One of the most common uses for commercial underwater remote-operated vehicles (ROVs) is in conducting inspections of water tanks, ship hulls, and submerged infrastructure such as bridge components or dams. A critical element of these inspections is measuring the thickness of metal components like hulls or girders. How do ROVs conduct this type of measurement?
On the Aquabotix Endura line of high-performance commercial ROVs, we offer the Cygnus NDT Metal Thickness gauge as an optional accessory. These gauges use ultrasound technology to measure the thickness of metal objects underwater. By emitting an ultrasonic beam into the surface of the metal and analyzing the return sound, the Cygnus NDT can measure metal of thicknesses up to 10”, even through coatings such as paint up to 0.787” thick.
The Cygnus NDT is extremely easy to use. The included CygLink software allows the ROV operator to visualize the tool’s measurements remotely on the video feed. To make things even easier, the optional Cygnus Probe Handler automatically aligns the probe to the wall or item being measured, with 15 degrees of movement, even if the operator has not perfectly approached the measurement subject.
Tools like the Cygnus greatly enhance the utility of our Endura ROVs. As ROVs take on more responsible roles in things like underwater inspections, the need for tools such as the Cygnus will continue to grow.
Aquaculture and fisheries are a major source of the world’s protein production, and while fisheries are stagnating somewhat due to overconsumption, aquaculture production is growing at tremendous rates. As aquaculture facilities fill in the most desirable coastal locations, it is a certainty that future growth will take place in deeper water, where use of human labor will be more expensive and much more dangerous. One major job that will require significant automation in order to be economically practical is monitoring the aquaculture facility.
Aquaculture facilities require careful monitoring of a number of important parameters. The environment itself needs to be monitored for water quality, temperature, current, and so forth. Operators also need to be able to inspect hardware such as nets and cages, to count fish in particular enclosures, to locate dead fish, to check nutrient levels, to measure fish stress levels, and more. All of this information gathering is often done by human labor at onshore or shallow-water facilities, but that is impractical when the aquaculture facility is far offshore. Operators can’t hire from the local community when the local community is underwater – they have to use automated remote monitoring technology. Even in facilities where human labor is available, the cost and liability requirements of human workers will make automated remote monitoring a useful adjunct.
A number of different types of remote sensor can be used to monitor aquaculture operations, but one of the most generally useful instruments is also one of the simplest: a video camera. High-definition video cameras can capture a wide range of data both above the water and beneath the surface. Advances in robot vision, that is, the ability of computers to understand and utilize video feeds, mean that a huge number of video camera feeds can be interpreted by computerized systems. The aquaculture base can monitor types and numbers of fish in an area, examine nets and gates for damage, scan the bottom underneath fixed pens to check contamination levels, and even assess the weather pattern. AquaLens Connect, the underwater camera system from Aquabotix, has been built to withstand and excel in these challenging conditions. It features a full 1080p HD video with live view, push button recording, pan and tilt.
Aquaculture requires a great deal of management and assessment to be effective and profitable. Feed levels have to be continually adjusted to prevent excessive buildup of nutrients in the wastewater, fish populations have to be counted and their health checked, incursions from predators have to be seen to be mitigated, and physical infrastructure, always susceptible to storm damage, has to be kept in trim through regular inspection and maintenance. All of these tasks require that the aquaculture operator be aware of the condition of the facility. Stationary video cameras, as well as ROV-based roving cameras, provide a cost-effective means of achieving this goal.
Depending on which maritime body you ask, there are somewhere between 50,000 and 100,000 large ships sailing the world’s oceans, with cargo vessels, passenger ships, and warships making up the bulk of this number. Commercial vessels are required to have their hulls inspected on an annual basis, and military vessels generally follow a similar inspection regimen. There are various global and national bodies which provide certification standards, such as ABS (American Bureau of Shipping) and Lloyds of London. The goal of inspecting large vessels is to protect the owners of the ships, the crews, the passengers, the companies using the ships, and the insurance industry.
There are a variety of different certification standards, but the standard ABS inspection regimen is fairly typical for the industry. The ABS regimen is known as HIMP, which stands for Hull Inspection and Maintenance Program. HIMP has a three-tiered system of inspections, with annual inspections, three-year inspections, and five-year inspections. The three- and five-year inspection tiers encompass all the inspection areas of the lower tiers, while adding further areas of the ship to the inspection list. HIMP inspections cover the entire vessel, but the underwater portion of the survey is the trickiest for ship owners. Underwater surveys can be conducted by human divers, but increasingly this job is being handled by remote-operated vehicles (ROVs).
