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www.sea-technology.com June 2016 / st 25 I n 2014, the team at Marine Electron- ics Ltd. (MEL) realized that the rapidly expanding AUV and ROV sectors repre- sented a substantial market for a better 2D sonar. Although a version already existed in the company product range, a new digital model was needed, as the growth of the ROV and AUV indus- try offers a ready market for a 2D sonar that has lower power requirements and a more realistic price tag than a com- parable 3D sonar. To succeed, the new 2D sonar would also need to be small, lightweight and provide the customer with high-quality imagery at close to rel- atively distant ranges. MEL had already gained success with its range of digital 3D forward-looking sonars with models that included the Sea Echo, the Sea View 3264 and the Model 3248. It now ap- peared to be the right time to add a 2D digital sonar to the company's product range. The ultimate aim will be to have a range of 2D digital imaging sonars that will include the Dolphin Sea View, a bathymetry sonar and a new obsta- cle avoidance sonar (the 6201 V2). They will all run on the same system architecture but will vary according to opera- tional requirements for range and depth. Beginnings When the frst engineering meeting was held at Marine Electronics in Vale, on the U.K. Channel Island of Guernsey, the 2D sonar ceased to be a fgment of our imaginations and began to take on a life of its own. The meeting was at- tended by the three directors of the company—Brian Evans, Alan Green and Gordon Collier—and those who would ap- ply their expertise to different aspects of the new product's development. Collier would be in charge of overall design, while Richard Williams would be responsible for the FPGA (feld programmable gate array) design, Dan Bishop would be responsible for software and Simon Nicolle would over- see the mechanical aspects of design and construction. The team's frst task was to defne the basic parameters of the product. It would be a frequency-dependent, time-delay beam former with dynamic focusing for exceptional imag- ery in both short and long range. The demands of AUV and ROV builders and operators are such that the new sonar's power consumption had to be less than 15 W, yet the sonar had to be able to provide clear and legible images at any distance from 1 to 100 m. These basic performance benchmarks were then supple- mented with a "wish list" of features to further enhance the product. It was to be designed so that the same basic unit could be modifed and built to operate at any frequency requested by the customer. It was agreed at the outset that the new sonar's frequency would be 720 kHz, generally ac- cepted as the most versatile and best suited to the majority of applications, able to provide the clearest imagery at most ranges. But we wanted our 2D sonar to be adaptable for targets at distances specifed by customers. Much of the design was governed by the physics of acoustic imagery. To achieve the range and frequency that we wanted, the transmitter and receiver could be no smaller than 130 by 70 mm. We also wanted our sonar to share the same mounting format as that of our competitors to make it Development of Dolphin 2D Sonar High-Resolution Imagery for Growing ROV, AUV Market By Brian Evans • Paul Eastaugh The bathing pool serving as the frst Dolphin 2D sonar test site outdoors, with Castle Cornet in background.