A specific example of this problem is the need for concurrent use of an imaging sonar system and an acoustic positioning system. The weakness is that unless the sensor manufacturers collude to form a set of transmission standards, each sensor connected to the system ‘hogs’ the data transmission line to the detriment of other sensors needed for the task. The strength of this method is that the sensor vendor does not need engineering support from the ROV manufacturer in order to design these sensor interfaces. Most small ROV manufacturers simply provide a spare twisted pair of conductors for hard-wire communication of sensors from the vehicle to the surface. In The Maritime Engineering Reference Book, 2008 10.4.4.5 Data Transmission and Protocol These data are used to map boulders, sandwaves, reefs, seafloor instability features, pipelines, wellheads and ship wrecks. Features less than 1 ft in height can be detected. Reflected signals normally appear as dark areas on the record, whereas shadows behind the objects appear as light areas. Typical seafloor records are shown on fig. These factors must be taken into consideration when planning and costing an operation. Likewise, the turning time with long cables increases such that a deep-tow can take several hours to complete a line turn. Owing to the long length of the tow cable, surveyors have to allow for a “run-in” and “run-out” equivalent to the length of the tow to ensure that the required area is covered. A deep-tow system operating at 2000 m will reduce tow speed to 1 or 2 knots, greatly adding to the time (and cost) required for a survey. The normal tow speed for a side-scan survey is about 4 knots however, as operating depth increases, so the drag and strain on cables increase. They require a large powered winch and special launch and recovery systems and, therefore, are restricted to specialist survey vessels. The so-called “deep-tow” systems are very large towfish, 4 or 5 m long, and are heavy. The smaller, shallow water systems can be deployed from most vessels but the deeper towed systems operating at, say 1000 m depth, require a cable some 5000 m long and, therefore, a large winch. Side-scan sonars in towed fish require a powered winch and a suitable system for running out the cable normally an A-frame. Its use in the seabed classification systems is discussed below. Developments in sonar imaging continue to move forward rapidly. The clarity of the image, especially from the latest systems, is extraordinary. Side-scan sonar is probably one of the most useful tools developed for imaging the seabed. Developments to overcome this problem include using a second vessel (chase boat) to track the fish directly from above (costly), or deploying the side-scans on remote platforms, as discussed later. In deeper water, tracking a towed side-scan fish is problematic since the acoustic tracking systems are typically limited to a range of approximately three to four kilometers in 1500 m of water, at least 5 km of cable is required to position the fish at the required depth. Alternatively, the systems can be mounted in steerable ROTVs (remotely operated towed vehicles), ROVs (remotely operated vehicles) and AUVs (autonomous underwater vehicles). Side-scan sonar tow-fish can be towed deep or shallow depending on requirements. 60 kHz) provide long ranges (500 m), but with lower resolution. 500 kHz) provide high-resolution images, but with short (100 m) ranges. Example of side-scan sonar image of seabed
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