survey intro 2

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MARINE SURVEY

Sivakholundu


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Why to Survey

ExplorationHydro carbon, minerals, living resources

Development workscoastal construction, port development, etc

Understand Dynamic EarthPhysical processes wind, tide, current

Changes in physical set up are continuous

MiscellaneousDefence, political


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What to Survey

Physical Set up

Depth / Elevation

different layers of earth surface

Material composition

Magnetic and gravitational variation

Tide

Current

Waves

Seawater properties


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Survey operationat sea

Measure Position

Measure any other

attribute (Depth, etc) atthat position


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to measure position you need to

know about..

Datums and reference surfaces

Coordinate systems and map projections

Position fixing general principles

Position fixing GPS


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measuring the attribute will

require knowledge about.

Types of Surveys

Survey Equipment

Acoustic Sensors

Conducting a survey


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Coordinate Systems

Are needed to

to define locations of interest

to know relations between locations

(Distance, direction)

to manipulate data and get derivatives -

Area, Volume, gradient, etc


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Surfaces

Survey area can be assumed to be simple

two dimensional plane - if distances

involved are small enough


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Surfaces .

Effect of curvature of earth becomes

significant if distances involved are longer

- and they have to be accounted for.Early surveyors and navigators

assumed that earth is a sphere.


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Surfaces .

Earth is not a sphere.

It is a oblated sphere - one having a slight

bulge at the equatorial region

Present surveyors and navigators

adopt a spheroid (Ellipsoid)

to represent the earth

surface


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Ellipse

For the earth:Major axis, a ~ 6378 km

Minor axis, b ~ 6357 km

Flattening ratio, f = (a-b)/a

~ 1/300

a

b


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Ellipsoid or Spheroid

Rotate an ellipse around an axis

O

X

Z

Ya ab

Rotational axis


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One more surface..

Earth surface

EllipsoidSea surface

Geoid

Mean Sea Level is a surface of constantgravitational potential called the Geoid


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WGS-84 Ellipsoidal Height


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Geodetic DatumsLocal/regional datum:

* Approximates size and shape of the earth on a local, regional scale

* geometrical centre of the spheroid not necessarily coincident with geocentre

* well suited to surveying over the areas they were defined for - inadequate for global satellite

surveying systems.

Best fitting Global

datum Eg. WGS-84

Best fitting

regional datum

Eg. Everest


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Geoid and Ellipsoid

Ocean

Geoid

Earth surface (Topography)

Ellipsoid

Gravity Anomaly

Mean Sea level = Geoid

&Elevation is measured from the Geoid


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numerical or geometrical quantity or set of quantities which serve asa

reference or base for other quantities

The adopted coordinates (after and adjustment of measurements

comprise the datum)

The spheroid is a simple geometrical reference surface to which the

coordinates are referred

horizontal or vertical, datums

regional or global different best-fitting reference spheroids have been

defined in different parts of the world because of the undulating

Geodetic Datums


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Issues related toDatums used in India

Everest WGS-84

All old maps are in Everest New survey is being carried out on WGS-

84

Best fitting model for the region Satellite positioning can work in Globaldatums only

Orthometric Heighting can be related to

local datum more readily

Spheroid and Geoid separation is larger

(~100m) making orthometric heightingmore cumbursome

Datum transformation parameters are not readily available at present for all regions

Wrong assumption of Datum can lead to an error as much as 300m in horizontal position

Datum and spheroid must be specified to define horizontal position - Latitude andlongitude alone will not be sufficient. Without this information a single coordinate setcan refer to different positions

Datum Transformation parameters have limited area of applicability (From Indian everestto WGS-84). Parameters for Chennai region is different than Mumbai region.


