Introduction to Remote Sensing

REMOTE SENSING
D.UDAY KUMAR, Lecturer
NBKRIST,
Vidyanagar

INTRODUCTION TO REMOTE
SENSING
Definition :
Remote sensing is an art
and science of obtaining
information about an
object or feature without
physically coming in
contact with that object
or feature

APPLICATION OF REMOTE SENSING
 Flood estimation

 Earthquake Estimation

 Weather Maps

 Crop Yielding
 Tsunamis
 Forest Fires
 Regional Planning
 Surveying in Inaccessible Areas
 Flood and Drought Warnings

HISTORY OF REMOTE SENSING :
 Remote sensing starts
with the invention of
camera more than 150
years ago(1840s)
 The idea and practice
looking down the earth
surface emerged in
1840s cameras secured
to tethered balloon

 Famed pigeons are used
for remote sensing

 In the first world war
cameras mounted on
airplanes are used to
provide images of large
surface areas

 In 1960s and 1970s primary platform changed to
satellites

 Sensors become available to record the earth surface
in several bands what human’s eye couldn’t see

Starts in 1960s
First Indian satellites
• Aryabhata (19-April-1975 ) launched
in LEO by USSR rocket
• Bhaskara I & II carrying two TV
cameras
• Rohini siries (experimental)
INDIAN REMTE SENSING

First Indian Remote Sensing Satellites
 IRS-1A (17-March-1988), 904 km
 IRS-1B (29-August-1991)
Both carrying
LISS-1A (Resolution 72.5 m)
LISS-2A,LISS-2B (Resolution 36.25 m)
 IRS-1C (1995), 817 km
 IRS-1D (1997)

Ground Control Stations
 Located at Bangalore( tracking and
monitoring)
 National Remote Sensing Centre
located at Hyderabad (Balanagar
&Shadnagar) to process data

Various Forms Of Collected Data
 Acoustic Wave Distribution (Ion based)
 Force Distribution (Force based)
 Electromagnetic Energy (Wavelength
based) and
REMOTE SENSING DEALS WITH DATA
COLLECTED BY ELECTROMAGNETIC
ENERGY
PHYSICS OF REMOTE SENSING

 Combination of Electric
and Magnetic fields
both are mutually
perpendicular to each
other passes
perpendicular to the
light
 Travels with a speed of
light (3 x 10ᶺ8 m/sec)
ELECTROMAGNETIC ENERGY

ELECTROMAGNETIC RADIATION
 EMR is originated from billions of vibrating
electrons, atoms , and molecules which emits EMR
in unique combination of wave lengths
 All the objects above -273˚C (0˚K) Reflects, Emits
and Absorbs EMR
 Amount of EMR radiation depends on the
Temperature of the Object

Data Acquisition:
 Source of EM energy
 Propagation of EM energy through atmosphere
 Interaction of EM energy with earth surface features
 Re-transmission of the EM energy through
atmosphere
 Recording of the reflected EM energy by the sensing
systems
 Generation of the sensor data in pictorial or digital
form
GENERAL PROCESS OF REMOTE
SENSNG

Data Analysis:
 Interpretation and analysis of the generated data
 Generation of information products
 Users
GENERAL PROCESS OF REMOTE
SENSNG

BASIC WAVE THEORY
 EM Energy travels in a harmonic sinusoidal fashion
(3 x 10ᴧ8 m/sec)
 EM wave consists of two fluctuating fields

 wave length is defined as the distance between two
successive crests(λ)
 no of cycles of passing a fixed point in space is called
frequency
Waves obey the equation
c = νλ
ν = frequency
λ = wave length
BASIC WAVE THEORY

• It tells about how the EM
Energy interacts with
matter
• The smallest possible unit
is photon
• Each possesses a certain
quantity of energy
• Q = hc/λ
h = Planck’s constant
6.626x10ᶺ-34 J-sec
c = velocity of wave
λ = wave length
PARTICLE THEORY

ELECTROMAGNETIC SPECTRUM
Distribution of the continuum of radiant energy
can be plotted as a function of wavelength (or
frequency) and is known as the electromagnetic
radiation (EMR) spectrum

ENERGY SOURCES AND RADIATION
PRINCIPLES
• Primary source of energy that illuminates different
features on the earth surface is the Sun.
• Although the Sun produces electromagnetic
radiation in a wide range of wavelengths, the
amount of energy it produces is not uniform across
all wavelengths.
• Other than the solar radiation, the Earth and the
terrestrial objects also are the sources of
electromagnetic radiation. All matter at
temperature above absolute zero (0oK or -273˚C)
emits electromagnetic radiations continuously.

