Use of robotic systems such as remotely operated vehicles (ROVs) is ever evolving. There are numerous challenges when operating in an underwater environment - unstable conditions, poor visibility, hazardous structures, and unpredictable currents, to name a few. Beyond these environmental conditions, operating underwater can have task-specific requirements. A small, properly equipped maneuverable ROV can deal with most underwater environmental challenges and provide sufficient information for making decisions.
ROV systems are used to conduct surveys, search and locate targets, and collect data and/or physical samples as well as complete other tasks. Virtually all missions require some form of visual image collection. However, capturing optical data can often be difficult due to poor visibility. Water turbidity, poor lighting, and the inability to get within close proximity of the target are but a few of the obstacles.
ROV systems today are fitted with increasingly improved optical cameras, bright lighting systems, and video enhancement technologies. However, when visibility is compromised by turbid water conditions, optics are often of little use. Light wavelengths are small compared to the size of suspended particles. These particles cause the light waves to be blocked, deflected, and scattered, yielding poor or no visibility of the target. However, sound wavelengths are large compared to these suspended particles, which in turn allows most of the energy to pass. Knowing this, underwater operations have long become dependent on sonar technology to not only locate, but also help identify targets in turbid water.
Scanning sonars have provided ROV operators a tool to help locate and navigate to targets. Once located, the targets can frequently be identified by an optical visual inspection. Added benefits of a scanning sonar is its full 360 degree scan sector that provides valuable situational awareness. Use of lower frequencies allows for longer ranges, and a single channel transducer can provide clean, low noise images. Improving the technology to a multibeam imaging sonar provides fast image update rates, which allows real-time imaging from a moving platform and/or moving targets. Rather than an operator having to interpret low-resolution scanning sonar data, they may now be provided with more videolike imagery.
The performance of an imaging sonar is determined by a number of specifications, most notably the operating frequency, acoustic beam width, and dynamic range. Generally speaking, a lower frequency increases the distance at which an object can be detected, whereas higher frequencies and smaller beam widths deliver clearer images and higher definition at closer ranges.
Sound Metrics, the creators of the high-resolution DIDSON (Dual-frequency IDentification Sonar) lens based multi-beam sonar has developed their next generation sonar, ARIS (Adaptive Resolution Imaging Sonar). The ARIS uses the same DIDSON technology to beamform crisp, clear images at the speed of sound through acoustic lenses. ARIS models include the Explorer 1200 (1.2 and 0.7MHz frequencies), the Explorer 1800 (1.8 and 1.2MHz frequencies), and the all new Explorer 3000 (3.0 and 1.8MHz frequencies). Sound Metrics is introducing a whole new category of High Definition Sonar imaging with the Explorer 3000. Its improved image clarity is the result of increasing the physical transducer count by 30% and using a new lens prescription that produces finer resolution from each transducer. All the DIDSON Technology sonars offer a lower frequency used for object detection along with a higher frequency for identification imaging.
SeaBotix Inc. has developed a new class of MiniROV systems with the 2011 launch of the vectored Little Benthic Vehicle (vLBV). The vLBV was the culmination of years worth of field operations, client feedback, and development. Vectored platforms offer a number of advantages over conventional ROVs, including greater stability, increased maneuverability, enhanced capability, and improved sensor payload. By placing four thrusters in a vectored configuration, the ROV can maneuver around objects in more demanding conditions. All these features of the vLBV have been realized in a system weighing only 18kg, which does not require any special deployment/handling equipment.