On a commercial vessel, the diver or ROV must provide visual data on the stern and rudder bearings, the sea suctions and sea valves, the propellers, and – most time-consuming - the hull plating. The inspection must look at any markings on the hull, all inlets and discharges, the rudder, the propeller, and all other objects that protrude from the hull. Corroded or damaged areas must be examined closely, and although thickness testing is not automatically part of the HIMP, any area found to be damaged or corroded is likely to be examined internally and have the thickness tested at the affected spot(s).
Military vessels follow a similar inspection regimen, and many military vessels will also have stencil-marked areas of the hull which need to be looked at. Inspections will check the hull and other secondary areas of the vessel for biofouling, to assess the need for having the ship’s bottom scraped. Inspections generally involve several waterline-to-waterline underwater traversals of the vessel, following the seams of welded sections. Propellers need to be inspected on both their front and rear facings.
In the early years of ROVs, their use in underwater hull inspections was relatively rare because the low video quality of early vehicles made their results of marginal utility to inspectors. Today however, with true HD displays and cameras on even consumer-level ROVs, these useful vehicles are an integral tool for large hull inspections. Since inspection divers need to be ABS-certified, many surveying companies are finding that it is highly useful to conduct a pre-inspection using an ROV only. This pre-inspection can find any problems that already exist so that they can be mitigated before the actual inspection, preventing a time-consuming, and expensive, temporary suspension of the vehicle’s certification when the inspector finds significant problems.
An offshore windfarm is an array of power-generating wind turbines usually built in the shallow water close to the coastline. Offshore wind power has three main advantages over land-based wind power: the wind directly offshore is usually stronger and steadier than it would be inland, the windfarm can be placed very close to the urban area that will be using the power, and there is less “not-in-my-backyard” opposition from local residents, since the local residents are mainly fish. The primary disadvantage of offshore wind farms is that they are much more expensive to build and maintain than other forms of low-carbon power generation.
The European Union is by far the world leader in offshore wind generation, with about 10 gigawatts (GW) of capacity. China and Canada both have modest windfarm operations and India is working on windfarm development, while the United States will open its first operational windfarm in late 2016 off Block Island in Rhode Island. Despite the high costs of offshore wind power development, projections of installed capacity continue to grow; the European Union expects to have between 20 and 40 GW of capacity online by 2020, and China perhaps optimistically expects to have 30 GW by the same year.
The primary component of an offshore windfarm is the wind turbine - the huge set of blades set atop an enormous pole, which spin as the wind blows. To achieve maximum effect, turbines need to be high off the surface of the water, so the pole must be very long - more than 200 meters.
Such a large structure must be anchored extremely securely to the seabed, and there are a number of ways in which this is done. Regardless of the exact nature of the structural engineering, the underwater structures of offshore wind turbines need to be inspected on a regular basis.
In the United States, offshore windfarm inspections will be under the oversight of the Department of the Interior’s Bureau of Safety and Environmental Enforcement (BSEE). BSEE’s draft standards draw heavily on the experience of the United Kingdom, and lay out an inspection regime that concentrates a great deal of attention on the turbines themselves, naturally enough. However, the underwater bases of the turbines come in for their share of attention as well.
BSEE draft standards will likely require that windfarms be inspected on an annual basis, with 20% of a farm’s individual turbines and foundations inspected in each annual cycle. Critical components should be evaluated annually, while less critical areas can be inspected as infrequently as every five years. Foundations need to be checked for structural health, bioaccumulation, scouring, spalling, and corrosion. Subsea cables need to be inspected for damage due to sand, marine animals, or anchoring.
BSEE suggests that general visual inspections can be carried out by ROVs, while close visual inspections need to be done by human divers.
BSEE standards are likely to recommend the use of ROVs specifically in order to reduce risks to human divers. Because there are often powerful tidal currents around the foundations of structures like wind turbine foundations, this can be a dangerous dive environment for humans. There is a great deal of general visual inspection work that needs to be done, but where an extremely close view is simply not required; the inspection needs to check the general condition of the pilings and caissons, for example. In this work, putting a human diver into the water isn’t necessary, as an ROV can provide the needed visual check.
