unit iv remote sensing

3/10/2016

1

Remote Sensing & its Applications in Civil

Engineering

Akshay Jain

www.akshayjain.co.in

by

What is Remote Sensing

Remote sensing is the science (and to

some extent, art) of acquiring

information about the Earth's surface

without actually being in contact with it.

This is done by sensing and recording

reflected or emitted electromagnetic

energy and processing, analyzing, and

applying that information.

Since our birth, Remote sensing activities have

been carried out by each one of us

listening music (Activity) – ears (sound energy) - Head (Sensor)

Reading book (Activity) – eyes (light energy) - Head (Sensor)

Nervous system carries information to brain

Brain (interpreter) identify the object

sensors are not in contact with object

Measurement of Temperature with thermometer is

in-situ measurement

http://www.akshayjain.co.in/

3/10/2016

2

Elements of RS

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)

Elements of RS

Energy Source or Illumination (A)

The first requirement for remote sensing is to have

an energy source which illuminates or provides

electromagnetic energy to the target of interest.

Radiation and the Atmosphere (B)

As the energy travels from its source to the target, itwill come in contact with and interact with theatmosphere it passes through. This interaction maytake place a second time as the energy travels fromthe target to the sensor.

Interaction with the Target (C)

once the energy makes its way to the target through the atmosphere, it interacts with the target depending on the properties of both the target and the radiation.

Recording of Energy by the Sensor (D)

after the energy has been scattered by, or emitted from the target, we require a sensor (remote - not in contact with the target) to collect and record the electromagnetic radiation.

Elements of RS

3/10/2016

3

Transmission, Reception, and Processing (E)

The energy recorded by the sensor has to be

transmitted, often in electronic form, to a receiving and

processing station where the data are processed into an

image (hardcopy and/or digital).

Interpretation and Analysis (F)

The processed image is interpreted, visually and/or

digitally or electronically, to extract information about

the target which was illuminated.

Elements of RS

Application (G)

The final element of the remote sensing process is

achieved when we apply the information we have

been able to extract from the imagery about the

target in order to better understand it, reveal some

new information, or assist in solving a particular

problem.

Elements of RS

Different Remote Sensing Systems

Passive system

The source of the object illumination is independent of the sensor and it is a natural source.

Passive sensors used when naturally energy is available. during the time when the sun is illuminating the Earth.

No reflected energy available

from the sun at night.

3/10/2016

4

Active Remote Sensing

Active system

Own energy source of illumination

sensor emits radiation

which is directed toward the target to be investigated. The radiation reflected from that target is detected and measured by the sensor

Ability to obtain measurements anytime, day or season.

Active sensors can be used for examining wavelengths that are not sufficiently provided by the sun, such as microwaves,

Active systems require the generation of a fairly large amount of energy to adequately illuminate targets.

Laser Fluorosensor, Synthetic Aperture Radar (SAR).

Electromagnetic Radiation

Energy source to illuminate the target

This energy is in the form of electromagnetic radiation.

Energy Source

All electromagnetic radiation hasfundamental properties and behaves inpredictable ways according to the basics ofwave theory.

Electromagnetic radiation consists of anelectrical field (E) which varies in magnitudein a direction perpendicular to the directionin which the radiation is traveling.

Magnetic field (M) oriented at right angles tothe electrical field. Both these fields travel atthe speed of light (c).

3/10/2016

5

Electric Field

Magnetic FieldDirection of

propagation

- Wavelength(λ)

- Frequency

Wavelength is the length ofone wave cycle, which canbe measured as the distancebetween successive wavecrest

Wavelength usually measuredin metres or some factor ofmetres such as nanometres(nm, 10-9 m) or micrometres(μm, 10-6 metres) orcentimetres (cm, 10-2metres).

Frequency 3 Hzt = 0 sec

t = 1sec

Two important characteristics of EMR

Frequency refers to the number of cycles of a wavepassing a fixed point per unit of time. Frequency isnormally measured in hertz (Hz), equivalent to onecycle per second, and various multiples of hertz.

