WO2012129612A1

WO2012129612A1 - Method and system for surveying or monitoring underwater features

Info

Publication number: WO2012129612A1
Application number: PCT/AU2012/000331
Authority: WO
Inventors: Damian OGBURN
Original assignee: Ogburn Damian
Priority date: 2011-03-31
Filing date: 2012-03-30
Publication date: 2012-10-04
Also published as: AU2012234920B2; AU2012234920A1

Abstract

A method and system of surveying or monitoring an underwater feature (32), such as a reef, coral colonies (32a,b,c)..or other benthic habitat, includes using a remotely operated underwater vehicle (ROV) (12) tethered to a surface vessel (14) by a tether (16) incorporating discrete positional coordinate determination and/or relay means (40). The ROV (12) is able to be controlled by a controller (28) to revisit the same positional coordinates of one or more parts of the underwater feature because the tether device provides to the surface vessel to record the unique positional coordinates of the part(s) and the ROV is thereafter able to be accurately repositioned at the part(s) at a later time or date. This aids accurate ongoing surveying or monitoring of a feature for changes.

Description

METHOD AND SYSTEM FOR SURVEYING OR MONITORING UNDERWATER

FEATURES

TECHNICAL FIELD

The present invention relates to a method and system for surveying or monitoring underwater features, such as chemical or material plumes, underwater objects, sites or habitats, including oil and gas installations, flooded caves or cave systems, undersea topography, sunken vessels, benthic habitats, or particularly coral colonies.

The present invention also relates to a method and system for mapping a boundary of a benthic habitat.

BACKGROUND

Regular or repeatable surveying and monitoring of underwater features is challenging. Underwater features include, for example, subsea topographic features, benthic habitats, undersea installations and equipment, sunken vessels, the underside (hull(s)) of vessels, flooded caves and outflows emptying into water. Being able to identify an underwater feature, perhaps map it, and, at a later time, revisit that feature with positional accuracy is known to be difficult. Such surveying and monitoring is often required when environmental impact surveys need to be carried out prior to, during and/or after subsea drilling, excavation, installation work or when dredging is conducted. Environmental impact or likelihood of environmental impact from chemical plumes and/or plumes of suspended solid material at sea often also need to be assessed.

As an example, monitoring the health of benthic habitats, in particular coral colonies in tropical and sub-tropical areas, is a typical requirement to obtain environmental approval for marine dredging programs. Live coral are known to be negatively affected by sedimentation and therefore variability in the health of coral colonies may be used as an indicator of the impact of dredging activities on the marine environment.

Surveying and monitoring will hereinafter largely be described, in relation to known applications and the present invention, with reference to monitoring of coral colonies. However, it will be appreciated that other subsea sites and features may be surveyed and/or monitored in accordance with the present invention. For example, as mentioned above, the present invention is applicable to diverless surveying and/or monitoring of underwater chemical or suspended solid material plumes, underwater objects, sites or habitats, including subsea oil and gas installations, flooded caves or flooded cave systems, undersea topography, sunken vessels, benthic habitats, and coral colonies. Chemical plumes may come from hazardous chemicals or waste material present in the water (such as discharge from ships, chemical spills, leakage or discharge from installations, or from onshore outlets into the water). Plumes of fine particulate materials suspended in the water may come from dredging operations, seabed disturbance, drilling or installation of subsea equipment etc. Plumes may, of course, contain a combination of solid and chemical matter.

It has been realized that the present invention is particularly applicable where underwater conditions create locating and/or positioning problems, such as in surging, bubbly or turbulent water and/or in poor visibility conditions (as in sandy or cloudy water caused by disturbance of the sea bottom or sediment). It has been found in developing the present invention that such conditions result in intermittent, poor or no communication for line of sight' communications, such as visual diver based systems or echo-sounder systems using sonar. Accurately locating/relocating and positioning/repositioning at a site of interest can become extremely difficult or impossible with such known systems. For example, known ultra short baseline (USBL) systems rely on an acoustic 'ping' to locate and position a remotely operated underwater vehicle (ROV). Such line of sight systems and methods are unreliable in difficult weather or water conditions, such as surging, turbulent or cloudy water. Accurately locating or positioning an ROV at or to a required position can become impossible.

USBL (also sometimes called Super Short Base Line - SSBL) is a method of underwater acoustic positioning. A transceiver mounted under a ship communicates with a transponder/responder on the seafloor, on a towfish, or on a ROV. A computer is used "topside' to calculate position of the seafloor transponder/responder, towfish or ROV from the ranges and bearings measured by the transceiver. An acoustic pulse is transmitted by the transceiver and detected by the subsea transponder/responder, which replies with its own acoustic pulse. This return pulse is detected by the transceiver under the vessel. The time from transmission of the initial acoustic pulse until the reply is detected is measured by the USBL system and is converted into a range. To calculate a subsea position, the USBL calculates range and angle from the transceiver to the subsea transponder/responder. Angles are measured by the transceiver, which contains an array of transducers. "Phase-differencing" is used to calculate the angle to the subsea transponder/responder.

Diver-based monitoring of individual tagged coral colonies prior to and throughout the duration of a dredging program is commonly employed. Divers collect observational data on specific attributes related to coral health, including percentage cover of live, dead or bleached coral, occurrence of broken or damaged coral, incidence of predators such as the crown-of-thorns starfish, and incidence and percentage cover of epiphytes, such as algae.

The accuracy and precision with which these response variables are estimated from sampling is essential. Typically, baseline data collection is obtained by collecting observational data along permanent transects which have been established in and around the monitored area. Up to 15 sites spaced up to 30 km apart may be selected, and up to 60 individual coral colonies within each site may be physically tagged with intrusive pickets or chains to facilitate relocation of the colonies by the divers over the duration of the monitoring period. Such physical tagging methods may contribute adversely to the health of the coral colonies.

There is a need to develop surveying and monitoring methods that are independent of divers. Occupational health and safety issues associated with decompression illness and risk of harm from sharks and jellyfish are a concern. Moreover, activities undertaken by divers may be constrained by operational conditions adversely affected by weather, sea state, available light, water turbidity and limitations in relation to depth and time spent at depth. Sea surge, strong currents, turbulent conditions, sediment laden water, can each contribute to poor visibility and danger to a diver. Turbidity includes reference to the amount of suspended solids in water, which may or may not eventually settle out over time. Such conditions make accurately relocating or maintaining the diver(s) at the site of interest extremely difficult. If the diver(s) is/are required to leave the site of interest, and perhaps return to their vessel, finding the exact location they were previously at requires time (of which divers only have a limited amount at depth or due to air supply limitations), improved conditions (which may deteriorate again) and some way of locating their last position.

