Transcript What is Remote sensing?

Dated :14/10/14
Lecture# 1 P-II
Subject
Database Management System &
Applications of Remote sensing and GIS
Topic
Concept of Remote Sensing
Consult Lectures 1,2 & 3 of Part-I for this topic
Presented by
Rehana Jamal
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What is Remote sensing?
Remote sensing is a
technique of
collecting
information from a
distance
OR
Remotely sensed data
The data collected
from a distance
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Definitions of Remote Sensing
“Remote Sensing (RS) is the science
and art of acquiring information
about material objects, area, or
phenomenon, without coming into
physical contact with the objects,
areas, or phenomenon under
investigation “
OR
“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”
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Characteristics of Electromagnetic radiation
Electromagnetic Energy can be modelled in two ways
i. By waves ii. By Photons(Energy bearing particles)
Electromagnetic waves consist of a combination of oscillating
electrical and magnetic fields, perpendicular to each other.
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Characteristics of Electromagnetic radiation
It can travel through empty space.
The speed of light is constant in space.
A wavelength: Distance between crests or troughs through visible light
Velocity: 186,000 miles per second or300,000 kilometers per second or
299,790,000m/s or 3*108 m/s
Amplitude: The amplitude of electromagnetic waves relates to its intensity or
brightness(as in the case of visible light)
Frequency:
•The number of crests of the waves that pass by a point per second.
•Measured in units of hertz(Hz)
•1 hertz = 1 wave crest/second
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/ Crest
Velocity of light, c
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Relation between the speed of light (c),
wavelength ( ), and frequency (f or V ):
f
or
V = c/
Thus, there is an inverse relationship between wavelength and frequency
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Relation between the speed of light (c),
wavelength ( ), and frequency (f or V ):
Thus (frequency [f/V] * wavelength[lambda]) is equal to a constant (c)
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Sources of electromagnetic radiation

Sources of long wavelengths

Sources of visible light

Sources of short wavelength

Detectors of electromagnetic radiation
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Note the trends: bluer light has shorter wavelength, higher frequency, and more
energy. Redder light has longer wavelength, lower frequency, and less energy.
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The unit of length chosen to describe a particular wavelength is
typically dependent on the type of electromagnetic radiation
Unit
Symbol
Length (m)
Type of Radiation
Angstrom
Å
10-10
X-ray
Nanometer
nm
10-9
UV, visible
Micrometer
µm
10-6
Infrared
Millimeter
mm
10-3
Infrared
Centimeter
cm
10-2
Microwave
Meter
m
1
TV, radio
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Types of Energy Resources
In respect to the type of Energy Resources:
Passive Remote Sensing: Makes use of sensors that detect the
reflected or emitted electro-magnetic radiation from natural sources.
Active remote Sensing: Makes use of sensors that detect reflected
responses from objects that are irradiated from artificially-generated
energy sources, such as radar.
In respect to Wavelength Regions:
Visible and Reflective Infrared Remote Sensing.
Thermal Infrared Remote Sensing.
Microwave Remote Sensing.
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In respect to the type of Energy Resources
Passive Remote Sensing
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In respect to the type of Energy Resources
Passive Remote Sensing
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In respect to the type of Energy Resources:
Active Passive remote Sensing
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Wavelength regions of electro-magnetic radiation
Electro-Magnetic Spectrum (EMS)
Remote Sensing Technology makes use of the wide range of Electro-Magnetic
Spectrum (EMS) from a very short wave "Gamma Ray" to a very long 'Radio
Wave'.
Wavelength regions of electro-magnetic radiation have different names
ranging from Gamma ray, X-ray, Ultraviolet (UV), Visible light, Infrared (IR)
to Radio Wave, in order from the shorter wavelengths to the longer
wavelengths.
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Electromagnetic spectrum
Definition: “The range of wavelengths for electromagnetic waves--from the
very long to the very short--is called the Electromagnetic Spectrum”. It includes
following wavelengths bands:
•Radio and TV waves are the longest usable waves, having a wavelength of 1
mile (1.5 kilometer) or more.
•Microwaves are used in telecommunication as well as for cooking food.
•Infrared waves are barely visible. They are the deep red rays you get from a
heat lamp.
•Visible light waves are the radiation you can see with your eyes. Their
wavelengths are in the range of 1/1000 centimeter.
•Ultraviolet rays are what give you sunburn and are used in "black lights" that
make object glow.
•X-rays go through the body and are used for medical purposes.
•Gamma rays are dangerous rays coming from nuclear reactors and atomic
bombs. They have the shortest wavelength in the electromagnetic spectrum of
about 1/10,000,000 centimeter.
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Name
Wavelength(mm)
Optical wavelength
Reflective portion
(i) Visible
(ii) Near IR
(iii) Middle IR
Far IR (Thermal, Emissive)
0.30-15.0
0.38-3.00
0.38-0.72
0.72-1.30
1.30-3.00
7.00-15.0
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In respect to Wavelength Regions
Visible and Reflective Infrared Remote Sensing
Thermal Infrared Remote Sensing
Microwave Remote Sensing
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(1mm)
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Summary
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Energy interactions in the atmosphere
Fundamental interactions in the atmosphere
Source of energy
Sun