Wavelength and Frequency are related by thefollowing formula:Wavelength and frequency arerelated by the following formula:

Wavelength and Frequency are inversely proportional to each other

3/10/2016

6

Electromagnetic Spectrum

Ultraviolet

Visible - 0.4 to 0.7 mm

Infrared (IR) - 0.7 mm to 100

mm

Reflected IR - 0.7 mm to 3.0

mm

Thermal IR - 3.0 mm to 100

mm

Microwave Region - 1 mm to

1 m

Visible Spectrum

Called Light waves

Occupies only small portion of electromagnetic

spectrum

Wavelength between 0.4 μm to 0.7 μm

Optical Infrared Region (OIR)

Visible 0.4 to 0.7 μm

Near Infrared 0.7 to 1.5 μm

Shortwave Infrared 1.5 to 3 μm

Mid-wave infrared 3 to 8 μm

Long wave Infrared (Thermal Infrared-TIR) 8 to 15 μm

Far Infrared (FIR) Beyond 15 μm

Marginal Differences in the range of wavelength in different literature

3/10/2016

7

Sun and Atmosphere

Before radiation used for remote sensingreaches the Earth's surface it has to travelthrough some distance of the Earth'satmosphere.

Particles(Aerosols, dust particles) andgases (CO2

,H2O, Vapour,O3) in theatmosphere can affect the incoming lightand radiation. These effects are causedby the mechanisms of scattering andabsorption.

Scattering

Scattering occurs when

suspended particles or large

gas molecules present in the

atmosphere interact

Cause the electromagnetic

radiation to be redirected from

its original path.

Depends on several factors

Wavelength of the radiation the

Abundance of particles or gases

Distance the radiation travels

through the atmosphere

Types of ScatteringRayleigh Scattering

Occurs when particles are very small compared to thewavelength of the radiation.

Particles such as small dust or nitrogen and oxygenmolecules.

Shorter wavelengths of energy to be scattered muchmore than longer wavelengths.

Rayleigh scattering is the dominant scatteringmechanism in the upper atmosphere.

Sky appears "blue" during the day is because of thisphenomenon. Shorter wavelengths (i.e. blue) of thevisible spectrum are scattered more than the other(longer) visible wavelengths.

Rayleigh Scattering is the most important type ofscattering and cause high path radiance at the blue-endof spectrum.

It leads to haze on images and photographs, whichresults in contrast and unsharp pictures

Effects can be reduced by the filters to eliminate shorterwavelength radiation

3/10/2016

8

Mie scattering occurs when the particles (Spherical) arejust about the same size or larger than the wavelength ofthe radiation

Dust, smoke and water vapour are common causes ofMie scattering

Mie scattering occurs in the lower altitude of theatmosphere

Mie Scattering influences the entire spectral region fromNear UV to Near IR

It has greater affect on larger wavelengths than Raleighscattering

Mie Scattering depends on factors such as ratio of thesize of scatterer particle to the wave length incidence.

Dominates when cloud conditions are overcast

Nonselective scattering

Occurs when the particles are much largerthan the wavelength of the radiation.

Due to water droplets and large dustparticles

Nonselective scattering gets its name fromthe fact that all wavelengths are scatteredabout equally

This type of scattering causes fog andclouds to appear white to our eyes

Absorption

Absorption

This phenomenon causes molecules in the atmosphere toabsorb energy at various wavelengths.

Ozone, carbon dioxide, and water vapour are the three mainatmospheric constituents which absorb radiation.

Ozone serves to absorb the harmful UV radiation from thesun.

Carbon Dioxide tends to absorb radiation strongly in the farinfrared portion of the spectrum - that area associated withthermal heating - which serves to trap this heat inside theatmosphere.

Water vapour in the atmosphere absorbs much of theincoming longwave infrared and shortwave microwaveradiation (between 22µm and 1m).

water vapour in the lower atmosphere varies greatly fromlocation to location and at different times of the year.

For remote sensing, area of spectrum which is very muchuseful is visible region because atmospheric absorption isless in this area

3/10/2016

9

Those areas of the spectrum which are notseverely influenced by atmosphericabsorption and thus, are useful to remotesensors, are called atmosphericwindows

Atmospheric Emission

Atmosphere emits EM radiation due to its thermal

state ( All bodies above absolute temperature,

emits EM radiation)

Path Radiance : The part of signal emanating from

the atmosphere is called path radiance

Path radiance reduce the contrast of the image

generated by the sensor, hence visual sharpness of

the image will reduce (Radiometric Error)

Energy Interaction Mechanism on the Ground

Radiation that is not absorbed or scattered inthe atmosphere can reach and interact withthe Earth's surface.