It has also been realised that repeatability of landing' at exactly the same monitoring zone(s) as previously monitored is often not achievable for divers. Whilst they may mark a site, such as with marker posts pushed into the seabed, to later return to the same site, those marker posts may be washed away by the current or fall over and become buried in the seabed. Also, if the diver does not follow exactly the same protocol for gathering images as previous monitoring surveys, the image data will not be consistent from one survey to the next, and improvement or degredation of the site may become impossible to determine accurately.

An alternative means of collecting observational data in benthic habitats involves the use of remotely operated vehicles (ROV) or drop camera systems. Both systems may be safely employed across a wide range of depths, turbidity, light, weather and sea-state conditions, and have no underwater time limitations.

In general, the drop camera is connected to a vessel by a tether and drifts approximately 0.5 to 0.75 in over the seabed and takes a sequence of high resolution still images along short transects across multiple random transects. It is not possible for a drop camera system to specifically access, relocate and monitor individual tagged corals in a study area.

ROV systems, on the other hand, are capable of accessing underwater features, such as individual tagged corals, and collecting high quality images (such as of these coral colonies). Obtaining real-time positioning data relating to the ROV systems, however, has been problematic. Locational fixes on ROV systems have been previously obtained by integrating information about vessel location, motion sensor information for pitch, roll and heading corrections and acoustic camera positioning. The cumulative effect of combining these integrated readings has been an increase in the errors associated with taking a precise locational fix. Global positioning systems (GPS) may be fixed to a ROV but since a GPS reading cannot be made when the ROV is submerged, the ROV has been forced to rise to the sea surface to take a precise locational fix by GPS and then submerge again to continue collecting observational data.

Accordingly, there is a need to provide a means of collecting data, such as observational data in benthic habitats, observational data on underwater features generally and/or data relating to presence/absence of chemical(s) and/or solid material in the water, with a capability for determining precise and real-time location of the ROV and preferably of the underwater feature(s), such as a benthic habitat which is being monitored.

Such a system also provides material advantages in relation to mapping the boundaries of benthic habitats.

Further applications of the present invention are applicable to sensing presence or absence of chemicals or solid material in the water. Such applications can be used in determining water quality and risk or presence of environmental impact.

Currently, underwater surveying is often undertaken using a multi-beam echo-sounder or a side-scan sonar system.

A multi-beam echo-sounder is a device typically used by hydrographic surveyors to determine the depth of water and the nature of the seabed. Most modern systems work by transmitting a bread acoustic pulse from a specially designed transducer across the full swath across-track then forming a receive beam that is much narrower (around 1 degree depending on the system) to establish a two way travel time of the acoustic pulse. If the speed of sound in water is known for the full water column, the depth and position of the return signal can be determined from the receive angle and the two-way travel time. In order to determine the transmit and receive angle of each beam, a multi-beam echo-sounder requires accurate measurement of the motion of the sonar relative to a Cartesian coordinate system. Typically the measured values are heave, pitch, roll and heading. Higher frequency systems used for habitat mapping in shallow water have also been developed, with such systems widely used for shallow water hydrographic surveying in support of navigational charting.

Multi-beam echo-sounders are also commonly used for geological and oceanographic research, and since the 1990s for offshore oil and gas exploration and seafloor cable routing. Side-scan sonar is a category of sonar system that is used to efficiently create an image of large areas of the sea floor. This tool is used for mapping the seabed for a wide variety of purposes, including creation of nautical charts and detection and identification of underwater objects and bathymetric features. It may be used to conduct surveys for maritime archaeology; in conjunction with seafloor samples it is able to provide an understanding of the differences in material and texture type of the seabed. Side-scan sonar imagery is also a commonly used tool to detect debris items and other obstructions on the seafloor that may be hazardous to shipping or to seafloor installations by the oil and gas industry. In addition, the status of pipelines and cables on the seafloor can be investigated using side-scan sonar. Side-scan data are frequently acquired along with bathymetric soundings and sub-bottom profiler data.

Thus, providing a glimpse of the shallow structure of the seabed. Side- scan sonar is also used for fisheries research, dredging operations and environmental studies. It also has military applications including mine detection. Side scan uses a sonar device that merits conical or fan-shaped pulses down toward the seafloor across a wide angle perpendicular to the path of the sensor through the water, which may be towed from a surface vessel or submarine, or mounted on the ship's hull. The intensity of the acoustic reflections from the seafloor of this fan-shaped beam is recorded in a series of cross-track slices. When stitched together along the direction of motion, these slices form an image of the sea bottom within the swathe (coverage width) of the beam. The sound frequencies used in side-scan sonar usually range from 100 to 500 kHz: higher frequencies yield better resolution but less range.

Both of the above described systems obtain information about undersea features, including benthic habitats, from extensive data collected over swathes of up to 200m. Determination of the boundaries of a benthic habitat can only be made after time-consuming analysis of the data in which a great deal of the collected data may be either redundant or misleading.

Whilst the use of ROVs alone does mitigate risk to divers, ROVs have bene found to be difficult to maintain in position, or locate a particular site, when attempting to survey or monitor an underwater feature in strong sea swells, turbulent water, turbid water or currents. A problem has been identified in known and currently adopted methodologies for monitor undersea features, particularly the health of coral reefs. Such monitoring is typically conducted prior to dredging programs. Historically, such monitoring has been achieved with the use of divers taking repeat time series of photographs of sentinel locations, usually 50-400 coral colonies at each of a range of impact and reference sampling areas relative to the expected or actual dredge plume of a dredging program. A current transition in monitoring methodology is to adopt diver-free methods using ROVs equipped with instrumentation including camera systems and coupled to a tether linked to a 'mother vessel' through which the ROV pilot drives the ROV and operates the instrumentation on the ROV from the mother vessel. These underwater sentinel points are often up to at least one hundred metres from the vessel in shallow unnavigable water and this adds a large degree of complexity and time to repeat sampling (over a period of weeks to years -depending on dredging/impact activities) at these sampling locations. ROVs are safer and cheaper to operate than use of divers in such coral health monitoring programs.

An ultra short baseline (USBL) differential GPS navigation system (which provide sub metre precision on a global geo-reference satellite system) has been used for navigation/location of the ROV. However, it has been found that the USBL system, which operates on 'line-of-sight' between the USBL transducer fitted under the hull of the mother vessel and the USBL responder attached to the ROV has significant problems in locating the ROV GPS reference points on coral colonies and reef systems. This problem is understood to be due to interference in the USBL signal resulting from complex topology typically encountered on the shallow reef systems, and interference due to entrained bubbles from wave wash and surge also typically encountered on shallow reef systems. Turbidity from dredge plumes would also create similar USBL signal interference. Consequently the ROV may not be successfully remotely navigated to a predetermined reference point (sampling location - typically a coral colony) without the use of markers (e.g. steel picket) at the reference point. The ROV therefore has to be directed and propelled ('swum') to the location with the ROV operator using visual sighting to locate the marker point(s) through the ROV video system. Like divers who typically swim through a reef searching for the marker posts (or 'star' pickets) that locate each of the sentinel coral colonies, the ROV is used in a similar search pattern. However, due to the fixed forward looking vision system this search and locate system using star pickets as markers is much slower using an ROV compared to a diver. In addition, it still requires the use of intrusive star picket marker posts and chain markers which must be installed, maintained and removed using divers.

