Remote sensing is a field designed to enable people to look beyond the range of human vision. Whether it is over the horizon, beyond our limited range, or in a spectral range outside our perception, we are in search of information.1 The focus in this text will be on imaging systems of interest for strategic, tactical, and military applications, as well as information of interest to those domains.To begin, consider one of the first airborne remote-sensing images.
Figure 1.1 shows a photograph by Gaspard-Félix Tournachon2 (Tournachon
was also known by his pseudonym, Nadar). He took this aerial photo of Paris
in 1868 from the Hippodrome Balloon, tethered 1700 feet above the city.
Contrast this image with the photo taken by astronauts on Apollo 17, roughly
one hundred years later (Fig. 1.2).
Tournachon’s picture is a fairly classic remote-sensing image—a
representation from a specific place and time of an area of interest. What
sorts of things can be learned from such an image? Where, for instance, are the
streets? What buildings are there? What are the purposes of those buildings?
Which buildings are still there today? These are the elements of information
that people want to extract from such imagery.
The following material establishes a model for extracting information
from remote-sensing data. The examples used here are also meant to illustrate
the range of information that can be extracted from remote-sensing imagery,
as well as some of the consequences of wavelength and resolution choices
made with such systems.