EM Energy incident (Eiλ) on the earth surfacemay be absorbed (Eaλ); transmitted (E tλ); andreflected (E rλ).

Eiλ = Eaλ + E tλ + E rλ

Absorption ,Transmission and Reflection arediffer for different objects at differentwavelength and condition

We are interested in reflected energy from thetarget

specular reflection

Diffuse reflection

semi-diffused reflection

3/10/2016

10

Specular or Mirror-like reflection

smooth surface, where all or almost all of the energy is

directed away from the surface in a single direction.

Diffuse reflection

Rough surface, where the energy is reflected almost

uniformly in all directions.

Most earth surface features lie somewhere between

perfectly specular or perfectly diffuse reflectors.

Whether a particular target reflects specularly or

diffusely, or somewhere in between, depends on the

surface roughness of the feature in comparison to the

wavelength of the incoming radiation.

If the wavelengths are much smaller than the surface

variations or the particle sizes that make up the

surface, diffuse reflection will dominate.

For example, fine-grained sand would appear fairly

smooth to long wavelength microwaves but would

appear quite rough to the visible wavelengths.

SPECTRAL REFLECTION

DIFFUSED REFLECTION

Leaves

A chemical compound in leaves called chlorophyll

strongly absorbs radiation in the red and blue

wavelengths but reflects green wavelengths.

Leaves appear "greenest" to us in the summer, when

chlorophyll content is at its maximum.

In autumn, there is less chlorophyll in the leaves, so

there is less absorption and proportionately more

reflection of the red wavelengths, making the leaves

appear red or yellow (yellow is a combination of red

and green wavelengths

The internal structure of healthy leaves act as

excellent diffuse reflectors of near-infrared

wavelengths.

If our eyes were sensitive to near-infrared, trees

would appear extremely bright to us at these

wavelengths. In fact, measuring and monitoring the

near-IR reflectance is one way that scientists can

determine how healthy (or unhealthy) vegetation may

be.

Water: Longer wavelength visible and near infrared

radiation is absorbed more by water than shorter visible

wavelengths. Thus water typically looks blue or blue-green

due to stronger reflectance at these shorter wavelengths,

and darker if viewed at red or near infrared wavelengths.

If there is suspended sediment present in the upper layersof the water body, then this will allow better reflectivity and

a brighter appearance of the water. The apparent colour of

the water will show a slight shift to longer wavelengths.

Suspended sediment (S) can be easily confused with

shallow (but clear) water, since these two phenomena

appear very similar.

Chlorophyll in algae absorbs more of the blue

wavelengths and reflects the green, making the water

appear more green in colour when algae is present.

The topography of the water surface (rough, smooth,

floating materials, etc.) can also lead to complications for

water-related interpretation due to potential problems ofspecular reflection and other influences on colour and

brightness.

3/10/2016

11

Single Channel/Multi Channel Concept

Information from a narrow wavelength range isgathered and stored in a channel (band)

We can combine and display channels ofinformation digitally using the three primary colours

single channel or range of wavelengths, we areactually displaying that channel through all threeprimary colours. Because the brightness level ofeach pixel is the same for each primary colour, theycombine to form a black and white image, showing

various shades of gray from black to white.

When we display more than one channel each as adifferent primary colour, then the brightness levelsmay be different for each channel/primary colourcombination and they will combine to form a colourimage.

Single Channel

Multi Channel

Sensor and Platform

Platform where the

sensors are placed

Sensors may be

Ground based

Aircraft

Space shuttle

Satellites

Sun Synchronous

Geo Stationary

3/10/2016

12

Resolution, Pixel Size and Scale

Spatial resolution of the sensor and refersto the size of the smallest possible featurethat can be detected.

Spatial resolution of passive sensorsdepends primarily on their InstantaneousField of View (IFOV).