In addition, it has been found difficult to identify precise GPS reference points (and therefore a map) for each of these underwater locations because a precise fix (<1 m precision in x,y coordinates) of the point may not be obtained (GPS does not work underwater.) One attempted solution to this problem has been to provide a GPS transmitter fitted to a buoy at the water surface attached to a rope to the ROV, but this does not provide a precise relocation system for the actual position of the submerged ROV.

The present invention seeks to overcome at least some of the aforementioned disadvantages.

SUMMARY OF THE INVENTION

With the aforementioned in mind, an aspect of the present invention provides a method of surveying or monitoring an underwater feature, the method including: a) providing a remotely operated underwater vehicle (ROV) with data capture means capable of recording and/or transmitting data to a base station remote from the ROV; b) determining and transmitting real-time positional coordinates of the ROV when underwater to the remotely located base station; c) controlling the ROV to arrive at a desired set of positional coordinates in response to received real time positional coordinates of the ROV; d) capturing data relating to one or more parts of the underwater feature using sensing or detection means or image capture means associated with the ROV; e) recording and/or transmitting the captured data to the base station.

The method may also include identifying one or more parts of the underwater feature to survey or monitor using the ROV, each part having unique positional coordinates. Identification may be visual, such as by camera viewing one or more particular characteristics of the underwater feature. Identification may be electronic, such as by detecting proximity to or presence of one or more beacons, tags or markers. The positional coordinates of the ROV may be compared to the unique set of positional coordinates of the one or more parts of the feature to be surveyed or monitored, which can help in locating the ROV relative to the feature and its surroundings.

The method may further include processing recorded and/or received data of the part or parts to generate data on sensed and/or observed attributes of the underwater feature. Controlling the ROV can locate one or more of the parts of the underwater feature.

The method may include connecting the ROV electronically via a tether device to a controller/base station, the tether device incorporating a series of positional coordinates relay devices. Such a tether can advantageously be used to relay position/location data to/from the controller, the data relating to the position/location of the ROV, and preferably to unique positional coordinates of the ROV and/or one or more relays (electronic transceivers or 'nodes') of the tether.

Identifying one or more underwater features includes, but is not limited to, identifying physical and/or chemical features or characteristics of the underwater feature. This can include presence or absence of one or more chemical elements or molecules, such as acid/alkali, toxic waste, chemicals from a process platform outlet, hydrocarbons (e.g. crude oil leakage). Physical features or characteristics can include, but not be limited to, presence or absence of solid matter, living organisms, topographic features, and underwater installations and equipment.

For example, ROV may convey one or more chemical ad/or material sensors to detect presence of chemicals and/or solid materials within the water (physico-chemical data). Thus, the ROV may be configured to detect a chemical signature, such as change in pH (acidity or alkalinity), presence of hydrocarbons, presence of toxic chemicals.

The data may include image data and/or turbidity data. Turbidity is the cloudiness or haziness of a fluid caused by individual particles (suspended solids) that are generally invisible to the naked eye, similar to smoke in air. Fluids can contain suspended solid matter consisting of particles of many different sizes. While some suspended material will be large enough and heavy enough to settle rapidly to the bottom of the container if a liquid sample is left to stand (the settable solids), very small particles will settle only very slowly or not at all if the sample is regularly agitated or the particles are colloidal. These small solid particles cause the liquid to appear turbid. Turbidity in seawater can be a sign of discharge of matter from a vessel, oil/gas installation or outflow from an onshore outlet to sea, from a disturbed seabed or dredging. All of these degrade the quality of the water, sometimes only visually but often with an environmental impact on marine life and benthic habitats.

The positional coordinates of the ROV may be relayed via a tether device. The tether device may incorporate a series of positional coordinates relay devices. These relay devices are capable of acting as 'nodes' to relay to another relay device the positional coordinates of and received from yet another relay device or from/to the ROV. Thus, positional data may be daisy chained from one relay device to another until finally sent to the base station.

Controlling the remotely operated underwater vehicle may include locating one or more of the parts of the underwater feature by comparing the real-time positional coordinates of the ROV and the unique set of positional coordinates of the one or more parts of the feature to be surveyed or monitored.

Surveying or monitoring physico-chemical characteristics of the underwater feature may include the steps of detecting physico-chemical characteristics in the water using one or more sensors associated with the ROV and transmitting to the base station the positional coordinates of the detected physico-chemical characteristics.

Positional coordinates may be used to create a map/plot/estimate of a physical extent of the physico-chemical characteristics in the water. The method may include returning and repositioning the ROV to selected ones of the positional coordinates based on the previously obtained said positional coordinates. The method may further include revisiting previously surveyed or monitored parts of the underwater feature to subsequently resurvey or re-monitor at a later time by repeating steps obtain updated data, such as image or sensor data, of the one or more parts of the underwater feature.

It will be appreciated that the underwater feature may preferably be a reef or one or more coral colonies.

A system of one or more forms of the present invention provides a remotely operated underwater vehicle (ROV) having or connected to a geo- referenced position determination means, and a tether connecting the ROV disposed underwater to a surface vessel, the tether including relay means to transmit real time geo-referenced positional coordinates of the ROV underwater to or from an ROV control system on the vessel.

Advantageously, the system including the tether coupled to the ROV is able to repeatably relocate the ROV to one or more underwater GPS points of an underwater feature, such as a ref or coral colony, in geo-referenced x,y,z coordinates where conventional USBL system fails.

