APPLICATION OF REMOTE SENSING AND

GEOGRAPHICAL INFORMATION SYSTEM IN

CIVIL ENGINEERING

Date:

INSTRUCTOR

DR. MOHSIN SIDDIQUE

ASSIST. PROFESSOR

DEPARTMENT OF CIVIL ENGINEERING

Electromagnetic (EM) Spectrum2

� The portion of the spectrum ofmore recent interest to remotesensing is the microwave regionfrom about 1mm to 1m.

� This covers the longest wavelengthsused for remote sensing.

� The shorter wavelengths haveproperties similar to the thermalinfrared region while the longerwavelengths approach thewavelengths used for radiobroadcasts.

� The remote sensing using

microwave spectrum is termed

as microwave sensing

Microwave Spectrum3

� Microwave remote sensing covers EM spectrum inthe range from approximately 1mm to 1m

� Because of their long wavelengths, compared tothe visible and infrared, microwaves have specialproperties that are important for remote sensing.

� Longer wavelength microwave radiation canpenetrate through cloud cover, haze, dust, andall but the heaviest rainfall as the longerwavelengths are not susceptible to atmosphericscattering which affects shorter opticalwavelengths.

� This property allows detection of microwaveenergy under almost all weather andenvironmental conditions so that data can becollected at any time

Microwave Remote Sensing4

Type of Microwave Remote Sensing5

�Passive RS�Natural (EMR from Sun)

RS using reflected solar radiation

RS using emitted terrestrial radiation

�Active RS

� Technological Assisted

Radiation

RS using senor’s transmitted radiation

� Passive microwave sensing is similar in concept to thermal remote sensing.

� All objects emit microwave energy of some magnitude, but the amounts aregenerally very small.

� A passive microwave sensor detects the naturally emitted microwave energywithin its field of view. This emitted energy is related to the temperature andmoisture properties of the emitting object or surface.

� Because the wavelengths are so long, the energy available is quite smallcompared to optical wavelengths. Thus, the fields of view must be large todetect enough energy to record a signal.

� Most passive microwave sensors are therefore characterized by low spatialresolution.

� Applications of passive microwave remote sensing include meteorology,hydrology, and oceanography

Passive microwave sensing6

� Active microwave sensors provide theirown source of microwave radiation toilluminate the target

� The most common form of imaging activemicrowave sensors is RADAR.

� RADAR is an acronym for RAdio

Detection And Ranging

� RADAR transmits a microwave (radio)signal towards the target and detects thebackscattered portion of the signal.

� The strength of the backscattered signalis measured to discriminate betweendifferent targets and the time delaybetween the transmitted and reflectedsignals determines the distance (or range)to the target

Active microwave sensing7

� A radar is essentially a ranging or distancemeasuring device.

� It consists fundamentally of a transmitter, areceiver, an antenna, and an electronics system toprocess and record the data.

� The transmitter generates successive short bursts (orpulses of microwave (A) at regular intervals whichare focused by the antenna into a beam (B). Theradar beam illuminates the surface obliquely at aright angle to the motion of the platform.

� The antenna receives a portion of the transmittedenergy reflected (or backscattered) from variousobjects within the illuminated beam (C).

How Radar Works

By measuring the time delay between the transmission of a pulse and the reception of the backscattered "echo" from different targets, their distance from the radar and thus their location can be determined

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How Radar Works

Pulse radar: The round-trip time for the radar pulse

to get to the target and return is measured. The

distance is proportional to this time.

Continuous wave (CW) radar

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Fundamental Radar Equation10

� Ka, K, and Ku bands: very shortwavelengths used in early airborne radarsystems but uncommon today.

� X-band: used extensively on airbornesystems for military reconnaissance andterrain mapping.

� C-band: common on many airborneresearch systems, ERS-1 and 2 andRADARSAT).

� S-band: used on board the RussianALMAZ satellite.

� L-band: used onboard American SEASATand Japanese JERS-1 satellites andNASA airborne system.

� P-band: longest radar wavelengths, usedon NASA experimental airborne researchsystem.