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Equator

Latitude and Longitude

Meridian of longitude

Parallel of latitude

X

Y

Z

N

EW

P

OR

=0-180E

=0-90N

Greenwich

meridian=0

=0

- Geographic longitude - Geographic latitude

O - Geocenter=0-180W


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Map Projection

the transformation of a curved earth to a flat

map

is any systematic arrangement of meridiansand parallels portraying the curved surface

of the spheroid upon a plane


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Geographic and Projected Coordinates

(, ) (x, y)Map Projection


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Types of Projections

Conic (Albers Equal Area, Lambert

Conformal Conic) - good for East-West

land areas Cylindrical (Transverse Mercator) - good

for North-South land areas

Azimuthal (Lambert Azimuthal Equal Area)- good for global views


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Mercator Projection

Suitable in low latitudes

Meridians are parallel through out

Distortion becomes larger with higher latitudes

Usage of Graticules makes it inconvenient for purposes other thannavi ation


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Click to edit Master text styles

Second levelThird level

Fourth levelFifth level

Transverse Mercator


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Based on transverse Mercator

projection with some fixedproperties

Covers Earth surface between 80South and 84 North

60 north-south zones 6 degrees oflongitude wide

Each zone overlaps degree intothe adjoining zones

False origin of 500,000 meters westof the central meridian of eachUTM zone

500,000 m

Central

Meridian

0o

Universal Transverse Mercator


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Survey operationat sea

Measure Position

Measure any other

attribute (Depth, etc) atthat position


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measuring the attribute will

require knowledge about.

Types of Surveys

Survey Equipment

Acoustic Sensors

Conducting a survey


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Types of Survey

Topographic Survey Land survey, features, soil type, road,drainage, Buldings, etc

Bathymetric Survey Map the depth variation

Geophysical Survey Map the sub-seabed details, Layer

thickness, material type, etc

Geotechnical Survey Map the sediment characteristics seabed

material particle size, strength etcMagnetic Survey Map the magnetic anomaly, search for

embedded ferrous objects

Gravity Survey - Map the gravity anomaly

More


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Acoustic SystemsSea water is a bad conductor for light / Electromagnetic waves

attenuates within few meters of passage

Acoustic signals are excellent tools for probing underwater. They can

pass through water mass and also Seabed for a limited depth.

Almost all major probes are acoustic in marine use

Echosounder

Side scan Sonar

Sub bottom profiler

Acoustic ranging systems

Current Profiler

E h d


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EchosounderAn echosounder sends out a sound pulse and waits for its

echo reflected from the seabed. The velocity of sound is a

known quantity and hence the time elapsed is a measure ofdepth.


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Types of Echosounders

Single Beam - Simple system to install and interface Frequency

ranges upto ~ 250 kHz produces a single profile

along the vessel track

MultiBeam - Relatively Complicated- requires motion of vesselto be fully monitored- Frequency ranges upto 450 kHz

The System available in NIOT can measure upto 240

beams simultaneously.

Parametric - Uses two high frequency signals to generate a new

low frequency (difference) signal to penetrate into

the seabed. Acts as a combined Echosounder and a Sub-

bottom profiler.


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Multibeam Echosounder


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Tide .

CD

Echosounding includes water column

caused by tidal variation

Hence tide is observed during sounding

operation and raw soundings are reduced

to Chart Datum

MSL


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Side Scan Sonar

DF-1000 Towfish

Records tonal variation of reflected signal from objects /seafloor

The tonal variation depends on material characteristics

It is possible to qualitatively judge the sea bed composition

sand/rock/clay or objects ship wreck, pipeline, structures

Normally towed behind

the survey vessel to avoid

vessel noise

Used in seabed

engineering investigations,

geological mapping and

search operations 50


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Side Scan Sonar

Track of Tow

Fish


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Side Scan Sonar


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Side Scan Sonar

Sample of Ship Wreck


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Sub-Bottom ProfilerSound waves travel into the seabed and get reflected at

different depths depending on their frequency andmaterial nature. This property is used in SBP to

investigate the sub-bottom layers and formation details


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Sub Bottom Profiler

SB-216S

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Boomer and Sparker are used for sub-bottom profiling.They use very low frequency and High Energy sound

waves to accomplish the sub-bottom penetration.

The later types known as chirp sonar produces a pulse

sweeping over a band of low frequency (eg. 0.5 to12kHz). The reflection of signal is a function of

frequency used. Different layers of seabed

respond to different frequency component

of outgoing signal. The reflection of each

component corresponds with a layer change.


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Sub Bottom Profiler Sample record


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Sample Sub-bottom profile


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Sample Sub-bottom profile


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Sample charts


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Thank you


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design water levels

1. Tide

- Highest Astronomical tide

- determination of HAT, MSL

3. Surge

- modeling requirement

5. Wave setup

7. Waves

- significant wave- extreme value statistics

-


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Design water levels


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Thank you

survey intro 2

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