introduction to remote sensing

REMOTE SENSING

D.UDAY KUMAR, LecturerNBKRIST,

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 = σΤᶺ4M = Total radiant existence of material, Watts/mᶺ2σ = Stephan boltzmann’s constant 5.6697x10ᶺ-8 W/mᶺ2/˚KT = Temperature in ˚K


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



E= Black body spectral radiance measued in w/mᶺ2/mh= Planck’s constantK= Boltzmann’s constantc= speed of lighte= base of the logarithmλ= wave length in ‘m’T= temperature in ˚K


Wien’s displacement law λmax = b/Tλmax = wave length of maximum emitted energy

measured in, μm b = Wien's displacement constantT = Temperature in ˚K


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

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 EARTH’S ATMOSPHERE

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. Reflection2. 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

ENERGY INTERACTIONS WITH 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

ENERGY INTERACTIONS WITH WATER

ENERGY INTERACTIONS WITH WATER

Date post:	16-Aug-2015
Category:	Engineering
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introduction to remote sensing

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