As part of a program aimed at developing a long-duration, subsurface mooring, known as Ultramoor, several modern acoustic current meters were tested. The instruments with which the authors have the most experience are the Aanderaa RCM11 and the Nortek Aquadopp, which measure currents using the Doppler shift of backscattered acoustic signals, and the Falmouth Scientific ACM, which measures changes in travel time of acoustic signals between pairs of transducers. Some results from the Doppler-based Sontek Argonaut and the travel-time-based Nobska MAVS are also reported. This paper concentrates on the fidelity of the speed measurement but also presents some results related to the accuracy of the direction measurement. Two procedures were used to compare the instruments. In one, different instruments were placed close to one another on three different deep-ocean moorings. These tests showed that the RCM11 measures consistently lower speeds than either a vector averaging current meter or a vector measuring current meter, both more traditional instruments with mechanical velocity sensors. The Aquadopp in use at the time, but since updated to address accuracy problems in low scattering environments, was biased high. A second means of testing involved comparing the appropriate velocity component of each instrument with the rate of change of pressure when they were lowered from a ship. Results from this procedure revealed no depth dependence or measurable bias in the RCM11 data, but did show biases in both the Aquadopp and Argonaut Doppler-based instruments that resulted from low signal-to-noise ratios in the clear, low scattering conditions beneath the thermocline. Improvements in the design of the latest Aquadopp have reduced this bias to a level that is not significant.

Long-term field tests of a low-cost acoustic telemetry system were carried out at two sites in Massachusetts Bay. At each site, an acoustic Doppler current profiler mounted on a bottom tripod was fitted with an acoustic modem to transmit data to a surface buoy; electronics mounted on the buoy relayed these data to shore via radio modem. The mooring at one site (24 m water depth) was custom-designed for the telemetry application, with a custom designed small buoy, a flexible electro-mechanical buoy to mooring joint using a molded chain connection to the buoy, quick-release electro-mechanical couplings, and dual hydrophones suspended 7 m above the bottom. The surface buoy at the second site (33 m water depth) was a U.S. Coast Guard (USCG) channel buoy fitted with telemetry electronics and clamps to hold the hydrophones. The telemetry was tested in several configurations for a period of about four years. The custom-designed buoy and mooring provided nearly error-free data transmission through the acoustic link under a variety of oceanographic conditions for 261 days at the 24 m site. The electro mechanical joint, cables and couplings required minimal servicing and were very reliable, lasting 862 days deployed before needing repairs. The acoustic communication results from the USCG buoy were poor, apparently due to the hard cobble bottom, noise from the all-steel buoy, and failure of the hydrophone assembly. Access to the USCG buoy at sea required ideal weather

We consider an alternative to traditional high-modulus synthetic electro-optical-mechanical (EOM) mooring cables that are being used in single-point moorings for deep-ocean observatories. The alternative cable design is based on using low-modulus nylon or polyester fibers as the strength member. High-modulus EOM cables such as those that use Vectran fibers as the strength member are usually constructed with the conductors and optical fibers in the core and the strength member on the outside. The key aspect of the new design is that the strength member is placed in the center of the cable and the conductors and fibers are wrapped around the outside at a high helix angle to accommodate stretching of the center-strength-member. A comparison of the static and dynamic responses of moorings constructed with nylon, polyester, and Vectran EOM cables (for mooring scopes of 1.1 and 1.2 and deployment depths of 1800, 3000, and 5000 m) shows that the maximum total tensions of moorings made with nylon EOM cables are lowest under all conditions. Differences between the nylon and the Vectran EOM cable moorings are due principally to the differences in the dynamic tensions. Differences between the nylon and the polyester EOM cable moorings are due mainly to differences in static tensions caused by the higher specific gravity of polyester fibers. Reduction in the scope of all the moorings from 1.2 to 1.1 resulted in significantly higher tensions for the polyester and Vectran EOM cable moorings but only slightly higher tensions for the nylon EOM cable moorings.