Repeatable ROV positioning is useful in survey and monitoring programs including, for example:

^■ coral and marine health monitoring programs;

^■ mapping and relocating sentinel coral sampling sites (sentinel colonies);

^■ high definition image acquisition in dredging programs;

^■ environmental monitoring of sensitive seafloor areas in harbour development programs;

^■ waste water treatment outlets where high definition image acquisition is required;

^■ monitoring by high definition image acquisition of seafloor features, such as landforms, seagrass sites and other ecological communities for incremental changes in sedimentation due to dredging or other activities;

^■ geo-referenced mapping of water quality parameters such as a plume dispersion is required in x/y/z coordinates; ^■ geo-referenced mapping and characterisation of boundaries of underwater landscapes/ habitats/ infrastructure by high definition image acquisition;

^■ inspection programs for areas where turbulence or other interferences to USBL may occur, such as infrastructure integrity inspections for pylons and other marine/freshwater infrastructure such as aquaculture facilities, artificial reef systems, dams and pipelines;

^■ vessel hull inspections for introduced marine pests (IMPs) including mapping location of IMPs on moored vessels;

^■ IMP inspection and mapping in harbours and other identified risk areas for presence, distribution and change in IMPs and native infauna/inflora;

^■ locating items of interest underwater and mapping with geo-referenced coordinates in areas where USBL will not or is thought unlikely to work effectively;

^■ underwater cave exploration;

■ internal inspection of large pipeline/reticulation systems;

^■ Water quality detection (such as when seeking to detect presence of sewage, dredging plumes, discharge from vessels or oil/gas installations)

It will be appreciated that the preset invention need not be for the purposes of collecting images, though such image data acquisition is encompassed within the scope of the present invention. Data may be acquired from one or more sensors associated with an ROV. Such sensors may acquire physico-chemical data. One or more embodiments of the present invention is/are advantageous in precision underwater relocation of ROV for environments where interference with conventional USBL systems that may be encountered.

The tether may include multiple devices to relay geo-referenced position coordinates of the ROV sequentially from one to the other between the ROV and the surface vessel. Alternatively, or in addition, the multiple devices may each provide position and/or movement data of the tether and/or the ROV to a control system.

A further aspect of the present invention provides a method of positioning a remotely operated underwater vehicle (ROV) to an underwater position,

Controlling the ROV is capable of being repeated at a later period or periods of time to re-locate the one or more coral colonies and then recording and/or transmitting further images of the one or more coral colonies at periodic intervals of time.

In accordance with another aspect of the invention there is provided a system for monitoring coral colonies, the system comprising:

a remotely operated underwater vehicle provided with a camera for recording and/or transmitting images to a remotely located base station and a means to determine and transmit real-time positional coordinates of the remotely operated underwater vehicle to the remotely located base station, said base station being provided with a control system for propelling and locating the remotely operated underwater vehicle to coincide with positional coordinates of the coral colonies in response to received real-time positional coordinates of the remotely operated underwater vehicle, and a system to process recorded and/or received images of the coral colonies to generate data or the observed attributes of the coral colonies.

In accordance with a second aspect of the invention there is provided a method of monitoring coral colonies, the method comprising:

providing a remotely operated underwater vehicle with a camera capable of recording and/or transmitting images to a remotely located base station and a means to determine and transmit real-time positional coordinates of the remotely operated underwater vehicle to the remotely located base station, providing the remotely located base station with a control system to propel and locate the remotely operated underwater vehicle to a desired set of positional coordinates in response to received real-time positional coordinates of the remotely operated underwater vehicle, selecting a plurality or coral colonies to observe, each coral colony in the plurality of coral colonies having a unique set of positional coordinates, controlling the remotely operated underwater vehicle to locate one or more of the coral colonies, by coinciding the real-time positional coordinates of the remotely operated underwater vehicle and the unique set of positional coordinates of the one or more coral colonies, recording and/or transmitting images of the one or more coral colonies to the remotely located base station, and processing recorded and/or received images of the one or more coral colonies to generate data on observed attributes of the coral colonies. In at least one embodiment of the present invention, the remotely operated underwater vehicle (ROV) is controlled to locate at least one underwater feature, such as one or more coral colonies, and recording and/or transmitting data (such as images) relating to the feature(s). The method is capable of repeating data captured at repeated or regular intervals over a time period, whereby the data recorded and/or received is processed to generate data on variation, presence or absence of observed/detected attributes..

For example, in one embodiment of the present invention, controlling the remotely operated underwater vehicle (ROV) to locate the one or more coral colonies and recording and/or transmitting images of the one or more coral colonies is repeated at regular intervals over a predetermined period, whereby the images of the one or more coral colonies recorded and/or received at regular intervals over the predetermined period may be processed to generate data on variation in observed attributes of the coral colonies over the predetermined period.

In accordance with an alternative aspect of the invention there is provided a system for mapping a boundary of a benthic habitat, the system comprising: a remotely operated underwater vehicle having a frame to which is attached a camera for recording and/or transmitting images of the boundary or the benthic habitat to a remotely located base station and a means to determine and transmit real-time positional coordinates or the remotely operated underwater vehicle to the remotely located base station, said base station being provided with a control system for propelling the remotely operated underwater vehicle along the boundary of the benthic habitat in response to collected and/or received images of the boundary of the benthic habitat, and a system to process collected and/or received images of the boundary of the benthic habitat and the real-time positional coordinates of the remotely operated underwater vehicle to generate a representation of the positional coordinates of the boundary of the benthic habitat.

In accordance with a further aspect or the invention there is provided a method of mapping a boundary of a benthic habitat, the method comprising: recording and/or transmitting images of the boundary of the benthic habitat to a remotely located base station with a camera attached to a frame of a remotely operated underwater vehicle, propelling the remotely operated underwater vehicle along the boundary of the benthic habitat in response to the collected and/or received images of the boundary of the benthic habitat, transmitting real-time positional coordinates of the remotely operated underwater vehicle to the remotely located base station as the remotely operated underwater vehicle is propelled along the boundary of the benthic habitat, and processing collected and/or received images of the boundary of the benthic habitat and the real-time positional coordinates of the remotely operated underwater vehicle to generate a representation of the positional coordinates of the boundary of the benthic habitat.

BRIEF DESCRIPTION OF THE FIGURES

Figures 1a and 1 b are schematic representations of a system for monitoring underwater features, such as coral colonies, in accordance with an embodiment of the present invention;

Figure 2 shows a method of monitoring underwater features, such as coral colonies, in accordance with an embodiment of the present invention;

Figure 3 is a schematic representation of a system for mapping a boundary of an underwater feature, such as a benthic habitat, in accordance with one embodiment of the present invention;

Figure 4 shows a method of mapping a boundary of an underwater feature, such as a benthic habitat, in accordance with an embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention broadly relates to a method and system for monitoring coral colonies, and a method and system of mapping a boundary of a benthic habitat.

Figures 1 a and 1 b show schematic representations of one embodiment of a system of monitoring coral colonies, including a remotely operated underwater vehicle (ROV) 12 connected to a remotely located base station 14 by an umbilical line 16 which supplies power and control functions to the ROV 12. In general, the remotely located base station 14 is located on a vessel, such as a survey vessel. In a preferred embodiment. The ROV 12 has a submersible weight (with full ballast set) of less than 10 kg, with dimensions within the range of 1200mm x 1200mm x 1200mm, maximum speed of up to 5 knots, depth rating of down to about 300m, and a positioning accuracy along its x,y,z axes of +/- 2m to +/- 0.1 m.

