Systematic investigation of the marine ecosystems of the biosphere is crucial in order to learn more about the lifeblood of our Earth. 70% of the planet’s surface is water, and less than 10% has been explored by humans. This immense marine environment offers unparalleled opportunities for scientific investigation, whether that be with the use of Automated Underwater Vehicles (AUV), Remotely Operated Vehicles (ROV), Human Operated Vehicles (HOV), or self-contained underwater breathing apparatus (SCUBA). There are many different modes of diving, these include free diving, SCUBA diving, Surface Supplied diving and atmospheric pressure diving
“Open circuit scuba is the most predominant method of scientific diving as it is widely available, lightweight and portable” (Heine, n.d.). The physiological boundaries of SCUBA include time restrictions and safe depth. A scuba diver must be efficient when investigating marine habitats in order to avoid over exertion. These factors/ boundaries can cause the observer-expectancy effect. Experience is also a limiting factor, as it is intrinsically important that a scientific investigatory dive be performed by experienced divers confident in preparing equipment (filling cylinders), getting kitted up and checking the kit of their dive buddy as well as their own (which takes a lot of planning and preparation), who must have the qualifications in order to perform the dive and a valid medical fitness certificate. Weather conditions, tides, underwater visibility (low visibility can result in entanglement) and currents can affect the quality of the dive as well as the data obtained from the survey. Other potential issues in collecting data include the attraction or deterrence of fish due to bubbles formed from open circuit SCUBA, and the disrupting of benthos (disturbing food and thus attracting fish). Certain fish can become familiar with divers which effects the data and estimation of fish density as they may not flee the area as expected at the divers arrival. Fish can be over or underestimated due to human error.
Remotely operated vehicles (ROVs) and automated underwater vehicles (AUVs) are identified as “unmanned underwater vehicles” and are used to explore the ocean. These submersible vehicles are momentous advances in marine technology. They give great advantage when studying an environment so hazardous. Both vehicles completely remove human risk, taking the diver out of the equation.
ROV’s, common in deep water trades (for example hydrocarbon extraction), are operated by crew on a vessel, and are tethered to the host ship. A tether management system (TMS) holds the ROV (on a smaller work-class model), or, on a larger work-class model, it is positioned on top of the ROV. The TMS controls the 300m buoyant tether in order to reduce cable drag in currents. An umbilical cable carries fibre optics (an energy source) and information (control) transmission in the form of data signals to the operator. A video camera is what most hydrographic ROVs are equipped with. Others may have a still camera, sonar, an articulating arm for cutting and/or object retrieval, and instruments to measure water temperature, clarity, density and light penetration. ROVs can be used for inspection and object identification surveys, construction and maintenance of below sea level development, location of shipwrecks, object recovery and hazardous mine clearing. Depths of 10668 meters can be achieved (unattainable by SCUBA divers who can reach 60 meters when technically trained). Day and night, ROVs can be used and they are indispensable for leading nocturnal surveys. SCUBA divers are able to dive at night, however due to colder temperatures, the need to move for warmth can cause overexertion and limit bottom time, however this is not always the case. “Studies show that divers may not perceive that they are cold and this degrades their mental performance” (Heine, n.d.) This, obviously, effects diver safety and collection of valid statistics.
AUV’s are programmable, requiring no control from an operator and have a variety of sensors, measuring the light, existence of microscopic life and concentration of elements. “AUVs are not as powerful as submersibles or ROVs” (Ransom and Wainwright, 2002), however, they are “not as effected by currents and weather conditions than ROVs are” (Staff, 1900). Vehicle size ranges from portable and lightweight to over 10 meters in length, the larger vehicles have greater endurance. Dead reckoning or an acoustic positioning system can be used to navigate underwater and it is propelled by a thruster unit or an electric motor and propeller. Rechargeable batteries power most AUV’s, and some use primary batteries at a much higher cost, for two times the endurance, allowing some AUV’s, such as the REMUS, 70 hours and 286 nautical miles of endurance. Others use semi-fuel cells which produce waste that must be disposed of securely. In comparison, a technical SCUBA diver at 30 meters may experience nitrogen narcosis, “a completely physiological response in the body” (Orr and Douglas, 2007), caused by gases at high partial pressure which is dangerous as it causes an anaesthetic effect on the diver who can become euphoric and unaware of potential danger, or can experience a “dark narc” and senses extreme stress. Below 66 meters, the diver is exposed to an intolerable hazard of oxygen toxicity when breathing compressed air. 100 meters may be reached when trained technically (maximum depth authorized for divers who have completed trimix diver certification with IANTD), a depth an AUV can reach with ease.
AUV communication with operators can be periodical or incessant through acoustic beacons or satellite signals. There are several types of AUV, reaching maximum depth of 6000 meters. Some examples are REMUS, Sentry and seaBED. As AUV’s are not controlled in the same way as ROV’s, this allows scientists to conduct other experiments while the AUV is collecting data elsewhere. AUV’s aren’t always fixed, making decisions due to environmental data. AUV’s are used for surveying missions and mapping (obstructions, rocks and wrecks). There is a current study in which AUVs in the Canadian Arctic pick up on the release of greenhouse gases from sea floor hydrates which has a monumental effect on global warming and therefore is extremely important.
Submersible technologies have been created to meet the challenges of the Ocean. With the use of these submersibles, many ecosystems have been exposed, for example environments under pressure and completely lacking light, as well as communities thriving in and around hydrothermal vents, despite extreme temperature and exposure to sulphur. Only submersibles allow humans to glimpse at abyssal depths. “Alvin” is a deep-sea submersible (HOV, or human operated vehicle), the first capable of carrying passengers and pilot. Nowadays, Alvin is able to reach a maximum depth of 14,764 feet and was constructed to survive the extreme pressure of the depths of the ocean, remaining submerged for 10 hours (the life support system will allow 72 hours). In comparison, a technically trained SCUBA diver is limited by the number of cylinders they may have, usually remaining submerged for 1 and a half hours to 2 hours. As well as this, increased pressure due to deeper diving can cause suit squeeze as air inside the suit reduces resulting in bruising and abrasions.
Whether moving through rugged areas, taking videos and photographs or hovering to perform scientific tasks, Alvin and other HOVs are able to perform despite temperatures or currents (unlike SCUBA divers effected by the elements). Five thrusters propel Alvin, and it is powered by Lead acid batteries. Over 13000 scientists have used Alvin to visit the seafloor, conducting chemical, geological and biological surveys. Since the discovery of hydrothermal vents in the Pacific Ocean (1977), Alvin has been used to discover 24 hydrothermal sites and 300 previously unknown species, for example 10ft red tipped tube worms.