surfaces and that portion which is absorbed and reradiated as thermal energy are
both used in remote sensing analyses. The reflective portion of the spectrum
(0.38–3.0 μm
1 wavelengths) has direct application in remote sensing analyses,
and different wavelength ranges have different applications. Sensors record this
data as images for scientific analysis. Remote sensing methods that measure the
sun’s electromagnetic radiation form the basis for passive remote sensing.
In optical remote sensing, sensors record reflected solar energy as brightness values,
thereby detecting features (both natural and man-made) on the Earth’s surface.
In active remote sensing, instruments transmit man-made radiation to illuminate
the Earth’s surface. The man-made energy reflects off features (both natural and
man-made) and is received and analyzed to form an image. Sonar, radar, and Lidar
are examples of such remote sensing systems. The main focus of this chapter is on
passive remote sensing, i.e., optical remote sensing.
A major consideration for optical remote sensing is atmospheric interference
with incoming radiation—scattering. Scattering specifically refers to radiation
reflected by particles in the atmosphere before it reaches the surface of the Earth.
The level of interference depends on many factors, including:
• The altitude of the aircraft or satellite, i.e., sensors on low-flying aircraft have
less atmosphere to penetrate.
• The wavelength of the radiation—the shorter, blue wavelengths are scattered
about four times as much as the longer, red wavelengths (specifically designated
Rayleigh scattering, caused by larger atmospheric molecules).
• The presence of dust, pollen, water droplets, and smoke (designated Mie
scattering).
• The presence of larger airborne particles (designated non-selective scattering).
All factors noted above cause scattering but the form and magnitude of the
scattering vary.
Another key consideration is the amount of reflected radiation from the features
(both natural and man-made) on the surface of the Earth. When energy reaches the
Earth’s surface, it is either reflected, retransmitted, or absorbed. Different objects
and features reflect or re-emit radiation in various ways. Observing or measuring
these properties establishes spectral properties of individual objects (their spectral
signatures). A particular object’s spectral properties vary either over the course of a
day, from night to day, over the course of a year, or over the course of several years.
Variation in spectral properties allows remote sensing analysis to distinguish
objects/features from one another and compare changes between the same object/
feature over time.
Figure 2 shows the spectral properties of two features—healthy vegetation and
clear, calm water. The y-axis represents percent of reflected energy. The x-axis
1 All wavelength ranges discussed within this chapter are approximations. Different disciplines
define the specific divisions of the electromagnetic spectrum in various wavelengths. Most
definitions are extremely close in value.
Land Use/Land Cover Monitoring and Geospatial Technologies: An Overview
7
both used in remote sensing analyses. The reflective portion of the spectrum
(0.38–3.0 μm
1 wavelengths) has direct application in remote sensing analyses,
and different wavelength ranges have different applications. Sensors record this
data as images for scientific analysis. Remote sensing methods that measure the
sun’s electromagnetic radiation form the basis for passive remote sensing.
In optical remote sensing, sensors record reflected solar energy as brightness values,
thereby detecting features (both natural and man-made) on the Earth’s surface.
In active remote sensing, instruments transmit man-made radiation to illuminate
the Earth’s surface. The man-made energy reflects off features (both natural and
man-made) and is received and analyzed to form an image. Sonar, radar, and Lidar
are examples of such remote sensing systems. The main focus of this chapter is on
passive remote sensing, i.e., optical remote sensing.
A major consideration for optical remote sensing is atmospheric interference
with incoming radiation—scattering. Scattering specifically refers to radiation
reflected by particles in the atmosphere before it reaches the surface of the Earth.
The level of interference depends on many factors, including:
• The altitude of the aircraft or satellite, i.e., sensors on low-flying aircraft have
less atmosphere to penetrate.
• The wavelength of the radiation—the shorter, blue wavelengths are scattered
about four times as much as the longer, red wavelengths (specifically designated
Rayleigh scattering, caused by larger atmospheric molecules).
• The presence of dust, pollen, water droplets, and smoke (designated Mie
scattering).
• The presence of larger airborne particles (designated non-selective scattering).
All factors noted above cause scattering but the form and magnitude of the
scattering vary.
Another key consideration is the amount of reflected radiation from the features
(both natural and man-made) on the surface of the Earth. When energy reaches the
Earth’s surface, it is either reflected, retransmitted, or absorbed. Different objects
and features reflect or re-emit radiation in various ways. Observing or measuring
these properties establishes spectral properties of individual objects (their spectral
signatures). A particular object’s spectral properties vary either over the course of a
day, from night to day, over the course of a year, or over the course of several years.
Variation in spectral properties allows remote sensing analysis to distinguish
objects/features from one another and compare changes between the same object/
feature over time.
Figure 2 shows the spectral properties of two features—healthy vegetation and
clear, calm water. The y-axis represents percent of reflected energy. The x-axis
1 All wavelength ranges discussed within this chapter are approximations. Different disciplines
define the specific divisions of the electromagnetic spectrum in various wavelengths. Most
definitions are extremely close in value.
Land Use/Land Cover Monitoring and Geospatial Technologies: An Overview
7