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An Introduction to Modern Surveying Techniques

A. K. Sarma

Civil Engineering Department

Indian Institute of Technology Guwahati

History of Surveying

• What is surveying

• History of surveying techniques – In ancient Egypt (3000 BCE), when the Nile River

overflowed its banks and washed out farm boundaries, boundaries were re-established by surveyor, through the application of simple geometry.

• History of surveying in India– Some form of mapping was practiced in India during

the Indus Civilization (ca. 2500–1900 BCE).

– Construction of large-scale plans and other cartographic works has occurred continuously at least since the late Vedic age (first millennium BCE)

Modernization

• Development in other field of science

– Modernization in surveying equipments

– Modernization in surveying technique

• Many a time both goes hand in hand

– Example: Triangulation Trilateration

Survey Equipments and Systems• Rope, measuring tap

• Chain

• Compass

• Plane Table

• Level

• Theodolite

• Electronic theodolite

• EDM (Electronic Distance Measuring Equipment)

• Total Station, Automatic Total Station

• Sounding equipments (Hydrographic survey)

• Aerial Photogrammetric survey (1858, 1906)

• Satellite Remote Sensing(1972, 1988(India))

• GPS, DGPS

• GIS has improved utility of Remote Sensing and GPS

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Fundamentals of EDM

• For distance measuring EDM uses either

– Infrared (light wave) [ 0.5 to 20Km]

– Microwaves (radio wave) [up to 50Km]

• Microwave requires transmitter/receiver at

both end

• Infrared requires a reflector at one end

• EDM can be mounted on a standard

theodolite or Electronic theodolite

Fundamentals of Electronic Theodolite

• It contains circular encoders, which can sense the rotation of the spindles and the telescope

• These rotations are converted to horizontal and vertical angles and displayed digitally

• The angle recorded can be entered in filed book or can be stored in digital form and can be downloaded to a computer for future use

• Circle can be set to zero by simply pressing the button

• Laser theodolite has additional facility for more accurately bisecting the target.

Fundamentals of Total Station

• Basically TS (also called Electronic Techeometer) is a combination of EDM and Electronic Theodolite

• They are equipped with a microprocessor for reduction of observed data

• It can display– horizontal angle, vertical angle, slope distance

– Horizontal distance, elevation difference,

– Coordinates

• Automatic Total Station has – motorized EDM and Theodolite, and

– Automatic Target Reorganization

– This makes the survey a single man job

Art and Science of obtaining

information about an object

without being in direct physical

contact with the object

Fundamentals of Remote Sensing

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Elements of Remote Sensing

�Energy source

�Radiation

�Sensor

�Receiving and processing station

•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)

Advantages of Remote Sensing

�Large area coverage

�Repetitive coverage

�Easy data acquisition at different scale and resolution

�Multidisciplinary uses

�Cost effective for surveying the details large area

�Computable to computer analysis

�Data coverage of inaccessible areas

�Less time consuming

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Atmospheric Window

SensingSensing Atmospheric Atmospheric

windows windows

(wavelength)(wavelength)

VisibleVisible 0.380.38--0.72 0.72

micrometermicrometer

Near and Near and

Middle Middle

infraredinfrared

0.720.72--3 3

micrometermicrometer

Thermal Thermal

Infrared Infrared

sensingsensing

88--14 micrometer14 micrometer

RADAR RADAR

sensingsensing

1mm1mm--1m1m

Platforms of Remote Sensing

Air borne platforms-

Aerial remote

sensing

Space borne

platforms-Satellite

remote sensing

Remote Sensing Satellite

�The first Remote Sensing satellite was

launched by USA in 23rd July, 1972

�The First Indian Remote Sensing satellite

is IRS-1A was launched in 17th March

1988

Types of Sensor

• Active • Passive

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Passive Sensor Vs. Active Sensor

Passive� Sun is the source of illumination� Operates in the visible and infrared region of the

electromagnetic spectra

Active� Own energy source for illumination

� Can use wavelengths (1mm to 100m) that are not sufficiently provided by the sun

� All weather capability to acquire data

� Day and night capability to acquire data

� Have better control the way is illuminatedExample:

RADAR( Radio Detection and Ranging)

LIDAR (Light Detection and Ranging)

RESOLUTIONQuality of information derived from RS images stronglyinfluenced by spatial, spectral, radiometric and temporalresolution of the sensor

• Spatial Resolutioninstrument resolving power needed to spatially discriminatethe smallest object

• Spectral resolutionencompasses the width of bands used from the wavelengthsof the EM spectrum.

