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Issue 3: A Tutorial (page 2)

This information is an excerpt from Remote Sensing Tutorial website with the consent of the owner Nicholas M. Short and NASA.

The Concept of Remote Sensing (Continued)

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: http://rst.gsfc.nasa.gov/

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