(Primary source: http://www.bsee.gov/uploadedFiles/BSEE/Technology_and_Research/Technology_Assessment_Programs/Reports/700-799/747AA.pdf)
There are almost 80,000 dams in the US Army Corps of Engineers National Inventory of Dams (NID), and that isn’t even a comprehensive list; the NID only covers dams which reach a minimum height and which hold back a minimum volume of water. There are many thousands of other dams, on private and government land, which are used for irrigation, flood control, aquaculture, drinking water, industrial use, and a myriad of other applications. Although most of these dams are extremely useful, they can also pose a serious danger to people and objects downstream of the dam. For obvious reasons, dam failure can have catastrophic consequences.
Accordingly, it is critically important that dams be inspected on a regular basis.
The federal government, via the Federal Emergency Management Agency (FEMA), provides guidelines for inspections on dams under federal control. These guidelines suggest that dams should receive an informal “eyes-on” inspection as needed or following any significant incident at a dam (such as a flood, an earthquake, or vandalism), as well as a more thorough intermediate inspection of the dam and all related structures on an annual basis. Federal guidelines also suggest a formal full inspection of the dam be carried out at least every five years, with a full special inspection to be conducted when there is a major event such as a large flood or a major earthquake. Around 3,200 dams in the United States are owned outright by the federal government, and another 5,200 or so are not owned by the government but are located on government land. Although there are some complications about the regulation of those non-federally-owned dams, all told about 10% of the largest American dams fall under the federal guidelines.
The remainder of the dams in the United States are regulated by the state governments, with the notable exception of Alabama which leaves dams essentially unregulated. The state laws and regulations are a fairly diverse patchwork; some states require inspections to be paid for by the dam owners, while other states put that expense on the taxpayer. A few states like Texas do not have a formal inspection schedule at all (although inspections are strongly suggested) while most states have stringent schedules and extensive systems of classifications for which kinds of dams must be inspected and how often.
In general, however, in most places, dams are supposed to be inspected at intervals ranging from annually to every five years. The size of the dam’s impoundment (the volume of water the dam is holding back) and the population of the area in the dam’s potential flood area are the major factors determining how often and how stringent such inspections must be. Again depending on the location, inspections can be carried out by divers or by surface inspection, usually with at least some underwater work being required. Clearly, there is an astonishingly large amount of inspection work called for in the dam safety regulations.
ROVs play a major role in accomplishing the difficult task of inspecting dams while leaving them in service. Many dams are simply not able to be “turned off” so that an inspection can take place. Even when dams are equipped with the ability to dewater areas for inspection or repair, such dewatering is time-consuming and expensive. ROVs and human divers are able to work in areas of the dam without having to go through the dewatering process, saving large amounts of money.
One area where ROVs have saved enormous sums for dam owners is in assessing the need for cleaning of trashracks, reservoirs, and head ponds.
Rather than adhering to a calendar schedule for the dredging of such ancillary dam components, an ROV inspection using sonar can inexpensively check whether an area needs to be dredged at all.
Of even more importance than saving money is saving lives. At many dams, particularly hydropower dams, there are areas where it is very dangerous for a human diver to enter the water. High water flows and high pressure differentials can be life-threatening conditions. The use of an ROV allows dive teams to conduct preliminary safety assessments, measuring flow, depth, and water temperature before ever putting a human being into the water. ROVs have also been used to check safety concerns such as the open or closed status of a head gate, where a gap of a few inches in a nominally “closed” gate could pose a lethal risk to a diver in the area.
At large dams with deep water areas, ROVs have the ability to work deeper than human divers without needing mixed-gas equipment. (Divers going below 30 meters require decompression tanks and other specialized equipment that make a dive more expensive.) By using divers for shallow work at a dam, and ROVs for the deeper dives, a cleaning or inspection process can be accomplished at much less expense. In addition, ROVs can conduct survey work using tools such as multibeam sonar more efficiently than human dive teams. As dam infrastructure ages, inspections of components like downstream draft tube slabs require a great deal of precise surveying work to assess the condition of the slab.
As in many other areas of underwater work, ROVs are capable of making a large contribution to the jobs being done by human divers.
ROVs make underwater work safer, more effective, and less expensive.