Stephan Boltzmann’s law
M = σΤᶺ4
M = Total radiant existence of material,
Watts/mᶺ2
σ = Stephan boltzmann’s constant
5.6697x10ᶺ-8 W/mᶺ2/˚K
T = Temperature in ˚K
PRINCIPLES

Black body Radiation:
A blackbody is a hypothetical, ideal radiator. It
absorbs and reemits the entire energy incident upon
it.
• No body in space is perfectly blackbody
• As the temperature increases, the peak shifts
towards the left. This is explained by the Wien’s
displacement law. It states that the dominant
wavelength at which a black body radiates “ λm ” is
inversely proportional to the absolute temperature
of the black body
PRINCIPLES

PRINCIPLES

E= Black body spectral radiance measued in w/mᶺ2/m
h= Planck’s constant
K= Boltzmann’s constant
c= speed of light
e= base of the logarithm
λ= wave length in ‘m’
T= temperature in ˚K
PRINCIPLES

Wien’s displacement law
λmax = b/T
λmax = wave length of maximum emitted energy
measured in, μm
b = Wien's displacement constant
T = Temperature in ˚K
PRINCIPLES

EARTH’S ATMOSPHERE
Composition Of The
Atmosphere
Atmosphere is the gaseous
envelop that surrounds the
Earth’s surface. Much of the
gases are concentrated
within the lower 100km of
the atmosphere. Only 3x10-
5 percent of the gases are
found above 100 km
(Gibbson, 2000).

Gaseous Composition of The Earth’s Atmosphere

The radiation from the
energy source passes
through some distance
of atmosphere before
being detected by the
remote sensor
ENERGY INTERACTIONS IN THE

SCATTERING :
Atmospheric scattering
is the process by which
small particles in the
atmosphere diffuse a
portion of the incident
radiation in all
directions

TYPES OF SCATTERING :
1. Rayleigh scattering
2. Mie scattering
3. Non-selective scattering

Rayleigh scattering :
This occurs when the
particles causing the
scattering are much
smaller in diameter
(less than one tenth)
than the wavelengths of
radiation interacting
with them.

Mie Scattering :
• which occurs when the wavelengths of the
energy is almost equal to the diameter of the
atmospheric particles
• longer wavelengths also get scattered compared
to Rayleigh scatter

Non-selective scattering :
• which occurs when the diameters of the
atmospheric particles are much larger
(approximately 10 times) than the wavelengths
being sensed
• This scattering is non-selective with respect to
wavelength since all visible and IR wavelengths get
scattered equally

ABSORBTION :
• Absorption is the process in which incident
energy is retained by particles in the
atmosphere at a given wavelength
• The most efficient absorbers of solar
radiation are water vapour, carbon dioxide, and
ozone

ATMOSPHERIC WINDOWS:
“The ranges of wavelength that are partially or
wholly transmitted through the atmosphere
are known as "atmospheric windows”

Sensor Selection For Remote Sensing
• The spectral sensitivity of the available sensors
• The available atmospheric windows in the spectral
range(s) considered. The spectral range of the sensor is
selected by considering the energy interactions with the
features under investigation.
• The source, magnitude, and spectral composition of the
energy available in the particular range.
• Multi Spectral Sensors sense simultaneously through
multiple, narrow wavelength ranges that can be located at
various points in visible through the thermal spectral
regions

Energy Interactions :
1. Reflection
2. Absorption
3. Transmission
ENERGY INTERACTIONS WITH
EARTH’S SURFACWE FEATURES

REFLECTION :
• Reflection is the process in which the incident energy is
redirected in such a way that the angle of incidence is
equal to the angle of reflection
• Electromagnetic energy is incident on the surface, it may
get reflected or scattered depending upon the
roughness of the surface relative to the wavelength of
the incident energy

Types Of Reflections:
Diffuse Reflection
• It occurs when the surface is smooth and flat
• A mirror-like or smooth reflection is obtained
where complete or nearly complete incident energy
is reflected in one direction
Specular Reflection
• It occurs when the surface is rough.
• The energy is reflected uniformly in all directions

Spectral Reflectance :
Spectral signature :

ENERGY INTERACTIONS WITH SOIL
• Some of the factors effecting soil reflectance are
moisture content, soil texture (proportion of
sand, silt, and clay), surface roughness, presence
of iron oxide and organic matter content
• water absorption bands at 1.4, 1.9, and 2.7 μm.
• coarse, sandy soils are usually well drained,
resulting in low moisture content and relatively
high reflectance

• Spectral reflectance curve for healthy green
vegetation exhibits the "peak-and-valley" c
• In general, healthy vegetations are very good
absorbers of electromagnetic energy in the visible
region configuration
• The absorption greatly reduces and reflection
increases in the red/infrared boundary near 0.7 μm
VEGITATION

• Water provides a semi-transparent medium for the
electromagnetic radiation. Thus the electromagnetic
radiations get reflected, transmitted or absorbed in
water
• Water in the liquid form shows high reflectance in
the visible region between 0.4μm and 0.6μm.
Wavelengths beyond 0.7μm are completely
absorbed. Thus clear water appears in darker tone
in the NIR image
WATER

WATER

Introduction to Remote Sensing

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Introduction to Remote Sensing