What is remote sensing? what are its application and various types of remote sensing in detail with graphic visuals.

1. Remote Sensing and GIS
Dr. Sanjeev Kumar
Department of Geology
School of Earth and Environmental Sciences
Babasaheb Bhimrao Ambedkar University, Lucknow
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Definition of Remote Sensing
A formal and comprehensive definition of applied remote sensing as given
by National Aeronautics and Space Administration (NASA) is as follows:
“The acquisition and measurement of data/information on some
property(ies) of a phenomenon object, or material by a recording device
not in physical intimate contact with the feature(s) under surveillance;
technique involve amassing knowledge pertinent to environments by
measuring force fields electromagnetic radiation or acoustic energy
employing cameras, radiometers and scanners, lasers, radio frequency
receivers, radar system, sonar, thermal devices, seismographs,
magnetometers, gravimeters, scintillometers, and other instrument”.

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Another definitions:
"Remote Sensing is the science and art of obtaining information about an object, area, or
phenomenon through the analysis of data acquired by a device that is not in contact with
the object, area, or phenomenon under investigation.“
or
Remote sensing is the acquisition of information about an object or phenomenon without
making physical contact with the object and thus in contrast to on-site observation.
The another definition of remote sensing is given by American
Association of Photogrammetry and Remote Sensing 1988 as follows:
“The art, science and technology of obtaining reliable
information about physical objects and the environment, through the
process of recording, measuring and interpreting imagery and digital
representation of energy pattern derived from noncontact sensor
systems”.

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2005: IRS cartosat for DEM generation
2007: IRS cartosat 2 with 80 cm panchromatic band
2013: Landsat 8 OL1/T/RS with 11 bands (freely downlodable)
2014: World view 3.30 resolution

6. Stages in Remote Sensing
i. Emission of electromagnetic radiation, or EMR (sun/self emission)
ii. Transmission of energy from the source to the surface of the earth, as
well as absorption and scattering
iii. Interaction of EMR with the earth’s surface: reflection and emission
iv. Transmission of energy from the surface to the remote sensor
v. Sensor data output
vi. Data transmission, processing and analysis
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7. • Energy Source or Illumination (A)
• Radiation and the Atmosphere (B)
• Interaction with the Target (C)
• Recording of Energy by the Sensor (D)
• Transmission, Reception, and Processing (E)
• Interpretation and Analysis (F)
• Application (G)
Remote Sensing Process Components
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Applications of Remote Sensing

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13. Electromagnetic Radiation
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15. Electromagnetic Energy
Wave Theory - c = 𝜆 x 𝜐
Speed of Light (c) = wavelength x frequency (𝜆 x 𝜐)
c = 3 x 108 m/sec (the speed of light) = 186,000 miles/sec
Wavelength (𝜆) – the distance from
one wave peak (or crest) to the next
is the wavelength
Frequency (𝜐) - the number of
peaks passing a fixed point in a
space per a given time unit
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16. Electromagnetic Spectrum
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Major regions of the electromagnetic spectrum

23. Types of Remote Sensing
Remote Sensing can be either passive or active. ACTIVE systems have
their own source of energy (such as RADAR) whereas the PASSIVE
systems depend upon external source of illumination (such as SUN) or
self emission for remote sensing. This is described is given below:
Active remote sensing: Emits energy in order to scan objects and
areas whereupon a sensor then detects and measures the radiation that is reflected
or backscattered from the target. RADAR is an example of active remote sensing
where the time delay between emission
and return is measured, establishing the
location, height, speeds and direction of
an object.
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Active remote sensing create their own electromagnetic energy that
1. Is transmitted from the sensor toward the terrain (and is largely
unaffected by the atmosphere)
2. Interacts with the terrain producing a backscatter of energy
3. Is recorded by the remote sensor’s receiver.
The most widely used active remote sensing include:
• Active microwave (Radio detection and ranging; RADAR ),
which is based on the transmission of long wavelength microwaves (e.g.
3-25 cm.) through the atmosphere and then recording the amount of
energy backscattered from the terrain.
Radar was investigated by A.H. Taylor and L.C. Young in 1922.

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• SONAR (Sound navigation ranging), which is based on the
transmission of sound waves through a water column and then recording the
amount of energy backscattered from the bottom or from objects within the
water column
• LIDAR (Light detection and ranging), which is based on the
transmission of relatively short wave length laser light (e.g. 1040 nm)
and then recording the amount of light backscattered from the terrain.