There is a story – probably apocryphal – that one of the early Roman emperors was approached by an inventor who had created a steam-powered device for moving huge marble columns around, an invention of obvious interest to the monument-building Romans. The emperor rewarded the man for his innovation, but declined to purchase the device for the empire, stating that he had a city full of workmen who needed to eat, and the invention would put them all out of work. In the modern era, most of us recognize that the addition of powered machinery doesn’t permanently take jobs away from workers; rather, it changes the nature of their work, usually for the better. Today’s construction machine operators make a lot more money and work a lot more safely than did the burly gangs of workmen in Roman times.
In many ways, we’re smarter than our Roman forerunners. Today we are a lot more likely to see opportunity in new technology, not threats. Commercial divers sometimes worry about ROVs undercutting them on price for some kinds of jobs, but the opportunities for new business provided by ROVs are a much larger vein of possible work. ROVs represent an affordable way for divers to expand their businesses by increasing the human diver’s capabilities while simultaneously cutting costs and improving safety.
ROVs are not going to replace human divers – instead, they are going to add to those divers’ ability to work productively underwater.
Diving is difficult and often dangerous work. It’s uncommon for a client to need a diver to conduct a brief excursion in crystal-clear waters in order to do some trivial task. Rather, divers are asked to handle hard jobs in unpleasant and sometimes unsafe conditions. Many times, a job can’t be done because there’s no way to do it safely. ROVs can change that, because an ROV worth a few thousand dollars can be risked in many situations where a human life would be at too much risk. That ability to run additional risks with only hardware on the line can actually improve the ability of a dive team to take on a job, because the ROV can scout the work and establish whether or not it actually is a human-achievable job.
Many diving jobs involve a great deal of reconnaissance and scouting in order to do an hour’s worth of actual work. For example, in a salvage operation, a diver may spend days looking around a site and finding the items that are worth retrieving, then do the actual salvage work in an afternoon. However, all of that scouting time is just as expensive, just as dangerous, and just as exhausting as the actual paying work at the end. An ROV doesn’t require a trained commercial diver for its operation; the diver can hire support personnel (who work a lot cheaper) to do the scout work with a controlled ROV, then go into the water herself later on when the job is narrowed down. Same payday, but a lot less cost upfront – plus the diver can work more actual jobs.
Some jobs which require a human diver can actually be done under a diver’s direction but without the diver having to go into the water, or at least not having to go in as much. For example, hull inspections or damage surveys often involve putting eyes on the target, but don’t require any hands-on work. A diver reviewing an ROVs video feed can do just as good a job as if they had been in the water the entire time – but again, with much lower costs and no risk. Remember, risk costs money – in insurance premiums, in medical expenses, in training costs – and reducing risk is effectively the same as putting money back in your pocket.
Even hands-on work like underwater repair can be made more efficient and less stressful with intelligent use of ROVs. ROVs can be used to survey the worksite and get good information into the dive planner’s hands before anyone puts a foot in the water. And while the divers are actually working in the water, other staff can use ROVs to keep eyes on other areas of the work site, or to fetch tools and parts without a lengthy surfacing process.
We profit and grow when we see the potentials unlocked by technological change.
Divers who adapt to the technological innovation coming to the industry by adopting the new tools that ROV technology is making available are going to be able to do more work, to do it better, and to do it safer than they were doing it before. Adding ROVs to an existing dive business requires challenging some ideas about how the business should run, but it’s a change that will pay off.
The safety of our drinking water supply is a serious matter. By now everyone is familiar with the tragic situation in Flint, Michigan, where a decision to switch the municipal water system led to massive lead contamination in the drinking water. The Flint tragedy had numerous causes, but one lesson to be learned is that regular inspection of the physical water system is critically important. If the infrastructure of the Flint system had been adequately inspected, it is possible that officials would have been aware of the problem at an earlier date.
When it comes time to inspect a water system – whether a giant municipal potable water supply or a small private tank like a facility storage tank – remote operated vehicles (ROVs) offer a number of advantages over other methods.
In the pre-ROV era, tank inspections meant either sending a human diver into the tank (posing risks to the safety of both the water supply and the human diver) or draining the whole tank and inspecting it dry. Both of these approaches have serious drawbacks. Using ROVs as the centerpiece for a tank inspection strategy has some enormous advantages over the older method.