• Radiometric resolutionquantify No. of discernible signal levels in a band, {sensor’sability to discriminate radiance differences (NE∆ρ)}

• Temporal resolutiontime interval between imaging collections over the samegeographic location

Resolutions

• Spatial

resolution

• Spectral

resolution

• Radiometric

Resolution

• Temporal

Resolution

0July 23

0

10-bit range

0 63

8-bit range

255

10230

6-bit range

Time

July 1 July 12August 3

16 days

July 18 August 3July 2

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Interaction of EMR with atmosphere

• Transmission

• Scattering

• Reflection

• Absorption

SpectralReflectance

High

Spectral Region

Blue Green Red Near IR Mid IR

Water

Vegetation

Soil

Spectral Signature

Estimating Elevation Information

• How elevations are measured

– Single image analysis

– Analyzing image pair

• Stereo Image

• What kind of errors there can be

Scale Variation

2 cm

• Occurs in all photography

Scale varies across the photography

6 cm

House width = 8m

Scale is 1:400

Scale is 1:133

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Scale Variation

• Same effect seen in vertical photography

House width constant (8m), width in photographs varies,

therefore scale varies

Sensor Attitude/Orientation

Oblique

More Oblique

Vertical

2

3

11

Internal Sensor Errors

Lens distortion and errors cause the light rays to deviate

IMAGE or EXPOSURE PLANE

Stereo Pair• A block should have at least one pair of images which

overlap:

Stereo Pair

Overlap Region

60% Overlap

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Global Positioning System: Principle and Applications

Location of an un-know point in a 2D plane with reference to

object in the same plane

Working Principle of GPS

Location of an un-known point in 3D Space

Distance =

Speed of light x

time

Distance = Speed of

sound x travel time

Distance =

Speed of the signal

X

Time to receive the

signal

Determining Location with the help of satellite

Unknowns are:

Horizontal position: X

and Y coordinates

Vertical Position: Z

coordinate

Receiver Clock Error

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Importance of

Time Synchronization of Clocksfor

Accuracy in Distance [Time required for a signal to reach receiver from a

overhead satellite position is just 0.06s]

Location of a point with reference to satellite

• Need minimum of four satellites whose positions are known at the time of measurement

• US Defense Department launched 24 satellites (NAVSTAR GPS (Navigation Satellite and Ranging GPS (1978-94)) in such a way that at least 6 satellites remain in view from any point of earth surface at any instant of time

• Distance from the satellites to the receiver need to be calculated accurately

Need of 4 Satellites• Measured pseudo-ranges are contaminated by the

satellite and receiver clock synchronization errors

• Correcting the satellite clock errors may be done by applying the satellite clock correction in the navigation message

• The receiver clock error is treated as an additional unknown parameter in the estimation process

• Thus unknowns are: three for the receiver coordinates and one for the receiver clock error.

• As the satellite coordinates are given in the WGS 84 system, the obtained receiver coordinates will also be in the WGS 84 system

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Datum, Mean Sea Level, Geoid…• The World Geodetic System (WGS) is a standard for use

in Cartography, Geodesy, and Navigation.

• It comprises a standard Coordinate Frame for the Earth, a standard Spheroidal reference surface (the datum or reference ellipsoid) for raw altitude data.

• The latest revision is WGS 84 (dating from 1984 and last revised in 2004), which will be valid up to about 2010.

• Earlier schemes included WGS 72, WGS 66, and WGS 60.

• WGS 84 is the reference coordinate system used by the Global Positioning System.