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31. Passive Remote Sensing: detect natural radiation that is emitted or
reflected by the object or surrounding area being observed. Reflected sunlight
is the most common source of radiation measured by passive sensors.
Examples of passive remote sensors include film photograph, infrared, and
radiometers.
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Special Sensor Microwave/ Imager (SSM/I)
• One of the first passive microwave sensors was the Special sensor
Microwave/ imager (SSM/I) onboard the Defense Meteorological Satellite
Program (DMSP) satellite since 1987. The department of defense also release
the data to the scientific community.
TRMM Microwave Imager (TMI)
• The Tropical Rainfall Measuring Mission (TRMM) is sponsored by NASA
and the National Space Development Agency (NASAD) of Japan to study
the tropical rainfall and the associated release of energy that helps to power
global atmospheric circulation.
• The TRMM Microwave Imager is a passive microwave sensor designed to
provide quantitative rainfall information over a 487 mile (780 km.) swath.
• It measures the intensity of radiation at five frequencies : 10.7 (45 km
spatial resolution), 19.4, 21.3, 37, 85.5 GHz (5 km spatial resolution).

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Advanced Microwave Scanning Radiometer (AMSR-E)
AMSR- E measures total water-vapor content, total liquid water content,
precipitation, snow-water equivalent, soil moisture (using the 6.925 and 10.65
GHz frequencies), sea surface temperature (SST), sea surface wind speed, and
sea ice extent.

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Types of Remote Sensing System
1. Visual remote Sensing System:

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2. Optical remote Sensing System:

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Optical remote sensing systems are classified into the following types, depending on the
number of spectral bands used in the imaging process.
Panchromatic imaging system: The sensor is a single channel detector sensitive to radiation
within a broad wavelength range. If the wavelength range coincide with the visible range,
then the resulting image resembles a "black-and-white" photograph taken from space. The
physical quantity being measured is the apparent brightness of the targets. The spectral
information or "colour" of the targets is lost. Examples of panchromatic imaging systems are:
• IKONOS PAN
• SPOT HRV-PAN
Multispectral imaging system: The sensor is a multichannel detector with a few spectral
bands. Each channel is sensitive to radiation within a narrow wavelength band. The resulting
image is a multilayer image which contains both the brightness and spectral (colour)
information of the targets being observed. Examples of multispectral systems are:
• LANDSAT MSS
• LANDSAT TM
• SPOT HRV-XS
• IKONOS MS

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Superspectral Imaging Systems: A superspectral imaging sensor has many more
spectral channels (typically >10) than a multispectral sensor. The bands have narrower
bandwidths, enabling the finer spectral characteristics of the targets to be captured by the
sensor. Examples of superspectral systems are:
• MODIS
• MERIS
Hyperspectral Imaging Systems: A hyperspectral imaging system is also known as an
"imaging spectrometer". It acquires images in about a hundred or more contiguous spectral
bands. The precise spectral information contained in a hyperspectral image enables better
characterization and identification of targets. Hyperspectral images have potential
applications in such fields as precision agriculture (e.g. monitoring the types, health, moisture
status and maturity of crops), coastal management (e.g. monitoring of phytoplanktons,
pollution, bathymetry changes). An example of a hyperspectral system is:
• Hyperion on EO1 satellite

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3. Infrared Remote Sensing:

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The amount of thermal radiation emitted at a particular wavelength from a warm object
depends on its temperature. If the earth's surface is regarded as a blackbody emitter, its
apparent temperature (known as the brightness temperature) and the spectral radiance are
related by the Planck's blackbody equation, plotted in the above figure for several
temperatures. For a surface at a brightness temperature around 300 K, the spectral radiance
peaks at a wavelength around 10 µm. The peak wavelength decreases as the brightness
temperature increases. For this reason, most satellite sensors for measurement of the earth
surface temperature have a band detecting infrared radiation around 10 µm.
Besides the measurement of regular surface temperature, infrared
sensors can be used for detection of forest fires or other warm/hot objects. For typical fire
temperatures from about 500 K (smouldering fire) to over 1000 K (flaming fire), the
radiance versus wavelength curves peak at around 3.8 µm. Sensors such as the NOAA-
AVHRR, ERS-ATSR and TERRA-MODIS are equipped with this band that can be used
for detection of fire hot spots.

