and the technical underpinning for the reader to understand applications presented
in Chaps. 2–4. This chapter also presents a fundamental basis for Chaps. 14 and 15.
1.1.1 Visible and Infrared Imaging Systems
In remote sensing, a sensor records the intensity of light reflected from a distant
object in several spectral bands. The resulting spectral response ‘‘signature’’ is
used to provide the identity and other information about the object. This is possible
because in principle every object exhibits a unique characteristic spectral response
pattern. This pattern is a function of the object’s structure and component materials, as well as the electromagnetic energy falling on the object. The spectral
response pattern can be so characteristic of the object’s physical and chemical
properties that it provides a spectral signature with which to identify the object.
Most people are familiar with the concept of spectral response in the form of
color. The human eye has specialized cells (cones) that are generally sensitive to
three colors: blue, green, and red. If an object, such as a plant, absorbs blue and red
light and reflects green light, then only green light is available to be seen, only the
green cones are stimulated, and the object thus appears green to human perception.
By design, color film photography replicates the sensitivity of the human eye.
In this case, the light entering a camera induces chemical change on the photographic film, with blue, green, and red light each inducing different specific
changes. Through chemical processing and developing, the film is converted to a
‘‘true color’’ representation of the scene originally imaged in the camera’s field of
view.
Digital photographs mimic the color of those derived from analog film. In a
digital camera, light captured by a photosensitive element induces an electrical
charge with an intensity that is proportional to the incident light intensity. In
modern digital cameras, millions of photosensitive elements are arranged in a twodimensional array; the individual elements are referred to as picture elements, or
pixels. The charge induced in each pixel is converted to a numerical value that is
recorded digitally. These components are often referred to as charge-coupleddevices (CCD). Together, this array of digital values represents the image captured
by the camera. The actual photosensitive elements are typically made of silicon,
which is sensitive to light across the visible and near-infrared (NIR) portions of the
spectrum (400–700 and 700–1,000 nm, respectively; Fig. 1.1). Optical filters are
used to limit and separate the wavelengths reaching the detector array into blue
(*400–500 nm), green (*500–600 nm), and red (*600–700 nm). The result is a
set of three images that are composited as red: green: blue (RGB) to produce a true
color scene. It is useful to note that different optical filters could be employed so
that the camera would image a different set of wavelengths, for example the
infrared.
Spectral imaging follows the same principle and often utilizes the same technology as digital photography. The main conceptual differences are that generally
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S. R. Phinn et al.
in Chaps. 2–4. This chapter also presents a fundamental basis for Chaps. 14 and 15.
1.1.1 Visible and Infrared Imaging Systems
In remote sensing, a sensor records the intensity of light reflected from a distant
object in several spectral bands. The resulting spectral response ‘‘signature’’ is
used to provide the identity and other information about the object. This is possible
because in principle every object exhibits a unique characteristic spectral response
pattern. This pattern is a function of the object’s structure and component materials, as well as the electromagnetic energy falling on the object. The spectral
response pattern can be so characteristic of the object’s physical and chemical
properties that it provides a spectral signature with which to identify the object.
Most people are familiar with the concept of spectral response in the form of
color. The human eye has specialized cells (cones) that are generally sensitive to
three colors: blue, green, and red. If an object, such as a plant, absorbs blue and red
light and reflects green light, then only green light is available to be seen, only the
green cones are stimulated, and the object thus appears green to human perception.
By design, color film photography replicates the sensitivity of the human eye.
In this case, the light entering a camera induces chemical change on the photographic film, with blue, green, and red light each inducing different specific
changes. Through chemical processing and developing, the film is converted to a
‘‘true color’’ representation of the scene originally imaged in the camera’s field of
view.
Digital photographs mimic the color of those derived from analog film. In a
digital camera, light captured by a photosensitive element induces an electrical
charge with an intensity that is proportional to the incident light intensity. In
modern digital cameras, millions of photosensitive elements are arranged in a twodimensional array; the individual elements are referred to as picture elements, or
pixels. The charge induced in each pixel is converted to a numerical value that is
recorded digitally. These components are often referred to as charge-coupleddevices (CCD). Together, this array of digital values represents the image captured
by the camera. The actual photosensitive elements are typically made of silicon,
which is sensitive to light across the visible and near-infrared (NIR) portions of the
spectrum (400–700 and 700–1,000 nm, respectively; Fig. 1.1). Optical filters are
used to limit and separate the wavelengths reaching the detector array into blue
(*400–500 nm), green (*500–600 nm), and red (*600–700 nm). The result is a
set of three images that are composited as red: green: blue (RGB) to produce a true
color scene. It is useful to note that different optical filters could be employed so
that the camera would image a different set of wavelengths, for example the
infrared.
Spectral imaging follows the same principle and often utilizes the same technology as digital photography. The main conceptual differences are that generally
4
S. R. Phinn et al.