Distance Measuring• Receiver identifies each satellite's signal by its

transmitted distinct Coarse/Acquisition (C/A) code pattern (for general application, 1,023 Bit long ) or Precise (P) code pattern (for military application, 6.1871 × 1012 bits long )

• To measure the received time for each satellite, the receiver produces an identical code sequence using the same referenced to its local clock, starting at the same time the satellite sent it

• It then computes the offset to the local clock that generates the maximum correlation. This offset is the time delay from the satellite to the receiver, as told by the receiver's clock.

Errors in GPS and Scope of Elimination

• Errors include: – Ephemeris errors (giving the satellite's own

precise orbit) [Orbit shifting due to gravitational forces]

– Residual satellite clock errors – Multipath error (reflection of signals from Hill,

Building etc.)

– Atmospheric error (Ionospheric, Troposphericdelays

– Satellite geometry

– Satellite attitude– Site displacement effect

– Selective Availability

General ranges of error

Ionospheric effects ± 5.0m

Shifts in the satellite orbits ± 2.5m Clock

errors of the satellites' clocks ± 2.0m

Multipath effect ± 1m

Tropospheric effects ± 0.5 m

Calculation- rounding errors ± 1 meter

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Differential GPS (DGPS)• DGPS uses One stationary GPS at known location

and others moving to unknown locations (May be within 100Km or so)

• Base station and Roving GPS receiver

• It may be of Post Processing type or Real time type

• Stationary GPS calculates the error and implement correction in the moving GPS accordingly

• Accuracy gets improved to within two meters for moving objects and even better for stationary situations

Some Application of Remote Sensing, GIS and GPS

GPS Survey at Dhubri

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GENESIS OF SUALKUCHI EROSION

• located between two hillocks on the north bank

• As per curvature of the major channel, erosion should not have occurred in this portion of the channel reach

• But devastating Erosion has occurred

It is located between

Longitudes: 91º32‘E and 91º36‘E Latitudes:26º9‘N and 26º11‘N

Status in 2003

Eroded area

D/s

U/s

Soil deposited

Elevated river island

Imagery based study• Toposheet (1973)

and LISS-3 Imagery (2000, 2003) has revealed that the major causes are:

– natural hillock, present in the upstream

– deposition of sediment in the southern bank

Status in 2000

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Field Investigation

• Field investigation was carried out to measure the River Cross section and Flow Velocity

•GPS was used to record the location while flow meter, echo sounder and heavy weight were used for sounding.

Grid

Bathymetries

• Data collected from thesurvey carried out on 20-10-04 has been used along withthe other information forpreparing the bathymetry.

• For each cell the depthinformations are given asinput in the bathymetry fileon the basis of:– Observed depth

– General gradient (1: 10,000)

– Information from imageries

– Logical interpolation

Simulation Results

• Original condition

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Present conditionPUBLIC MEMORY

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GPS Points on Georeferenced Image Hilly and Plain Areas of the Watershed

Arial GPS Survey of Dibang

Dibang

Bramaputra

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Dam break

Inundation

map

Maximum

Probable Inundation

(time=2300sec

s)

Bor gul i

Ser am

Bi j ar i

B ango

Anpum

Namsi ng

A mar apur

M er

B or l ung

P ar buk

Ji yaNogpok

Ol d A bal i

K undi l

M ani pur i Bast i

Rani

Si ka T odeng

Si l l i

Kemi

Oyr amghat

3 2 km d / s

2 8 0 5' 3 9 ' 'N

4 8 km d / s

16 km d / s

28 14 ' 18 ' ' N

2 7 56 ' 57' ' N

11 km d / s

6 3 km d / s

Ni z amghat ar ea

Bomj i r

D eopani P r ot ect ed For est

D ense M i xed For est

D ense mi xed f or est

P asi ghat T own

P ugl am

Sant i pur

Nepal i Gaon

B ur abur i D eor i Gaon

Bor pukhur i

Chapakhowa

I s l ampur

Kukur mor a

Bosagaon

Ker i m P r ot ect ed For est

Reser ved For est

N

Bang o