The IFOV is the angular cone of visibility ofthe sensor (A) and

Determines the area on the Earth's surfacewhich is "seen" from a given altitude at oneparticular moment in time (B).

The size of the area viewed is determinedby multiplying the IFOV by the distancefrom the ground to the sensor (C)

Data Resolution

Spatial resolution - size of the smallest

possible feature that can be detected

Spectral resolution - Ability of a sensor

to define fine wavelength intervals

Radiometric resolution - Ability to

discriminate very slight differences in

energy

Temporal resolution

SATELLITE SYSTEMS

LANDSAT

SPOT

IRS

3/10/2016

13

Indian Remote Sensing satellite

(IRS)

Earth Observation satellites, mostly built,

launched and maintained by Indian Space

Research Organisation (ISRO)

Father of Space Technology in India

Dr.Vikarmbhai Sarabhai

National Natural Resources Management

System (NNRMS) for which the Department of

Space (DOS) is nodal agency

Bhaskara 1 satellites launched in 1979

Bhaskara 2 satellites launched in 1981

largest constellation of remote sensing satellites for

civilian use in operation today

IRS

Is

Sun Synchronous and Provides variety of

spatial, spectral and temporal resolutions

IRS-1D,

OCEANSAT-1

Technology Experiment Satellite (TES)

RESOURCESAT-1

CARTOSAT-1, CARTOSAT-2

CARTOSAT-2A

IMS-1

IRS Satellites are

3/10/2016

14

Serial

No.

Satellite Date of Launch Launch Vehicle Status

1 IRS 1A 17 March 1988 Vostok, USSR Mission Completed

2 IRS 1B 29 August 1991 Vostok, USSR Mission Completed

3 IRS P1 (also IE) 20 September 1993 PSLV-D1 Crashed, due to

launch failure of

PSLV

4 IRS P2 15 October 1994 PSLV-D2 Mission Completed

5 IRS 1C 28 December 1995 Molniya, Russia Mission Completed

6 IRS P3 21 March 1996 PSLV-D3 Mission Completed

7 IRS 1D 29 September 1997 PSLV-C1 In service

8 IRS P4 (Oceansat-1) 27 May 1999 PSLV-C2 In service

9 Technology Experiment

Satellite (TES)

22 October 2001 PSLV-C3 In service

10 IRS P6 (Resourcesat 1) 17 October 2003 PSLV-C5 In service

11 IRS P5 (Cartosat 1) 5 May 2005 PSLV-C6 In service

12 Cartosat 2 (IRS P7) 10 January 2007 PSLV-C7 In service

13 Cartosat 2A (IRS P7) 28 April 2008 PSLV-C9 In service

14 IMS 1 (IRS P7)

Integrated Mission for

Sustainable Development

28 April 2008 PSLV-C9 In service

Data Acquisition and Analysis

National Remote Sensing Agency (NRSA)

Hyderabad

Reception

Archival

Processing

Dissemination

IRS Data applications

Preharvest crop area and production estimation of major crops.

Drought monitoring and assessment based on vegetation condition.

Flood risk zone mapping and flood damage assessment.

Hydro-geomorphological maps for locating underground water resources for drilling well.

Irrigation command area status monitoring

Snow-melt run-off estimates for planning water use in down stream projects

Land use and land cover mapping

Urban planning

Forest survey

Wetland mapping

Environmental impact analysis

Mineral Prospecting

Coastal studies

Integrated Mission for Sustainable Development (initiated in 1992) for generating locale-specific prescriptions for integrated land and water resources development in 174 districts

3/10/2016

15

REMOTE SENSING DATA

ANALYSIS

FCC OF ROORKEE AREA IRS LISS III

DATA

IKONOS DATA OF ROORKEE DATA

3/10/2016

16

PROCESSING & ANALYSIS

INTERPRETATION

Visual - Human based

Digital - Computer assisted

COMPARISON

VISUAL ANALYSIS

Single band or as FCC

Slow

Analyst Bias

Subjective

DIGITAL ANALYSIS

Multi Image

Fast with many options

Free of Analyst bias

Objective

Elements of Image Interpretation

Primary Elements

Black and White Tone

Color

Spatial Arrangement of Tone & Color

Size

Shape

Texture

Pattern

Based on Analysis of Primary

Elements

Height

Shadow

Contextual Elements

Site

Association

3/10/2016

17

Elements of Visual Interpretation

Tone - relative brightness or colour of objects in

an image.