The ROV; 2 is provided with data capture means, for example a camera 20. The camera 20 may comprise a still camera and/or a video camera. Other data capture means can be provided, such as at least one sensor 42 for detecting presence and/or concentration of physico-chemical characteristics in the water. The camera 20 may be digital and/or high definition. The camera 20 may be capable of recording still or moving/movie images. The recorded images may be stored on a data storage device, such as a hard drive or memory stick associated with the camera 20. Additionally, or alternatively, the camera may be capable of transmitting images. The term 'images' as used herein may refer to still images or video footage. The ROV 12 may also support lighting, lasers and other sensors. It will be appreciated that the umbilical line/tether 16 may transfer data between the ROV and base station, or may also include supply of control functions to anyone or more of the carrera 20, lighting, lasers and other sensors, and the ROV. Additionally, the umbilical line/tether 16 may behave as a conduit for data (images, sensed parameters/characteristics of physical and/or chemical matter in the water) transmitted from the camera 20 to the base station 14.

The ROV 12 is also provided with a means 22 to determine and transmit real-time positional coordinates of the ROV to the base station 14. Suitable examples of said means include, but are not limited to, an ultra short baseline system (USBL) device, a tether-based positioning system device, which preferably includes a series of positional coordinates relay means along the tether 16, or a Doppler velocity log system device.

The USBL device uses a spread spectrum acoustic ultra short baseline range/bearing tracking system which employs a magnetic compass and pitch/roll sensor built into a transducer supported by GPS and heading/attitude sensors positioned on a surface vessel. The USBL device may be battery powered and independent from the umbilical line/tether 16. The range accuracy of the USBL device may be about +1- 0.2m and the bearing accuracy of the USBL device may be about +/- 3 degrees. While the USBL device may be suitable for use at depths and ranges of up to 1000m, the inventors have found that in some conditions, in particular in shallow waters such as sometimes found in coral reefs, the ability of the USBL device to determine and transmit real-time positional coordinates of the ROV 12 may be compromised by interference from reef projections, the wash of propellers and jets, or waves generated by the vessel or the reef.

The means 22 to determine and transmit real-time positional coordinates of the ROV 12 to the base station 14 may comprise a tether-based positioning system device. The tether-based positioning system device comprises a tether interconnecting the ROV 12 to the base station 14, wherein the tether incorporates a plurality of orientation sensors spaced at regular nodes along the length of the tether which communicate the real-time positional coordinates of the ROV 12 and the tether to the base station 14. In general, the tether-based positioning system device is powered by the base station 14. The tether may be about 40m to about 200m in length and operational down to about 300m depth. Positioning accuracy may be -/-/-2.0m to +/-0.1 m, depending on the tether deployment configuration. An illustrative example of a suitable tether-based positioning system device is the 'Smart Tether' (TM) provided by KCF Technologies. Such a tether 16 arrangement includes a series of relay means 40 (e.g. sensor nodes) incorporated within and along the tether. The 'nodes' use acceleration, magnetic, and rate-gyro sensors to measure orientation, and to determine and monitor the position of an ROV and also the tether itself. Such movement and position data is transmitted to a control system at the surface vessel, and is displayed on a computer screen in real time. Such a tether arrangement, together with a survey or monitoring regime, brings a solution to diver free coral/reef monitoring where known previous methods and systems are ineffective under the conditions discussed above.

This tether is a non-acoustic (e.g. USBL) underwater positioning system with a series of embedded sensor nodes. Being a non-acoustic system the tether is not prone to problems with acoustic reflections, noise (surging, bubbles etc.), or obstructions. Sensor nodes are spaced along the tether and electrically connected to each other in series. Each node contains a pressure sensor to be able to determine its own 3D orientation in space as well as its depth underwater, and a tri-axial accelerometer and a magnetometer. The nodes are fixed to the tether in water proof housings, preferably at specified distances between each node. A cable modelling algorithm approximates the shape of the cable between each node and builds up the tether shape, and thus determines the ROV position relative to the launch point. Geo-locating the launch point using a GPS receiver enables calculation of the relative displacement of the ROV to provide the absolute values for latitude and longitude coordinates of the ROV. The ROV has an end node in the chain to provide calculation of the heading of the ROV needed for communication and piloting. Understanding the entire tether shape also provides additional information to avoid entanglements or unwanted tether contact with sensitive subsurface features. Software gives the controller real-time feedback on the location of the ROV by calculating position values about five times per second.

The ROV can include one or more sensors 42 to detect presence and/or amount/concentration of chemicals and/or particulates in the water. For example, water pH variations may be detected and mapped. The sensor(s) may detect changes in turbidity. Turbidity may be detected and mapped.

Regarding the relay devices/means or 'nodes' (also termed 'positional coordinate determination means'), the tether preferably has such nodes 40 spaced along the tether from at or adjacent the launch point/control at the vessel or base station 'topside' (i.e. at the surface of the water) down to the ROV. The ROV preferably has a relay device(s)/means to communicate with the next 'node' along the tether. The figures (particularly Figure 1 a, Figure 1 b and Figure 3) show examples of this daisy chaining of communication. Positional data communicated along the tether may be cumulative i.e. one 'node' passing on its positional data and the positional data of the nodes before it in regard to the direction of travel of the data. Preferably data is transferred in both directions by the nodes along the tether. Alternatively, data transfer may be one way, preferably from the ROV to the base station. Control of the ROV can be by a separate umbilical tether carrying control cabling and signals, as well as acting as a physical tether to retrieve the ROV. The umbilical tether and the tether carrying positional data can be held together so as to form a single, yet coaxial, tether. In one embodiment the tether carries both control cabling and the positional data transfer nodes. This configuration enables calculation, using the algorithm or software, of the total shape of the tether along substantially its entire length from the ROV to the launch point and hence calculate the location of the ROV relative to the launch point, base station or vessel.

A Doppler velocity log system device uses acoustic signals to bounce off the bottom (or a reference layer of water) and can determine the velocity vector of a subsea vehicle moving across the sea floor. This information can be combined with a starting fix, compass heading, and acceleration sensors to calculate the position of the vehicle.

The base station 14 may be provided with a control system 24 to control and propel the ROV 12. System 24 may comprise a screen of a laptop 26 onto which, the transmitted images of camera 20 are displayed in real time, and a human interface device (HID) in the form of a joystick for example, may be used to control the movement of ROV 12 and propel ROV to a desired location in response to the received images of camera 20. Additionally (or alternatively) the laptop 26 may display the real-time positional coordinates or the ROV 12 transmitted by the base station 14 by the means 22 to determine and transmit real-time positional coordinates of the ROV 12, and HID 28 may be used to control the movement of ROV 12 and propel ROV 12 to a desired location in response to the received real-time locational coordinates of the ROV 12.