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Planck's law describes the spectral density of electromagnetic radiation emitted by a
black body in thermal equilibrium at a given temperature T, when there is no net flow
of matter or energy between the body and its environment.

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4. Microwave Remote Sensing:

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The microwave energy recorded by a passive sensor can be emitted by the
atmosphere (1), reflected from the surface (2), emitted from the surface (3), or transmitted
from the subsurface (4). Because the wavelengths are so long, the energy available is quite
small compared to optical wavelengths. Thus, the fields of view must be large to detect
enough energy to record a signal. Most passive microwave sensors are therefore characterized
by low spatial resolution.
Applications of passive microwave remote sensing include meteorology, hydrology,
and oceanography. By looking "at", or "through" the atmosphere, depending on the
wavelength, meteorologists can use passive microwaves to measure atmospheric profiles and
to determine water and ozone content in the atmosphere. Hydrologists use passive
microwaves to measure soil moisture since microwave emission is influenced by moisture
content. Oceanographic applications include mapping sea ice, currents, and surface winds as
well as detection of pollutants, such as oil slicks.

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5. Radar Remote Sensing:

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6. Satellite Remote Sensing

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7. Airborne Remote Sensing:

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8. Acoustic and near- acoustic remote sensing

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Atmospheric Constituents

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Interaction with atmosphere

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Atmospheric window for various wavelength of EMR

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Figure is a generalized diagram showing relative radiation transmission of
different wavelength. Grey zones marked in Fig. show the minimal passage of
incoming and/ or outgoing radiation whereas white areas denote atmospheric
windows, in which the radiation does not interact much with air molecules and
hence, is not absorbed. Most remote sensing instrument on air or space
platforms operate in one or more these windows by making their measurements
with detectors tuned to specific frequencies (wavelength) that pass through the
atmosphere. However, some sensors, especially those on meteorological
satellite, directly measure absorption phenomenon, such as those associated
with carbon dioxide and other gaseous molecules.

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iv. Raman Scattering: Raman scattering is caused by atmospheric
particles, which are larger, smaller, or equal, to that of wavelength of the
radiation being sensed. The atmospheric particles may be gaseous molecules,
water droplets, fumes, or dust particles. The EMR has an elastic collision with
the atmospheric particles, which results in either loss or gain of energy and
thus an increase or decrease in wavelength.
The effect was discovered in 1928 by C. V. Raman and his student K. S.
Krishnan in liquids, and independently by Grigory Landsberg and Leonid
Mandelstam in crystals

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❖ Absorption is the process by which radiant energy is absorbed and converted
into other forms of energy. The absorption of the incident radiant energy may
take place in the atmosphere and on the terrain. An absorption band is a range
of wavelength (or frequencies) in the electromagnetic spectrum within which
radiant energy is absorbed by a substances.

64. 4. Refraction: When EMR encounters substances of different densities,
like air and water, refraction takes place. Refraction refer to bending of light when
it passes from one medium to another.
Refraction occurs because the media are of different densities and the
speed of EMR is different in each. The index of refraction (n) is a measure of the
optical density of a substances. This index is the ratio of the speed of light in a
vacuum, c (3X108 m/s), to the speed of light in a substances such as the
atmosphere or water, Cn
n= c/Cn
The speed of light in a substances can never reach the speed of light in
a vacuum. Therefore, its index of refraction must always be greater than 1. For
example the index of refraction for the atmosphere is 1.0002926.
Within the atmosphere there is a continuous movements of air. An
effect produced by the movement of masses of air with different refractive
indices is called atmospheric shimmer. The effect of shimmer can be most
easily detected in the twinkling of stars. Shimmer results in blurring on
remotely sensed images.

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Reflection: Reflection is the process whereby radiation ‘bounces off’ an
object like the top of a cloud, a water body, or the terrestrial earth. Reflection
differs from scattering in that the direction associated with scattering is
unpredictable but in case of reflection it is predictable. Reflection exhibits
fundamental characteristics that are important in the remote sensing.
First, the incident radiation, the reflected radiation and a vertical to the
surface from which the angles of incident and reflection are measured all lie in
the same plane. Second, the angle of incidence and the angle of reflection are
approximately equal.
A considerable amount of incident radiation flux from the sun is
reflected from the top of clouds and other materials in the atmosphere. This
results in recording of some extra amount of energy by the sensor in addition to
the reflected energy from the terrain (target). Blurred image and appearance of
cloud on the imagery are the main problems associated with atmospheric
reflection.

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