.

Generally, tone is the

fundamental element for

distinguishing between different

targets or features.

Variations in tone also allows the

elements of shape, texture, and

pattern of objects to be

distinguished


Shape - general form, structure, or outline of

individual objects

Shape can be a very distinctive clue

for interpretation.

Straight edge shapes typically

represent urban or agricultural (field)

targets.

Natural features, such as forest edges,

are generally more irregular in shape,

except where man has created a road

or clear cuts.


Size - to assess the size of a target

A quick approximation of target

size can direct interpretation to

an appropriate result more

quickly.

Large buildings factories or

warehouses would suggest

commercial property,

Small buildings would indicate

residential use.

3/10/2016

18


Pattern - spatial arrangement of objects

Spatial arrangement of surface

features

Similar features under similar

condition reflects similar pattern

Linear – road, railway, canal

Nonlinear- Stream, River, Creeks

Clustered – Settlement

Dispersed – forest blanks, salt

affected patches

Regular pattern - Orchard


Texture - arrangement and frequency of tonal

variation Rough textures would consist of a

mottled tone where the grey levels

change abruptly in a small area,

whereas smooth textures would have

very little tonal variation.

Smooth textures are most often the

result of uniform, even surfaces,

such as fields or grasslands.


Shadow - provides an idea of the profile and

relative height of a target or targets which

may make identification easier

shadows can also reduce or eliminate

interpretation in their area of

influence

•useful for enhancing or identifying

topography and landforms

3/10/2016

19

Location

Geographical Site and Location of object

Building near sea – Light House

Salt affected land – Near sea

Glacier – mountain peaks


Association - relationship between other

recognizable objects

a lake is associated with boats, a

marina, and adjacent recreational

land.

Canal with agricultural field

Marsh or swamp with flood plain

or tidal flats

DIGITAL IMAGE PROCESSING

3/10/2016

20

Preprocessing

When remotely sensed data is received from the

imaging sensors on the satellite platforms it contains

flaws and deficiencies.

Pre-processing refers to those operations that are

preliminary to the main analysis.

1. Radiometric Corrections

2. Geometric Corrections

3. Atmospheric Correction

4. Feature Extraction

Radiometric Corrections

Radiometric Corrections are carried

out when an image data is recorded

by the sensors they contain errors in

the measured brightness values of

the pixels. These errors are referred

as radiometric errors.

Geometric Corrections

Raw digital images often contain serious geometricaldistortions that arise from earth curvature, platform motion,relief displacement, non-linearity in scanning motion.

3/10/2016

21

Atmospheric Corrections

The path radiation coming from the

sun to the ground pixel and then

being reflected to the sensor is

effected by atmosphere.

In this on going process, absorption

by atmospheric molecules takes

place that converts incoming energy

into heat.

In particular, molecules of oxygen,

carbon-di-oxide, ozone and water

attenuate the radiation very strongly

in certain wavelengths.

Scattering by these atmospheric

particles is also the dominant

mechanism that leads to radiometric

distortion in image data.

Image Classification and Analysis

Spectral pattern recognition

Digital image classification uses the spectral

information represented by the digital numbers in

one or more spectral bands, and attempts to

classify each individual pixel based on this

spectral information

The resulting classified image is comprised of a

mosaic of pixels, each of which belong to a

particular theme, and is essentially a thematic "map"

of the original image.

Common classification procedures

Supervised classification

Unsupervised classification

3/10/2016

22

Comparison

Supervised classification

Training areas

the analyst identifies in the

imagery homogeneous

representative samples of the

different surface cover types

To determine the

numerical "signatures” Once the computer has

determined the signatures for

each class, each pixel in the

image is compared to these

signatures and labeled as the

class it most closely "resembles"

digitally

Unsupervised classification

reverse of supervised classification

Spectral classes are grouped first

Then matched to information classes

the analyst specifies how many

groups or clusters

It is iterative in nature

not completely without human

intervention

3/10/2016

23

Applications of RS in Civil

Engineering

Self Study