The Tank Doesn’t Need to be Drained
Draining a water tank is a wasteful and expensive process. A municipal potable water supply tank can be millions of gallons of water – even tens of millions of gallons. It’s rare for there to be any productive use for all that water being drained at once – it literally flows out into the sewers and is gone. Not only that, but the water system the tank was supporting is then left high and dry while the inspection takes place. ROVs permit the tank to be left filled and in service while the inspection is taking place, saving both time and money.
No Risk to Human Divers or the Water System
Human divers cost a lot of money. Training, equipment, insurance – the list goes on. If there’s a safety incident, the financial cost alone can be huge, to say nothing of the human cost. In addition, to send a human diver into a potable water system, the diver must be sterilized – a difficult, unwieldy and unpleasant process, and one which if done improperly can compromise the safety of the entire water system.
ROVs, on the other hand, are relatively inexpensive and, compared to a human life, completely expendable. Because they are small and mechanical, they are much easier to sterilize for use in a potable water environment. Best of all, ROVs don’t charge extra for working a long shift!
Low Barrier to Entry
Certified divers are skilled professionals and scarce in some locales. By comparison, becoming proficient in operation of the Aquabotix ROV is a matter of three days of practice with the vehicle. Divers require support teams, so a minimum of two people are going to be on the job site, but an ROV is a one-person operation. Aquabotix ROVs come complete with recording capability (allowing the operator to take video footage, snap photographs, and record data from onboard instrumentation) and can operate on battery power alone.
Built-In Data Gathering
Every measurement a human diver takes requires them to carry (and learn the operation of) another sensor or instrument. ROVs, on the other hand, can carry built-in sensor suites that have all of the needed data-gathering equipment for any given inspection mission. For example, thermal stratification (water forming temperature layers or clines) can prevent mixing of water in a tank, which can reduce the efficacy of chlorine or chloramines in disinfecting the water. ROVs carry temperature and depth sensors which will automatically record and report the temperature and depth throughout the vehicle’s inspection cruise, automatically producing an easily-read report showing problem areas. There are many other environmental sensors available for ROVs which can quickly collect enormous amounts of data that would take a human diver multiple dives, at great expense, to gather. For example, ROVs can carry a Cygnus NDT metal thickness gauge, allowing the vehicle to test the thickness of the tank wall at hundreds or even thousands of points during an inspection.
Increased Frequency of Monitoring
As become sadly evident in the case of Flint, a water system can develop problems very quickly. Because ROV-based inspections are so much less expensive and so much more convenient than diver or draining inspections, they can be performed at much shorter intervals. That means, for example, that a problem like Flint’s (which is expected to cost hundreds of millions of dollars to fix) might instead have been caught when it could have been fixed for a few million. Frequent inspections greatly increase the chance of catching minor problems while they are still minor.
ROV-based inspections of water systems, particularly water tanks, save water and money, reduce the risk to human life, increase the safety of the water supply, are easier for small municipalities and operations to do for themselves, and collect valuable data at a lower cost than other options. There will continue to be need for human divers in some applications, but ROVs greatly expand our ability to inspect, and to keep safe, our water systems.
Fire tanks are an important part of the infrastructure that supports firefighters around the globe. These tanks are found at residential, commercial, industrial and institutional sites. Some fire tanks are used to supplement a building’s available standard water pressure during a fire emergency, while others provide the direct water supply for a building’s internal sprinkler system.
Obviously, the condition of these tanks is a major part of a building’s fire safety plan.
There are a number of industry and regulatory standards for fire tank construction, installation, and inspection. In the United States, the National Fire Protection Agency has two important standards: NFPA 22, which establishes the requirements for the design, construction, installation, and maintenance of tanks and accessory equipment that supply water for private fire protection, and NFPA 25, which sets standards for the inspection, testing, and maintenance of water-based fire protection tanks and systems. Other industry standards include the Factory Manual (FM) standard and American Water Works Association (AWWA) standard.
These standards exist in a patchwork system of governmental, insurance, and industry mandates and policies, so it is difficult to make general statements about which regulations are going to apply to which facilities. As in real estate, a great deal boils down to “location, location, location” – where you are and what your facilities does will control what regulatory regime(s) you are subject to.
However, probably the single most widespread requirement is also the most onerous for tank owners, and that is the requirement for periodic inspections of the inside of the tank.
