On occasion there is concern about additional hazards such as shallow water and / or shoals in the operating area for a particular survey. Meridian has also provided the equipment and personnel to undertake Bathymetry and Side Scan Sonar surveys as preliminary reconnaissance surveys when this information is critical to evaluating the operational constraints a survey may expect.
When planning a reconnaissance survey it is important to remember that this is a coarse survey to identify specific hazards to the movements of the seismic vessels and the seismic equipment deployed. In general, regardless of how precise a given sea floor mapping survey may be, the seismic vessel will not go within 500 metres of any hazard identified. There is therefore no benefit to performing a very expensive, high precision survey, at this stage of the exploration of the field. Modern improvements in design and manufacture have created a convenient set of hardware which is ideally suited to the reconnaissance surveys.
The Bathymetry survey to define the water depth over the work area can use a single frequency echo sounder with a light weight transducer head, because the survey is only interested in the shallow water. This category of echo sounder will now digitally record the water depth as the survey vessel passes over areas of interest. This unit will be interfaced with navigation software to record vessel position and raw water depth simultaneously. Post processing has also been simplified, and can quite often be completed on the survey vessel before leaving the site.
The bathymetry data can be supplied as an AutoCad plot which integrates directly into the navigation software on the seismic vessel, so the bridge has a clear image of water depth along whichever survey line it is following at any given time.
The Side Scan Sonar instrumentation has also become much better suited to reconnaissance surveys. Modern Sidescan Sonar Systems are noted for their performance and robust, user-friendly design. They are supported by a complete range of accessories, including the portable winch, to aid the surveyor’s task, digital presentation and data logging to allow prompt identification and locating of sea floor hazards seen on the display. For shallow water depths the portable winch is generally not required due to the light weight of the tow fish and ease of deployment.