The laptop 26 may also display the output of sensors and may also display any other pertinent local information such as time and date. Laptop 26 may also save transmitted images, transmitted real-time locational coordinates, sensor and local data on its hard drive, CD, DVD, or an alternative electromagnetic recording device, external or otherwise. HID 28 is used to control the movement of the ROV 12 and propel tile ROV 12 to a desired location in response to images received from camera 20 and/or from real-time locational: coordinates received from said means 22. In a preferred embodiment, a 3D HID 28 is used. Forward and backward motion of the HID 28 may be used to control the angle of rotation of the ROV's 12 propellers/thrusters, with the neutral position of HID 28 corresponding to a horizontal orientation of the propellers. Depth of the ROV 12 is controlled by pushing the HID 28 forward to cause the ROV 12 to descend, and conversely, pulling the HID 28 backward causes the ROV 12 to rise toward the surface. HID 28 also has a throttle lever, which moves between off (no thrust) and on (full thrust). The system 10 also includes a system 30 to process images received of the coral colonies to generate data on observed attributes of the coral colonies. Various observed attributes may be used as indicators of coral health for reactive monitoring and long-term coral monitoring purposes. Such observed attributes for coral monitoring include, but are not limited to, percentage cover of live coral, bleached total, diseased coral, dead coral, broken coral skeleton, macro-algae, sediment. Additional observed attributes in relation to dead coral may include incidence or percentage cover of borer, crown of thorns starfish, turf algae, Drupella sp. sponge, other invertebrates, and macro-algae. Additional observed attributes which comprise indicators of stress include, but are not limited to, incidence or percentage cover of mucous and pigmented tissue.

The system 30 may comprise one or more computer programs to execute image analyses, statistical analyses, and power analyses to generate data or. observed attributes of the coral colonies.

One example of a suitable computer program to execute image analyses comprises the Coral Point count with Excel Extensions program. In this image analysis program, in respect of a received image, the smallest box that encompasses a focal coral captured in a landscape orientation may be drawn with a plurality of points (eg. 64 points) then randomly allocated within this sampling box area. Points falling outside the perimeter of the colony are generally excluded from the analysis. While the points on the coral colony are scored according to the observed attributes, including those observed attributes which are indicative of dead coral or stressed coral.

One example of a suitable computer program to execute statistical analyses comprises a computer program which calculates the mean, standard deviation and coefficient of variation (CV) for the observed attributes of the coral colony. In reactive monitoring studies, the descriptive statistics may be a characterisation of the health of the selected coral colonies, whereas in randomly selected colonies, the descriptive statistics may be representative of the health of a coral colony population as a whole within the sampling unit. The computer program to execute statistical power analyses may comprise a computer program to calculate regression, ANOVA, chi-square, t-tests, and the like.

The system 30 may also comprise a database of data about the observed attributes of coral colonies recorded at regular intervals over a predetermined period of time, such as for example during the monitoring period. The database may also contain data of observed attributes of coral colonies generated in a period prior to the monitoring period and/or generated in a post-monitoring period. Preferably, the period prior to the monitoring period may be about 12 months to capture seasonal variations in coral health and variation within the population of coral colonies.

System 30 may reside on the hard drive of laptop 26 or be located externally thereof.

Some embodiments of the invention relate to methods of monitoring coral colonies. Figure 2 shows a method 120 in accordance with one embodiment of the present invention. As shown, the method involves the step of selecting a plurality of coral colonies to observe (step 122). Suitable types of coral colonies include, but are not limited to, hard corals, such as massive coral, sub massive or digitate coral, encrusting coral, branched coral, tabulate coral, foliose coral, plate coral, and free-living coral. Coral colonies may also be selected according to taxonomic criteria.

Other benthic classes which may co-exist with coral colonies and be observed in a monitoring study include, but are not limited to, primary producers such as algae, Sargassum sp., and seagrass: Posidonia sp.; sessile invertebrates such as sponge, Ascidians. Gorgonians, soft coral, sea whips, hydroids/anemones, bryozoans, fan worms: and mobile invertebrates such as sea urchins and gastropods. Illustrative examples of algae include, but are not limited to, turf algae, coralline algae, red algae, brown algae and green algae. One or more of these benthic classes may be selected as an observed attribute which is indicative of the health of the coral colonies being monitored.

The number of coral colonies selected for observation may be determined on the basis of obtaining a sample size which is statistically significant and is able to provide sufficient statistical power to detect change in attributes observed in the coral colonies in accordance with statistical techniques well known to those skilled in the art. The term 'statistical power' as used herein refers to the probability that a statistical test will yield statistically significant results and depends on the size of the population sampled and the variability in attributes present within the sampled population.

The plurality of coral colonies may be distributed amongst a plurality of sites, the sites being spaced up to 30km apart. The sites may be selected on the basis of permanent or random site sampling techniques well known to those skilled in the art. Additionally, selection of the sites is determined by a potential impact domain of environmental activities, such as dredging. For example, the potential impact domain may extend up to 40km away from a dredge area in which the dredge footprint extends over 20km offshore. Accordingly, as illustrated in Figure 1 a, each coral colony 32a, 32b, 32c, ... 32n (where n= N number of coral colonies) in the plurality of coral colonies 32 has a unique set of positional coordinates x_a,y_a,z_a, Xb,yt_>,z_b, Xc,yc,z_c, x_n,yn,z_n. Χ,Υ,Ζ (Cartesian) coordinates refers to 3D positioning on orthogonal axes or planes. Usually the 'z' axis is vertical, and the 'x' and y axes horizontal.

The number of coral colonies, their distribution amongst a plurality of sites, the spatial location of the plurality of sites, and the size and shape of a monitored area in which those sites are located may be selected according to a sampling design. The sampling design for a monitoring study (e.g. a longitudinal study) may be based on appropriate statistical models, such as a nested ANOVA model, paired impact and reference sites to obtain desirable degrees of statistical power across the monitored area.

The control system 24 of the base station 14 as described in respect to Figure 1 is used to control and propel the ROV 12 to locate each coral colony 32a, 32b, 32c, ... 32n by coinciding the real-time locational coordinates of the ROV 12 with the unique set of positional coordinates x_a,y_a,z_a, Xb,yb,z_b, Xc,y_c,Zc, Χη,Υη,Ζη of each coral colony 32a, 32b, 32c, ... 32n (step 124). It will be appreciated that the term "coinciding" as used herein does not refer to an exact and precise coincidence of the ROV 12 with the positional coordinates of the coral colonies which would otherwise result in damage or destruction of the coral colony. Rather, the term "coinciding" as used herein refers to location of the ROV 12 in sufficient proximity to the unique set of positional coordinates x_a,y_a,z_a,

Xb,yb,z_b, Xc,yc,z_c, Xn,yn,z_n of the coral colony 32a, 32b, 32c, ... 32n to enable positive identification of the coral colony and for the camera 20 to capture images of sufficient quality and statistical significance for processing by system 30.