Inspections look at a wide variety of tank conditions, including (but not limited to) internal corrosion, the condition of suction inlets and vortex inhibitors, roof supports, vermin infestation, the condition of tie rods and liners, ultrasonic or electronic testing of tank wall thickness, dry film thickness testing, paint adhesion, and more. In addition, inspections are often also combined with repair work to fix problems that the inspection uncovers.
How often are tanks required to be inspected? In the United States, NFPA 25 sets a requirement for a complete internal inspection every five years, a fairly typical value. Each country has its own legal requirements, however, and it is important to check your own local laws and regulations to know the inspection interval.
Rules and regulations can change, sometimes very quickly, and those changes can have enormous impacts. For example, in Australia, the regulatory standard is known as AS1851, and it recently changed the inspection interval for fire tanks from every ten years to every year – a tenfold increase in required inspections! Given that Australia has approximately 20,000 water tanks, this is a massive increase in the inspection workload. Fortunately, the standard also permits the use of ROVs as an alternative to human divers for inspections, meaning that Australian tank inspection companies can now leverage their human divers with an ROV fleet. This will permit them to greatly increase the efficiency and decrease the cost of tank inspections.
Aquabotix ROVs make an excellent addition to any tank inspection service, providing new capabilities, reducing the cost of existing capabilities, and increasing the reach and flexibility of human divers.
The problem of seeing things underwater is one that has vexed divers and others who work in the water since time immemorial. Ordinary vision works OK, in the daytime or with artificial light, in shallow water, in good conditions – but fails spectacularly in poor light or when water conditions are murky or worse. The modern electronic marvel that let us “see” for thousands or even millions of miles through air and space – radar – is completely useless underwater; water is effectively a brick wall to the short electromagnetic wavelengths that radar employs. Yet it is extremely important that underwater craft be able to sense their surroundings; if your craft is unable to see what is around it, you will pay the price for your lack of vision.
Around the beginning of the 20th century, researchers realized that they could use sound waves to “see” underwater.
Unlike radar, sound waves propagate just fine underwater – in fact, they propagate underwater better than they propagate through the air. The first sonar-like devices were used to listen for icebergs; sonar technology advanced enormously during the First World War as a tool to listen for enemy submarines. Sonar still has extensive military uses, but today civilian sonar is the primary area of development.
Although in this post we will talk about “seeing” it should be noted that sonar does not actually produce a direct visual image. Many sonar control suites will translate the sonar data into a visual picture, and high-end sonars actually can produced simulated images that look very much like you are “seeing” what is out there – but the actual data is sound pulses being reflected back. Computers do much of the interpreting of that data stream, making it more accessible to people without advanced training in sonar interpretation.
Most remote-operated vehicles have the ability to carry sonar sets as optional equipment.
ROVs use sonar for a variety of purposes, from mapping the bottom of bodies of water to searching for items in the water.
There are three basic types of sonar available for deployment on an ROV:
Scanning sonar operates in a way that will be familiar to anyone who has ever seen a radar dish turning at an airport. The sonar emitter physically rotates, sending out a pulse of sound as it does so, and simultaneously listens for the echoes returning from any objects in the water. The rotational speed of a scanning sonar balances out the time between pulses and the time it takes for a returning pulse to come back to the sonar.
Scanning sonars do not provide a high degree of resolution. They are able to detect large objects (for example, pilings or ships) but lack the discrimination necessary to spot smaller objects, particularly when those objects are on the bottom or next to another object. Because there is only one beam, scanning sonars have no ability to see behind objects; if one object is behind another object in a line to the scanning sonar, the scanning sonar can see only the closer of the two. The strength of the scanning sonar is that it does cover an area of 360 degrees, although only from 10 to 20 degrees above and below the plane of the sonar.
Multibeam sonars (often referred to as “hydrophones”) are significantly more capable. A multibeam array has multiple sonar emitters, which are all digitally rather than manually moved, allowing for a much higher rate of scanning. A combination of hardware and software allows the multibeam sonar to sweep a wider area of the water – about 120 degrees in all directions. Multibeam sonars do not cover a 360 degree arc, however. They make up for this by having a higher degree of resolution than scanning sonars – at a hundred meters, a multibeam sonar can spot a diver in the water. At 10 meters it can distinguish arms and legs. Multibeam sonars are extremely good at looking in one direction at a time.
