DEEP SEA UNDERWATER SURVEYING

B.BINITHAM.TECH ENV ENGG

14220002

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INTRODUCTION

Underwater survey is the technique used for conducting impact analysis and shoreline inventory of submerged aquatic resources.

It is used to determine the depth, sea floor conditions , sub bottom profile, tracking , positioning etc in the marine water.

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It provides location data of previously

unobtainable accurately for specific sample sites, hazards, and marine resources.

Identifying, mapping and recording the exact locations of submerged aquatic resources and unwanted hazards in low visibility waters.

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METHODS

• Digital sonar• Scanning or side-scan sonar• Sub-bottom profile system• Differential global positioning system (DGPS)• Electronic tide guide• Digital CCTV

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Digital sonar

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• A narrow-beam sonar head generates a sound pulse from the sonar.

• The sound frequency and pulse can be modified to suit conditions.

• When the sound pulse hits a target, it bounces back and the echo appears as a data point. 6

• Data points are calculated using the angle of the sonar head, the speed of sound in water and the travel time.

• Using sonar, data can be gathered from a vertical dam face, across the bottom, under overhangs or other vertical structures, or inside pipes and sewers.

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Scanning or side-scan sonar

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• Side-scan sonar is used to investigate seafloor conditions such as scour patterns, obstructions, the type and size of debris, and the condition of pipelines and cables.

• Side-scan sonar is also used for dredging operations and environmental studies.

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• It uses a sonar device that emits fan-shaped pulses toward the seafloor across a wide angle perpendicular to the path of the sensor through the water.

• Side-scan data are frequently acquired along with sub-bottom profiler data.

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Sub-bottom profile system

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• Especially useful in surveys of river crossings.

• Sub-bottom profiling systems measures the positions of objects that exist below the bottom.

• A sound source emits a signal downwards into the water and a receiver records the reflected return. 

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• The system uses this reflected energy to provide information on features beneath the bottom.

• Sub-bottom profiling systems can be useful for calculating pipe cover or exposure, or areas of concern.

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Differential global positioning system (DGPS)

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• DGPS uses a network of fixed, ground-based reference stations to broadcast the difference between the positions indicated by the satellite systems and the known fixed positions.

• Depending on the accuracy required, it uses a Trimble Pro XRS (sub metre) or RTK GPS (centimetre) receiver.

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• The Pro XRS offers GPS, WAAS(Wide Area

Augmentation System) , EGNOS(European Geostationary Navigation Overlay

Service), satellite differential, and beacon capabilities.

• It also uses patented multipath rejection technology to remove multipath signals in reflective environments.

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Electronic tide guide

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• To track water elevation a submersible pressure transmitter is used.

• The tide gauge stores pressure, temperature and time data, and the data is also monitored in real time via a radio link.

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Digital CCTV

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• Digital CCTV cameras provide high resolution images that do not suffer degradation in transmission or when copied.

• The images can be digitally enhanced for greater clarity, and can be easily catalogued and reviewed.

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• Images acquired in this way can also be displayed in combination with sonar information.

• The images are recorded in digital format to DVD’s.

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Conclusion

Underwater surveying can be used for locating specific hazards and marine resources with previously unobtainable accuracy at a low cost.

And it could be helpful for determining various underwater parameters in an environmental friendly way.

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Reference

• http://www.aquacoustic.com/technology.php

• aaus-underwater-survey-technique-08• http://link.springer.com/chapter/10.1007%

2F978-3-540-48113-3_36• Wikipedia

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THANK YOU

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