The camera 20 may transmit images of the coral colonies 32a, 32b, 32c, ...

32n to the remote located base station 14 (step 126) through umbilical line 16. More than one image of a specific coral colony may be transmitted to the base station 14. Alternatively, the camera 20 may record and store images of the coral colonies 32a, 32b, 32c, ... 32n.

Recorded and/or received images of each colony are then processed to generate data on observed attributes of the coral colonies (step 128) as described above. The steps of controlling the remotely operated underwater vehicle to locate the one or more coral colonies (step 124) and recording and/transmitting images of the one or more coral colonies (step 126) may be repeated at regular intervals over a predetermined period, whereby the images of the one or more coral colonies may be processed to generate data on variation in observed attributes of the coral colonies over the predetermined period.

The predetermined period may be from 3 months to several years, and will typically extend over the period in which a dredging program or some other marine disturbance process is undertaken. The predetermined period may also include a period (e.g. 12 months; extending prior to said dredging program or disturbance process in order to establish baseline variations in observed attributes of the coral colonies associated with coral health. The predetermined period may further include a period post-dating the dredging program or disturbance process to monitor coral colony recovery.

The regular intervals at which steps 124 and steps 126 are repeated may range from three days to 90 days.

The present invention also relates to a system for mapping a boundary of a benthic habitat. The benthic habitat may be located at depths down to about 100m and typically includes naturally occurring and anthropogenic habitats including deep water reefs, shallow water reefs, low profile reefs, high profile reefs; sea grass meadows, kelp forests, sessile invertebrate groups; benthic infauna; and sediment. The boundary of the benthic habitat may comprise a substantially continuous periphery of an area of sea floor demonstrating one or more typical attributes of the benthic habitat of interest.

Referring to Figure 3, where like numerals refer to like features throughout, there is shown a schematic representation of one embodiment of a system 50 for mapping a boundary 52 of a benthic habitat 54. The system 50 includes a remotely operated underwater vehicle (ROV) 12 provided with a camera 20 for transmitting images to a remotely located base station 14 and a means 22 to determine and transmit real-time positional coordinates of the ROV 12 to the remotely located base station 14, such as has already been described with reference to Figures 1 a, 1 b and 2.

It will be appreciated that in this embodiment of the invention, the images transmitted by camera 20 to the remotely located base station 14 comprise images of the boundary 52 of the benthic habitat 54.

The base station 14 is provided with a control system 24, such as has already been described with reference to Figures 1 a, 1 b and 2, to control and propel the ROV 12. In this embodiment of the invention, the ROV 12 is controlled and propelled along the boundary 52 of the benthic habitat 54 by the control system 24 in response to received images of the boundary 52 of the benthic habitat 54. In this way, the ROV 12 may be caused to travel the entire boundary 52 of the benthic habitat 54, while at the same time, the means 22 to determine the real-time positional coordinates of the ROV 12 transmits said real-time positional coordinates of the ROV 12 to the base station 14. Said means 22 may transmit said real-time positional coordinates of the ROV 12 to the base station 14 continuously or intermittently, optionally at regular intervals.

The system 50 also includes a system 56 to process recorded and/or received images of the boundary 52 of the benthic habitat 54 and the real-time positional coordinates of the ROV 12 to generate a representation of the positional coordinates of the boundary 52 of the benthic habitat 54.

The system 56 may comprise one or more computer programs to generate a representation of the positional coordinates of the boundary 52 of the benthic habitat 54, such as the ESRI ARGIS software. In general, the representation of the positional coordinates of the boundary 52 of the benthic habitat 54 may be a graphical representation in the form of a Cartesian or polar map. The system 56 may also comprise a database representation of the positional coordinates of the boundaries 52 of various benthic habitats 54.

System 56 may: reside on the hard drive of laptop 26 or be located externally. The system 50 of the present invention may be employed to facilitate a method of mapping a coordinates of a benthic habitat 54. Figure 4 shows a method 140 in accordance with one embodiment of the invention. As shown, the method 140 involves the step of recording and/or transmitting images of the boundary 52 of the benthic habitat 54 to a remotely located base station 14 with a camera 20 attached to a frame 18 of a ROV 12 (step 142).

The ROV 12 is propelled along the boundary 52 of the benthic habitat 54 in response to the received images of the boundary of the benthic habitat (step 144) by the control system 22.

Real-time positional coordinates of the remotely operated underwater vehicle are transmitted to the remotely located base station as the remotely operated underwater vehicle is propelled along the boundary 52 of the benthic habitat 54 (step 146). Advantageously, the real-time positional coordinates of the ROV 12 substantially coincide with the positional coordinates of the boundary 52 of the benthic habitat 54.

The received images of the boundary 52 of the benthic habitat 54 and the real-time positional coordinates of the remotely operated underwater vehicle 12 are then processed to generate a representation of the positional coordinates of the boundary 52 of the benthic habitat 54 (step 148), In general, the representation of the positional coordinates of the boundary 52 of the benthic habitat 54 may be a graphical representation in the formof a Cartesian or polar map.

It will be readily apparent to a person skilled in the relevant art that the present invention has significant advantages over the prior art including, but not limited to, the following

^■ the system for monitoring coral colonies of the present invention is diverless and therefore the occupational health and safety concerns associated with diver- based monitoring systems are obviated. Further, the system of the present invention can be employed continuously, in particular in poor visibility conditions or adverse weather or sea state conditions in which diver-based monitoring systems would be unable to operate.

^■ The system of the present invention can accurately and precisely relocate coral colonies within the monitoring area by substantially coinciding the .positional coordinates of the ROV with the unique set of positional coordinates of the coral colony and without relying on physical tagging infrastructure which requires installation and maintenance to aid in the relocation of the coral colony and which may damage the coral colony to which it is attached.

■ The system of the present invention is cost-effective in comparison with diver-based monitoring systems and may be employed to monitor a larger sample size (i.e. an increased number of selected coral colonies), thereby improving the statistical power of the system of the present invention in comparison with diver-based monitoring systems.

■ The system for mapping a boundary of a benthic habitat provides real-time mapping capability which is precise and accurate and does not require time-consuming analysis of large amounts of data collected by alternative benthic habitat surveying methods undertaken with multi-beam echo- sounder or side-scan sonar systems.

■ Images recorded and/or transmitted by the camera 20 also provide a means of determining percentage cover of the observed attributes of interest at discrete locations within a sampling frame.

^■ Images recorded and/or transmitted by the ROV 12 can also be used to derive community level metrics including species richness, evenness, health indices and substrate characteristics.

Example: Monitoring Trial

A diver free trial using a known drop camera system and proprietary ROV was conducted at a number of shallow coral reef systems (0.5m - 6.0m) in the Wheatstone Project area west of Onslow in the Pilbara, Western Australia in late 2010.

