sphere of remote sensing to include other
measurements of physical propeties from sources "at
a distance" that are more properly included in
the general term "geophysics". This would
take in such geophysical methods as seismic, magnetic,
gravitational, acoustical, and nuclear decay radiation
surveys. Magnetic and gravitational measurements respond
to variations in field forces, so these can be carried
out from satellites. Remote sensing, as defined in
this context, would be a subset within the branch
of science known as Geophysics. However, practitioners
of remote sensing, in its narrower meaning, tend to
exclude these other areas of geophysics from their
understanding of the meaning implicit in the term.
Still, space systems - mostly on satellites - have
made enormous contributions to regional and global
geophysical surveys. This is because it is very difficult
and costly to conduct ground and aerial surveys over
large areas and then to coordinate the individual
surveys by joining them together. To obtain coherent
gravity and magnetic data sets on a world scale, operating
from the global perspective afforded by orbiting satellites
is the only reasonable alternate way to provide total
coverage.
One could argue that this subject deserves a Section
of its own but in the remainder of this Tutorial we
choose to confine our attention to those systems that
produce data by measuring in the electromagnetic radiation
(EMR) spectrum (principally in the Visible, Infrared,
and Radio regions). Nevertheless, just to "peak
at" the kinds of non-EMR geophysical data being
collected from space, we will taken a "detour"
from the main theme of this Section by providing on
the next page several examples of the use of satellite
instruments to obtain information on particles and
fields around the Earth; in Sections 19 and 20 (Planets
and Cosmology) there will also be some illustrations
of several types of geophysical measurements.
For
a comprensive tutorial visit Remote
Sensing Tutorial website.
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