Hydrographic survey can be defined as the art of collection of the various measurements of the waterbodies, the bottom topography of the waterbodies, to facilitate safe navigation of the water vessels. The domain of hydrographic survey may be of different scale ranging from a lake to river and oceans.
Domain of Hydrographic Survey :
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- Preparation of Nautical Charts : this is a graphical chart or representation of a coastal region. This chart represents the depth of the water at various places, the bottom reliefs of the concerned area, coastline details , navigational hazards, various anthropogenic features in & around the concerned area etc.
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- Maintenance of Harbor & Ports: Hydrographic Survey also plays a pivotal role in shipping and naval activities. It determines the depth of the water in the dock so that the vessel can anchors itself safely. With time sedimentation in the port or harbor front occurs which are dredged. This dredging is a part of the Hydrographic Survey because it involves a lot of hydrological studies.
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- Coastal Engineering : This involves the study of beach erosion & the various suggestive measure to overcome it.
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- Coastal Zone Management: This includes the study of the marine environment of the concerned area, preserve the natural marine environment if it is getting polluted by anthropogenic or natural means. The management also involves the mitigation of the coastal hazards.
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- Offshore Resource Development
There is one common data type which is generated in hydrographic survey is water depth. Moreover, it also involves the examination of the sea floor material like mud, sand and rock. This carries a profound influence on the aspects like anchoring, structure construction, dredging, cable routing and fisheries habitat.
Methods of Hydrographic Survey:
The methods of hydrographic survey has undergone a profound change with time.
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- Conventional Methods of Hydrographic Survey:
In early days Hydrographic Surveys involves the depth measurement by sounding pole and hand lead line where the positions are calculated by three-point sextant fixed on a reference point on map. The reading of this survey methods are analogue in nature, and it is an labor-intensive and time-consuming process. Thus, this method was not that popular.
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- Modern Methods of Hydrographic Survey:
Now a days all the renowned Hydrographic Communities, which performs the Hydrographic Surveys uses the latest technologies like Side Scan & Multi Beam Sonar . The SONAR technology is in much use now. SONAR stands for Sound Navigation and Ranging . SONAR uses sound waves to determine the depth of the water at various places. Now a days Multi-Beam SONAR technology is being used to determine the depth of the oceans and various water bodies. Multi-Beam SONAR involves the generation of the sound waves directly from the bottom of the ship which covers its surrounding ocean in a fan-like fashion and determines the bottom relief of the sea.
Processing of Hydrographic Data: an important aspect of Hydrographic Survey
The Hydrographic Survey data are processed by means of latest computer technologies. CAD software like Autocad are mainly used to generate the Digital Nautical Charts. The digital forms are in mylar “smooth sheets”. The scale of the digital charts varies from 1:10,000 and 1:20,000. The scale are mainly determined by the extent of the hydrographic data needed according to the various purposes.
National Ocean Service (NOS) and Office of Coast Survey (OCS) are the premier organization which carry out the Hydrographic Surveys.
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