The drop camera sampled four sites, completing three to five sampling blocks within each site, with between 15 and 25 transects per block and a minimum of six usable images per transect. In all, a total of 267 transects were completed and 1602 images collected. This demonstrates the ability of a drop camera system to efficiently sample in the field, generating a large number of random transects.

The ROV was able to locate the tagged (by means of star pickets) coral colonies and fixed transects in the field. It was also able to position itself over tagged coral colonies to take high quality images despite reduced manoeuvring space due to the star pickets. The ROV system successfully located and collected images for 171 tagged coral colonies at two sites. Two positioning systems on the ROV were trialled:

• USBL - which was found not to be effective at long offsets (>25 m) in shallow water typical of the reef topology at the sites

• GPS surface buoy attached to tether behind the ROV running on AMSA beacon which gave sub-metre accuracy and considered fit-for-purpose for the trial in re-locating tagged coral sites

Field trials demonstrated that diver-free techniques can be used effectively to locate and photograph individual coral colonies and to sample reef sites using random transects. Image quality was found to be comparable to that collected by divers and is sufficient for image analysis for both reactive and long term monitoring. Diver-free techniques can be conducted under challenging conditions where diving would not be permitted for health and safety reasons and are also much more cost efficient. However, to achieve a complete diver free solution the trial identified that a sub metre accurate location system for the ROV would be required to achieve a tagged coral colony sampling design.

The trial concluded that diver-free techniques could (and should) be substituted for divers in coral monitoring studies.

Power to detect change in coral communities sampled using diver-free techniques is equivalent or better than power to detect change in coral communities sampled using divers. Further, diver-free techniques are more cost-efficient and have the potential to mediate many of the health and safety risks associated with conducting diving operations. Power to detect change based on monitoring tagged coral colonies over time is low, indicating more colonies than the 60 established by divers at each of the study sites must be sampled to provide a power of at least 0.8 if this approach is used. Power to detect change based on comparisons of tagged colonies between sites was moderately high but would require a 60% increase above current sampling effort to obtain a power of 0.8. Images for randomly selected coral colonies can be efficiently collected in the field and may provide a viable cost effective alternative to use of tagged coral colonies for monitoring coral health.

The system, apparatus and method of present invention to survey and/or monitor underwater features, particularly reefs and coral colonies, has been developed with the above problems in mind.

Numerous variations and modifications will suggest themselves to persons skilled in the relevant art in addition to those already described, without departing from the basic inventive concepts. All such variations and modifications are to be considered within: the scope of the present invention, the nature of which is to be determined from the foregoing description.

It is to be understood that, although prior art use and publications may be referred to herein, such reference does not constitute an admission that any of these form a part of the common general knowledge in the art in Australia or any other country.

For the purposes of this specification it will be clearly understood that the word "comprising" means "including but not limited to", and that the word "comprises" has a corresponding meaning.

Claims

CLAIMS:

1 . A method of surveying or monitoring an underwater feature, the method including: a) providing a remotely operated underwater vehicle (ROV) with data capture means capable of recording and/or transmitting data to a base station remote from the ROV; b) determining and transmitting real-time positional coordinates of the ROV when underwater to the remotely located base station; c) controlling the ROV to arrive at a desired set of positional coordinates in response to received real time positional coordinates of the ROV; d) capturing data relating to one or more parts of the underwater feature using sensing or detection means associated with the ROV; e) recording and/or transmitting the captured data to the base station.

2. A method as claimed in claim 1 , further including relaying the positional coordinates of the ROV via a tether device extending between the ROV and the base station, the tether device incorporating a series of positional coordinates relay devices.

3. A method as claimed in claim 2, whereby controlling the remotely operated underwater vehicle includes locating one or more of the parts of the underwater feature by comparing the real-time positional coordinates of the ROV and the unique set of positional coordinates of the one or more parts of the feature to be surveyed or monitored.

4. A method as claimed in claim 1 or 2, including surveying or monitoring physico-chemical characteristics of the underwater feature, the method including the steps of; i) the data capture including detecting physico-chemical characteristics in the water using one or more sensors associated with the ROV; ii) transmitting to the base station the positional coordinates of the detected physico-chemical characteristics.

5. A method as claimed in claim 4, including using a number of the positional coordinates to map a physical extent of the physico-chemical characteristics in the water.

6. A method as claimed in any one of the preceding claims, including returning and repositioning the ROV to selected ones of the positional coordinates based on the previously obtained said positional coordinates.

7. A method as claimed in claim 1 , further including processing recorded and/or received data of the underwater feature to generate data relating to detected or observed attributes of the underwater feature.

8. A method as claimed in any one of the preceding claims, including revisiting previously surveyed or monitored parts of the underwater feature to subsequently resurvey or re-monitor at a later time by repeating steps to obtain updated image data of the one or more parts of the underwater feature.

9. A method as claimed in any one of the preceding claims, wherein the underwater feature includes one or more coral colonies, the method including: a) locating the one or more coral colonies from positional coordinates derived via the tether device, b) selecting a plurality of the one or more coral colonies to observe, each said coral colony in the coral colonies having a unique set of positional coordinates; c) controlling the ROV to locate one or more of the coral colonies, by comparing real-time positional coordinates of the ROV with the unique set of positional coordinates of the one or more of the coral colonies, d) recording and/or transmitting images of the one or more coral colonies to the remotely located base station, and e) processing recorded and/or received images of the one or more coral colonies to generate data on observed attributes of the coral colonies.

10. The method according to any one of the preceding claims, whereby controlling the ROV is repeated at subsequent period or periods of time to re- locate the at least one feature and then recording and/or transmitting further images of the at least one feature at periodic intervals of time.

1 1 . The method according to claim 9, wherein the images of the one or more coral colonies recorded and/or received at regular intervals over the predetermined period are processed to generate data on variation in observed attributes of the coral colonies over predetermined said periodic intervals of time.

12. A benthic habitat or underwater feature survey or monitoring system including: a remotely operated underwater vehicle (ROV) having or connected to a geo-referenced position determination means, and a tether connecting the ROV disposed underwater to a surface vessel, the tether including positional coordinate relay means to transmit real time positional coordinates of the ROV underwater to or from an ROV control system on the vessel.

13. A system as claimed in claim 12, wherein the relay means of the tether include multiple positional coordinate determination means whereby each determination means determines its own position in the water.

14. A system as claimed in claim 13,

15. A system as claimed in claim 12, 13 or 14, the ROV including data capture means.

16. A system as claimed in claim 15, the data capture means including at least one camera.

17. A system as claimed in any one of claims 12 to 15, the ROV including physico-chemical detection means capable of sensing/detecting physico-chemical characteristics in the water.