Wavelength ranges or bands of microwave

Ranges and bands were given

code letters during World War II,

and remain to this day.

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Wavelength ranges or bands of microwave

Band Designations

(common wavelengths Wavelength (λ) Frequency (υ)

shown in parentheses) in cm in GHz

_______________________________________________

Ka (0.86 cm) 0.75 - 1.18 40.0 to 26.5

K 1.18 - 1.67 26.5 to 18.0

Ku 1.67 - 2.4 18.0 to 12.5

X (3.0 and 3.2 cm) 2.4 - 3.8 12.5 - 8.0

C (7.5, 6.0 cm) 3.8 - 7.5 8.0 - 4.0

S (8.0, 9.6, 12.6 cm) 7.5 - 15.0 4.0 - 2.0

L (23.5, 24.0, 25.0 cm) 15.0 - 30.0 2.0 - 1.0

P (68.0 cm) 30.0 - 100 1.0 - 0.3

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Types of radar

� Nonimaging radar� Traffic police use handheld Doppler radar system determine the speed by

measuring frequency shift between transmitted and return microwave signal

� Plan position indicator (PPI) radars use a rotating antenna to detect targets over a circular area, such as NEXRDA

� Satellite-based radar altimeters (low spatial resolution but high vertical resolution)

� Imaging radar� Usually high spatial resolution,

� Consists of a transmitter, a receiver, one or more antennas, GPS, computers

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Radar Nomenclature14

� Azimuth Direction

� – direction of travel of aircraft or orbital track of satellite

� Range angle

� – direction of radar illumination, usually perpendicular to azimuth direction

� Depression angle

� – angle between horizontal plane and microwave pulse (near range depression angle > far range depression angle)

� Incident angle

� – angle between microwave pulse and a line perpendicular to the local surface slope

� Polarization

� – linearly polarized microwave energy emitted/received by the sensor (HH, VV, HV, VH)

Radar Nomenclature15

� Radar imagery has a different geometry

than that produced by most conventional

remote sensor systems Therefore, one

must be very careful when attempting to

make radargrammetric measurements.

� Uncorrected radar imagery is displayed in

what is called slant-range geometry, i.e., it

is based on the actual distance from the

radar to each of the respective features in

the scene.

� It is possible to convert the slant-range

display into the true ground-range display

on the x-axis so that features in the scene

are in their proper planimetric (x,y)

position relative to one another in the final

radar image.

Slant Range vs. Ground Range16

� Radar layover

� At near range, the top of a tallobject is closer to the antenna than isits base. As a result, the echo fromthe top of the object reaches theantenna before the echo from thebase.

� Because the radar can measure onlyslant-range distances, AB and BC areprojected onto the slant-range

domain, represented by the line bac.

Geometric errors17

� Radar foreshortening,

� It occurs in terrain of modest to highrelief depicted in the mid- to far-range portion of an image

� Here the slant-range representationdepicts ABC in their correctrelationships abc, but the distancesbetween them are not accuratelyshown. Whereas AB = BC in theground-range domain, ab < bc whenthey are projected into the slant range

Geometric errors18

� Polarization of the radiation is also important. Polarization refers to theorientation of the electric field.

� Most radars are designed to transmit microwave radiation either horizontallypolarized (H) or vertically polarized (V).

� Similarly, the antenna receives either the horizontally or vertically polarizedbackscattered energy, and some radars can receive both.

� Four combinations of both transmit and receive polarizations as follows:

� HH - for horizontal transmit and horizontal receive,

� VV - for vertical transmit and vertical receive,

� HV - for horizontal transmit and vertical receive, and

� VH - for vertical transmit and horizontal receive.

� The first two polarization combinations are referred to as like-polarized andthe last two combinations are referred to as cross-polarized

Polarization19

� The spatial resolution of radar system iscontrolled by several parameters

� For imaging radar, the size of groundresolution cell is controlled by the pulseduration, ground range and beamwidth

� Pulse duration and ground range dictatethe spatial resolution (range resolution) inthe direction of energy propagationreferred to as the range resolution

� Beam width determines the spatialresolution in the direction of flightreferred to as azimuthal resolution

Spatial Resolution20

Spatial Resolution

Effect of pulse length. (a) Longer pulse length means that the two objectsshown here are illuminated by a single burst of energy, creating a single echothat cannot reveal the presence of two separate objects.

