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Remote sensing is the art and science of recording, measuring, and analyzing information about a phenomenon from a distance. Humans with the aid of their eyes, noses, and ears are constantly seeing, smelling, and hearing things from a distance as they move through an environment. Thus, humans are naturally designed to be remote sensors. In order to study large areas of the Earth’s surface geographers use devices known as remote sensors. These sensors are mounted on platforms such as helicopters, planes, and satellites that make it possible for the sensors to observe the Earth from above.
TYPES OF SENSORS
Two types of sensors exist, namely passive and active. A passive sensor system needs an external energy source . In most cases this source is the sun. These sensors generally detect reflected and emitted energy wave lengths from a phenomenon. An active sensor system provides its own energy source. As an example, a radar sensor sends out sound waves and records the reflection waves coming back from the surface. Passive systems are much more common than active systems.
Most sensors record information about the Earth’s surface by measuring the transmission of energy from the surface in different portions of the electromagnetic (EM) spectrum. Because the Earth’s surface varies in nature, the transmitted energy also varies. This variation in energy allows images of the surface to be created. Human eyes see this variation in energy in the visible portion of the EM spectrum. Sensors detect variations in energy in both the visible and non-visible areas of the spectrum.
Energy waves in certain sections of the EM spectrum easily pass through the atmosphere, while other types do not. The ability of the atmosphere to allow energy to pass through it is referred to as its transmissivity, and varies with the wavelength/type of the radiation. The gases that comprise our atmosphere absorb energy in certain wavelengths while allowing energy with differing wavelengths to pass through.
ABSORPTION BANDS AND ATMOSPHERIC WINDOWS
The areas of the EM spectrum that are absorbed by atmospheric gases such as water vapor, carbon dioxide, and ozone are known as absorption bands.
absorption bands (shown in brown) are represented by a low transmission value that is associated with a specific range of wavelengths. Trying to obtain remotely sensed imagery in the absorption bands is nearly impossible; thus, sensors are generally designed not to record information in these portions of the spectrum.
In contrast to the absorption bands, there are areas of the EM spectrum where the atmosphere is transparent (little or no absorption of energy) to specific wavelengths. These wavelength bands are known as atmospheric "windows" since they allow the energy to easily pass through the atmosphere to Earth's surface. It is in these windows that sensors are used to gather information about Earth phenomena.
Most remote sensing instruments on aircraft or space-based platforms operate in one or more of these windows by making their measurements with detectors tuned to specific frequencies (wavelengths) that pass through the atmosphere. When a remote sensing instrument has a line-of-sight with an object that is reflecting sunlight or emitting heat, the instrument collects and records the radiant energy. While most remote sensing systems are designed to collect reflected energy, some sensors, especially those on meteorological satellites, directly measure absorption phenomena, such as those associated with carbon dioxide (CO2) and other gases. The atmosphere is nearly opaque to EM energy in part of the mid-IR and all of the far-IR regions. In the microwave region, by contrast, most of this radiation moves through unimpeded, so radar waves reach the surface (although weather radars are able to detect clouds and precipitation because they are tuned to observe backscattered radiation from liquid and ice particles).
MAJOR REGIONS OF EMS
Remote sensing is the art and science of recording, measuring, and analyzing information about a phenomenon from a distance. Humans with the aid of their eyes, noses, and ears are constantly seeing, smelling, and hearing things from a distance as they move through an environment. Thus, humans are naturally designed to be remote sensors. In order to study large areas of the Earth’s surface geographers use devices known as remote sensors. These sensors are mounted on platforms such as helicopters, planes, and satellites that make it possible for the sensors to observe the Earth from above.
TYPES OF SENSORS
Two types of sensors exist, namely passive and active. A passive sensor system needs an external energy source . In most cases this source is the sun. These sensors generally detect reflected and emitted energy wave lengths from a phenomenon. An active sensor system provides its own energy source. As an example, a radar sensor sends out sound waves and records the reflection waves coming back from the surface. Passive systems are much more common than active systems.
Most sensors record information about the Earth’s surface by measuring the transmission of energy from the surface in different portions of the electromagnetic (EM) spectrum. Because the Earth’s surface varies in nature, the transmitted energy also varies. This variation in energy allows images of the surface to be created. Human eyes see this variation in energy in the visible portion of the EM spectrum. Sensors detect variations in energy in both the visible and non-visible areas of the spectrum.
Energy waves in certain sections of the EM spectrum easily pass through the atmosphere, while other types do not. The ability of the atmosphere to allow energy to pass through it is referred to as its transmissivity, and varies with the wavelength/type of the radiation. The gases that comprise our atmosphere absorb energy in certain wavelengths while allowing energy with differing wavelengths to pass through.
ABSORPTION BANDS AND ATMOSPHERIC WINDOWS
The areas of the EM spectrum that are absorbed by atmospheric gases such as water vapor, carbon dioxide, and ozone are known as absorption bands.
absorption bands (shown in brown) are represented by a low transmission value that is associated with a specific range of wavelengths. Trying to obtain remotely sensed imagery in the absorption bands is nearly impossible; thus, sensors are generally designed not to record information in these portions of the spectrum.
In contrast to the absorption bands, there are areas of the EM spectrum where the atmosphere is transparent (little or no absorption of energy) to specific wavelengths. These wavelength bands are known as atmospheric "windows" since they allow the energy to easily pass through the atmosphere to Earth's surface. It is in these windows that sensors are used to gather information about Earth phenomena.
Most remote sensing instruments on aircraft or space-based platforms operate in one or more of these windows by making their measurements with detectors tuned to specific frequencies (wavelengths) that pass through the atmosphere. When a remote sensing instrument has a line-of-sight with an object that is reflecting sunlight or emitting heat, the instrument collects and records the radiant energy. While most remote sensing systems are designed to collect reflected energy, some sensors, especially those on meteorological satellites, directly measure absorption phenomena, such as those associated with carbon dioxide (CO2) and other gases. The atmosphere is nearly opaque to EM energy in part of the mid-IR and all of the far-IR regions. In the microwave region, by contrast, most of this radiation moves through unimpeded, so radar waves reach the surface (although weather radars are able to detect clouds and precipitation because they are tuned to observe backscattered radiation from liquid and ice particles).
MAJOR REGIONS OF EMS
Region Name Wavelength Comments Gamma Ray <0.03 nanometers Entirely absorbed by the Earth's atmosphere and not available for remote sensing. X-ray 0.03 to 30 nanometers Entirely absorbed by the Earth's atmosphere and not available for remote sensing. Ultraviolet 0.03 to 0.4 micrometers Wavelengths from 0.03 to 0.3 micrometers absorbed by ozone in the Earth's atmosphere. Photographic U.V 0.3 to 0.4 micrometers Available for remote sensing the Earth. Can be imaged with cameras and sensors. Visible 0.4 to 0.7 micrometers Available for remote sensing the Earth. Can be imaged with cameras and sensors. Near and Mid Infrared 0.7 to 3.0 micrometers Available for remote sensing the Earth. Can be imaged with cameras and sensors. Thermal Infrared <0.7 to 3.0 micrometers Available for remote sensing the Earth. This wavelength cannot be captured by film cameras. Sensors are used to image this wavelength band Micowave or Radar 0.1 to 100 centimeters Longer wavelengths of this band can pass through clouds, fog, and rain. Images using this band can be made with sensors that actively emit microwaves. Radio >100 centimeters Not normally used for remote sensing the Earth. |
Last edited by Admin on Sat Mar 28, 2020 11:01 am; edited 4 times in total (Reason for editing : UPDATING THE TOPIC)