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Shvoong Home>Science>Engineering>Sounding Method in Hydrographic Survey Summary

Sounding Method in Hydrographic Survey

Academic Paper Summary   by:LennySugar    
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In hydrographic surveying activity, depth of water is determined from observation of travel time of acoustic waves. Transducer transmit an acoustic pulse which is travels through the column of a water and then its reflected by the sea floor as a target back to hydrophone. Depth is calculated from the measured travel time ∆T multiplied by speed of sound in water (c) and then divided two.

  • Transmitter : have a function to generates pulses
  • Transducer : which converts the electrical power into acoustic power, sending acoustic signal into the water, receives the echo, then converts it into an electrical signal. It’s mounted on the ship’s hull.
  • Transmitter/Receiver (T/R) switch : to passes the power to the transducer.
  • Receiver  : amplifies the echo signal and sends it to the recording system.
  • Recorder : have a function to controls the signals emission, measures the travel time of the acoustic signal, stores the data, and converts time intervals into ranges.                         

When talking about the resolution of an echo sounder, it means either its detection capabilities or its measuring precisions. The resolution it self is a function of the following factors   like : Pulse duration, Angle of incidence of the acoustic wave front on the target, Nature of target, and beamwidth of Transmissions.

There are two major type of echo sounder, the Single Beam Echosounder (SBES) and Multibeam Echosounder (MBES).

Single Beam Echosounder (SBES) – this term actually is used for conventional single beam echo sounder which usually of the order of 30 degree of coverage angle. Along with the advancement in technology, narrow beam echo sounder have been available since the mid 1980’s. Narrow beam echo sounder are used to : Obtain depths directly under the vessel. The depth then used for safety of navigation or for sea floor mapping. It have advantages of avoiding wide beam biases which is often caused by under water slopes. And to Improve the quality of the data in terms of both resolution and accuracy.

Operation of the narrow beam echo sounder requires the transducer stabilized (mechanically or electronically) for roll and pitch motion of the vessel. To produce a narrow beam need larger size of transducer than for a wide beam. It have the impact on the equipment that becomes bulky and expensive.

Multibeam Echosounder (MBES) – this system are used to increase bottom coverage which will increase the productivity. Each of its narrow beam produced yields a resolution of the bottom sea is equivalent with that of a narrow single beam. The measurement accuracy itself is not better than the single beam, echo sounder. In fact, accuracy decreases as the swath angle increases.

MBES are divided into two groups, namely swath systems and sweep systems. A swath system produces multiple acoustic beams from a single transducer system (although dual transducer systems are used and, sometimes, the transmitter and receiver are separate). A sweep system simply consists of an array of single beam echosounders mounted on booms deployed on each side and perpendicular to the surface vessel. Most of this section will deal with swath systems, with an introduction to sweep systems at the end. The operation principle of the latter is much more straightforward than that of the former.

For further information you can download Sounding method lecturer in Relevant Links below this articles.   
Published: September 03, 2010   
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