Absorption

Transmission

Scattering
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Fig.1
Absorbed
Incoming solar
radiation 100%
Total atmospheric absorption 17 %
Scattered/Reflected
Total scattering/reflection 30% (albedo)
14 % By
atmospheric
components
5% By dust
25% By clouds
47%
3% By clouds
Clouds
Clouds
Direct
radiation
31%
22%
Diffuse
radiation
Earth’s surface
Fig. 2 Energy interactions
in the atmosphere
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Clouds
Energy interactions in the atmosphere & on the land
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Fig.3
Efficient absorbers of solar radiation
in the atmosphere



Ozone(O3)

Water vapour(H2O)

Carbon dioxide(CO2)
Electromagnetic spectrum between 0-22um is useless for
remote sensing
Only Wavelength regions out side the main absorption
bands of the atmospheric gases are useful for remote & these
regions are called “atmospheric transmission windows”
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“Atmospheric transmission windows”
Fig.5
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Fig.6
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“Atmospheric transmission windows”
A window in the visible & reflected infrared region(0.4-2um)
Three windows in the thermal infrared region
(Two narrow windows around 3 & 5um & Third relatively broad
window from 8 to 14 um)
Frequency(Hz)
ELECTROMAGNETIC
SPECTRUM
Fig.4
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AM
Radar
Far IR
Thermal IR
Near IR
Wavelength
Atmospheric Scattering
Amount of scattering depends on following factors:



wavelength of the radiation
the amount of particles & gases
radiation distance
Types of scattering
Rayleigh scattering (Particle size < wavelength)
Mie scattering
( Particle size = wavelength)
Non-selective scattering
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(Particle size > wavelength)
Energy interactions with the Earth’s surface
In remote sensing applications, Land & Water have different
surface characteristics
Energy interactions: When electro-magnetic energy is incident on
any given earth surface feature, three fundamental energy
interactions with the features are possible:1.Reflection , 2.Absorption , 3.Transmission
Fig.7
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Two types of Reflection
Specular reflection (mirror like reflection from smooth surface)
Diffuse reflection (reflection from rough surface)
Fig.8
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Fig.9
Fig.10
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Irradiance & radiance

Sun
Energy reaching the
surface is called irradiance.
Earth’s surface

Energy reflected by the surface is
called radiance
Earth’s surface

The density of radiation incident on a given surface usually
expressed in watts per square centimeter or square meter.
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Summary
Remote sensing is a technique of collecting information from a distance
Characteristics of Electromagnetic radiation




A wavelength
Velocity
Amplitude
Frequency
Electromagnetic Spectrum
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Summary
Interactions between Matter & Electromagnetic radiation
Energy interactions in the atmosphere:
Absorption, Transmission, Scattering
Atmospheric absorption
Direct radiance
Reflected and scattered by cloud
Reflected and scattered by dust
17%
31 %
47 %
5%
Efficient absorbers of solar radiation in the atmosphere
Ozone(O3), Water vapour(H2O), Carbon dioxide(CO2
Types of scattering
Rayleigh scattering (Particle size < wavelength)
Mie scattering ( Particle size = wavelength)
Non-selective scattering (Particle size > wavelength
Types of Reflection
Specular reflection, Diffuse reflection
Percentage of spectral reflectance
Vegetation:
Soil :
Water:
50%
30-40%
10%
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References
•
www.google.com
•
www.wikipedia.com
•
Principles of Remote sensing
•
edited by Lucas L.E. Janssen
•
Remote sensing and image interpretation by Thomas M.Lillesand
•
University Practical Geography by M. Iftikhar Akram Ch.
•
http://www.answers.com/topic/specular/-reflection
•
http://hyperphysics.phyastr.gsu.edu/hbase/mod3.html
•
http://hosting.soonet.ca/eliris/remotesensing/bl130lec3.html
•
http://www.cps-amu.org/sf/notes/m1r-1-8.htm
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Possible Exam Questions
Q1. Define the following:
 Visible spectram
 Infrared wavelength region
 Optical wavelength range
 Radio wave band
Q2.Differentiate the Passive remote sensing and Active remote
sensing.
5 Marks
Q3.Define Electromagnetic spectrum. Describe in detail the all
wavelength regions of electromagnetic spectrum. 15 Marks
Q5.Write a not on EM spectrum.
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5 Marks
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