Introductory Remote Sensing Principles and Concepts
The documents comprises the study of remote sensing, its importants, applications, study of satellites, process of remote sensing, photography images, digital imaging, resolutions.
The science (and art) of acquiring information about an object, area or phenomenon, without
getting in physical contact with it, by sensing and recording reflected or emitted energy and
processing, analyzing, and applying that information.
Our eyes are an excellent example of a remote sensing device. We are able to gather
information about our surroundings by gauging the amount and nature of the reflectance of
visible light energy from some external source (such as the sun or a light bulb) as it reflects off
objects in our field of view. Contrast this with a thermometer, which must be in contact with
the phenomenon it measures, and thus is not a remote sensing device.
As humans, we are intimately familiar with remote sensing in that we rely on visual perception to
provide us with much of the information about our surroundings. As sensors, however, our eyes are
greatly limited by
1. sensitivity to only the visible range of electromagnetic energy;
2. viewing perspectives dictated by the location of our bodies; and
3. the inability to form a lasting record of what we view.
Because of these limitations, humans have continuously sought to develop the technological means
to increase our ability to see and record the physical properties of our environment.
Beginning with the early use of aerial photography, remote sensing has been recognized as a
valuable tool for viewing, analyzing, characterizing, and making decisions about our environment. In
the past few decades, remote sensing technology has advanced on three fronts:
1. from predominantly military uses to a variety of environmental analysis applications that
relate to land, ocean, and atmosphere issues;
2. from (analog) photographic systems to sensors that convert energy from many parts of
the electromagnetic spectrum to electronic signals; and
3. from aircraft to satellite platforms.
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,1. Energy Source or Illumination (A) - the first requirement for remote sensing is to have an
energy source which illuminates or provides electromagnetic energy to the target of interest.
2. Radiation and the Atmosphere (B) - as the energy travels from its source to the target, it will
come in contact with and interact with the atmosphere it passes through. This interaction may
take place a second time as the energy travels from the target to the sensor.
3. Interaction with the Target (C) - once the energy makes its way to the target through the
atmosphere, it interacts with the target depending on the properties of both the target and the
radiation.
4. Recording of Energy by the Sensor (D) - after the energy has been scattered by, or emitted
from the target, we require a sensor (remote - not in contact with the target) to collect and
record the electromagnetic radiation.
5. Transmission, Reception, and Processing (E) - the energy recorded by the sensor has to be
transmitted, often in electronic form, to a receiving and processing station where the data are
processed into an image (hardcopy and/or digital).
6. Interpretation and Analysis (F) - the processed image is interpreted, visually and/or digitally
or electronically, to extract information about the target which was illuminated.
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,7. Application (G) - the final element of the remote sensing process is achieved when we apply
the information we have been able to extract from the imagery about the target in order to
better understand it, reveal some new information, or assist in solving a particular problem.
Aircraft and satellites are the common platforms for remote sensing of the earth and its natural
resources. Aerial photography in the visible portion /band / wavelength of the electromagnetic
spectrum was the original form of remote sensing but technological developments has enabled
the acquisition of information at other wavelengths including near infrared, thermal infrared
and microwave. Collection of information over a large numbers of wavelength bands is referred
to as multispectral or hyperspectral data. The development and deployment of manned and
unmanned satellites has enhanced the collection of remotely sensed data and offers an
inexpensive way to obtain information over large areas. The capacity of remote sensing to
identify and monitor land surfaces and environmental conditions has expanded greatly over the
last few years and remotely sensed data will be an essential tool in natural resource
management.
Electromagnetic Energy and RS
Take an example of a coloured photograph.
The sky is blue, trees green, soil-brown, building roofs (red, silver, green, etc). The sensation of
colour is caused by EM radiation. Red, green, blue, relate to forms of energy which we
commonly refer to as light. Light is EM radiation that is visible to the human eye. The sun emits
light, the earths surface features reflect it, the photosynthetic cells (cones and rods) in our eyes
detect it. Light is not the only form of energy radiated from the sun and other bodies. The
sensation ‘warm’ is caused by thermal emission. Sun tanning or our body generating Vitamin D
is triggered by ultraviolet (UV) radiation.
Electromagnetic waves
Electromagnetic waves transport energy through empty space, stored in the propagating
electric and magnetic fields.
The electromagnetic (EM) spectrum is the continuous range of electromagnetic radiation,
extending from gamma rays (highest frequency & shortest wavelength) to radio waves (lowest
frequency & longest wavelength) and including visible light.
The EM spectrum can be divided into seven different regions —— gamma rays, X-rays,
ultraviolet, visible light, infrared, microwaves and radio waves.
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, The Electromagnetic Spectrum (EM)
The Electromagnetic Spectrum (EM)
Remote sensing involves the measurement of energy in many parts of the electromagnetic
(EM) spectrum. The major regions of interest in satellite sensing are visible light, reflected and
emitted infrared, and the microwave regions. The measurement of this radiation takes place in
what are known as spectral bands. A spectral band is defined as a discrete interval of the EM
spectrum. For example the wavelength range of 0.4μm to 0.5μm (μm = micrometers or 10-6m)
is one spectral band. Satellite sensors have been designed to measure responses within
particular spectral bands to enable the discrimination of the major Earth surface materials.
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