(b) Shorter pulse length illuminates the two objects with separate pulses,creating separate echoes for each object. Pulse length determines resolutionin the cross-track dimension of the image.

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Spatial Resolution

Azimuth resolution. For real aperture radar, the ability of the system toacquire fine detail in the along-track axis derives from its ability to focusthe radar beam to illuminate a small area.

Beam width, in relation to range (R), determines detail—region 1 atrange R1 will be imaged in greater detail than region 2 at greater rangeR2

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� SLAR (Side-Looking Airborne Radar)- develop in the 1950's- airborne, fixed antenna width, sends one pulse at a time and measures what gets scattered back- resolution determined by wavelength and antenna size (narrow antenna width = higher resolution)

� SAR (Synthetic Aperture Radar)- also developed by those responsible for SLAR, but this configuration is not dependent on the physical antenna size although to achieve higher resolution the receiving antenna components and transmitter components need to be separated.- "synthesizes" a very broad antenna by sending multiple pulses

Types of Imaging Radar23

Synthetic Aperture Radar24

� Look direction, the direction at which the radar signal strikes the landscape, isimportant in both natural and man-made landscapes.

� Look angle, the depression angle of the radar, varies across an image, fromrelatively steep at the near-range side of the image to relatively shallow atthe far-range side

� In natural landscapes, look directions especially important when terrainfeatures display a preferential alignment.

� Look directions perpendicular to topographic alignment will tend to maximizeradar shadow, whereas look directions parallel to topographic orientation willtend to minimize radar shadow

Radar Shadow25

� The portion of the outgoing radarsignal that the target redirectsdirectly back towards the radarantenna is termed as backscattering

� When a radar system transmits apulse of energy to the ground (A), itscatters off the ground in alldirections (C). A portion of thescattered energy is directed backtoward the radar receiver (B), andthis portion is referred to as"backscatter".

Backscatter26

Speckle

A=Specular Reflection,

B=Diffuse scattering Corner Reflector Volume Scattering

SAR images are subject to fine-textured effects that can create a grainysalt-and-pepper appearance when viewed in detail called speckle

Speckle is created by radar illumination of separate scatterers that aretoo small to be individually resolved

Volume scattering is the scattering of radar energy within a volume or medium, and

usually consists of multiple bounces and reflections from different components within

the volume

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� The incidence angle is defined as the angle betweenthe axis of the incident radar signal and aperpendicular to the surface that the signal strikes

� If the surface is homogeneous with respect to itselectrical properties and “smooth” with respect tothe wavelength of the signal, then the reflectedsignal will be reflected at an angle equal to theincidence angle, with most of the energy directed ina single direction (i.e., specular reflection).

� For “rough” surfaces, reflection will not depend asmuch on incidence angle, and the signal will bescattered more or less equally in all directions (i.e.,diffuse, or isotropic, scattering)

Incident angle and scattering

Incidence

Angle

Local incidence angle

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� A radar signal that strikes a surface will be reflected in a manner thatdepends both on characteristics of the surface and properties of the radarwave, as determined by the radar system and the conditions under which it isoperated

Surface Roughness

� According to Rayleigh roughness criterion

� h = the vertical relief (average height of surface irregularities)

� = the radar wavelength (measured in cm)

� = the depression angle

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Surface Roughness30

Penetration of Radar signals31

� Flood mapping, Snow mapping, Oil Slicks

� Sea ice type, Crop classification,

� Forest biomass / timber estimation, tree height

� Soil moisture mapping, soil roughness mapping / monitoring

� Wave height monitoring

� Crop yield, crop stress

� Flood prediction

� Landslide prediction

Applications32

Comments….

Questions….

Suggestions….

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I am grateful to all the information sources (regardingremote sensing and GIS) on internet that I accessedand utilized for the preparation of present lecture.

Thank you !

Feel free contact

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