Side-Scanning sonars have two arrays, each of which has a sonar beam that traverses a 90-degree arc, one horizontally and one vertically. This means that they can see in almost every direction, except for straight up and down. Side-scanning sonars are used to collect data as an ROV moves through the water; unlike scanning and multibeam sonars, they do not provide information in real-time. Instead, they provide a “historical” view of what was there when the ROV was moving past a certain point. The advantage of side-scanning sonars is that they “see” almost everything, providing great resolution and covering an enormous area. Side-scanning sonars are suitable for wide-area searches for stationary objects (such as bodies or objects on the bottom of the body of water), surveying, and environmental monitoring.
The right type of sonar for your ROV will depend on the missions for that ROV. Each sonar type has advantages and disadvantages for various kinds of work. Aquabotix ROVs can be configured with any of these sonar types. As with other accessories, choosing the right tools for the job will go a long way towards ensuring that you get the best possible results.
One of the important elements in ROV mission performance is the quality of the visual information that the ROV passes back to the operator. Sending an ROV into the water lets a human being put eyes on the target, and those eyes need every well-lit pixel they can get.
What lets an ROV operator get the highest-quality underwater visual information back from his or her vehicle?
A significant component of video quality is the video format being used by the camera. For most of the 20th century, video cameras used either the NTSC or PAL standard. NTSC displays had (and still have) 480 lines of usable vertical resolution, while PAL used 576 lines. Both the NTSC and PAL formats had 4:3 pixel ratios, meaning that an NTSC picture is 640x480 (not coincidentally, the same screen size as the old VGA computer monitor standard) while a PAL picture is 758x576. These resolutions were adequate for the black and white and color TVs found in most homes up until around 2010.
Both PAL and NTSC are interlaced formats, meaning that every other scan line is refreshed at each frame (i.e., half the picture is refreshed in one frame, the other half on the next frame). This produces a smoother picture at reasonable frame rates, with the unfortunate downside of producing jitteriness during motion shots. Neither NTSC nor PAL would make good formats for underwater video for this reason, even if their low resolution was not an obstacle: an NTSC frame has only 307,200 pixels and a PAL frame has only 436,608.
Modern video cameras use one of the HD (high-definition) standards. The lowest form of HD is 720p, which provides 720 lines of vertical resolution with a progressive (non-interlaced) scan. This provides 921,600 pixels, which is a step up from NTSC or PAL but still leaves something to be desired.
The midrange HD standard is 1080i, which has 1080 lines of vertical resolution but unfortunately reverts to an interlaced display. This provides 2.07 megapixels per frame, but only 1.03 megapixels refresh with each frame, leaving the video subject to jerks and jittering. The highest HD standard is 1080p, which provides a full 1920x1080 2.07 megapixel frame without interlacing. 1080p is the best commercially-available picture format; 1080p video at 24 frames per second is the equivalent of watching a Blu-Ray DVD on an HDTV. 1080p at 24 frames per second is the gold standard for underwater video quality.
However, size is not everything, and there are other important elements to consider when maximizing underwater video quality.
One critical area is lighting. In many ROV applications, such as water tank inspection, there is no natural light at all, and even in open water the sunlight diminishes drastically with depth. At 10 meters down in crystal clear water, there is only about 25% as much light as at the surface and at 100 meters down there is only 0.5% as much light. Rough water and particulates in the water can make things even dimmer. Even if you have adequate natural light for your purposes, remember that water causes a distortion in the color spectrum; red light is absorbed most rapidly causing things underwater to tend strongly towards appearing blue or green. If your application needs accurate color, or if you need more light than is naturally available at your depth, then artificial lighting from the ROV itself will be necessary to get good video quality underwater.
The optical characteristics of the lens and the mechanical elements of the camera itself are also important in underwater video work. A wide-angle lens allows a very close focus on objects in the field of view, which means that the operator can get very close to the subject and still have a clear picture. A camera that can tilt and pan while the ROV hovers in one place can get even tricky shots into close focus. Of course, the maneuverability and ease of control of the ROV itself can be determining factors here – you have to be able to get the camera to the target, so an ROV that is easy to control is one from which it will be easy to get good video.
The combination of a high-quality video format, a high-yield lighting array, a well-designed optical system, and a maneuverable, flexible ROV will provide the best possible underwater video quality for any application.