A buoy-based observatory that uses acoustic communication to retrieve data from water column and seafloor instruments has been developed and deployed in 2362 m of water offshore Vancouver Island. The system uses high-rate (5000 bps) acoustic modems that are power-efficient (on order 1000 bits per joule) to telemeter data from an ocean bottom seismometer and a sensor monitoring a cold seep site near the Nootka fault. The buoy includes a Linux-based embedded controller, the modem base station and meteorological sensors. Data is off-loaded from the buoy using ftp, and remote login capability allows the acoustic communication schedule to be modified when instruments are added or removed from the network. The system has been operational for one year, typically transferring more than 500 Kbytes of data per day from two seafloor instruments.

Anew oceanographic mooring system, Ultramoor, has been developed to reduce the cost and effort associated with making sustained observations in remote parts of the oceans. 1 Present mooring technology, which requires annual or at best, biennial maintenance, employs internal recording instruments and does not meet the need for timely, cost-effective data. Ultramoor is designed for unattended deployments of five years or more and provides regular data updates from instruments positioned throughout the water column. It eliminates the requirement for frequently scheduled maintenance, which is an important factor in the total cost of long-term monitoring programs. While the initial Ultramoor has been instrumented with current and temperature sensors, the design is compatible with a variety of low-power instruments with digital data output. We envision the new system as a prototype for a new generation of …

Mooring systems that deliver power and data communication to sub-sea instrumentation figure prominently in future plans to build ocean observatories. Currently, this technology is immature and technological advancements need to be made before such systems are ready to be routinely implemented. This paper describes the current state of the art in mooring systems appropriate to the deepwater ocean observatory context and outlines the technological challenges that need to be addressed in order to realize moored ocean observatories as envisioned for the next generation of ocean observing systems.

A moored-buoy system for collecting real-time seismic data from the coastal ocean has been developed and will be deployed for its initial field trial in the fall of 2003. The key component in this moored system is an ultra-stretchy mooring hose that provides compliance for waves and currents and protects the electrical conductors connecting an ocean bottom seismometer (OBS) to a surface buoy from the effects of bending and stretching. This hose is able to stretch to more than twice its unstretched length of 30 m without putting excessive strain on the electrical conductors embedded in its wall. In the initial trials of this system, the OBS will be deployed on the bottom in 40 m of water and connected to the mooring hose through a cable on the seafloor. It will transmit continuous data at a rate of about 5000 bps to a radio link in the surface buoy. A repeater modem located at the Gay Head lighthouse on Martha's Vineyard about 18 km from the mooring site will receive the transmissions and forward the data to our laboratory at WHOI, about 46 km distant. A GPS receiver on the surface buoy will be configured to send accurate and synchronized time to the OBS on the seafloor, which will make it possible to include data from these undersea systems in the existing seismic data network without the need for any pre-processing. Power to operate the RF link and the OBS will be supplied by solar panels and rechargeable batteries on the surface buoy.

Buoy-based moored observatories require a reliable strength member and conductor linkage between sea floor instrumentation and surface platforms. Both electrical conductors and optical light-guides can only survive if they are strained within their low elastic elongation limit, and if in addition the cable design avoids excessive curvature and point pressure of the optical fibers. All lightweight cables with textile strength members have working elongations in excess of the conductor stretch limits. Cable-like lightweight mooring members with considerable stretch are presented which maintain a "comfort zone" for their conductors. These design include lightweight electro-mechanical (EM) and electro-optical mechanical (EOM) mooring cables, and textile tire cord reinforced rubber stretch hoses with integral electrical and optical conductors. Finally, recent experience with an EOM cable as part of an ocean observatory mooring, deployed offshore California, is discussed in terms of its reliability under serve storm conditions.

As possible replacements for our venerable VACMs and VMCMs, we have been testing a number of modern current meters which are based on sound propagation principles, either travel time differences between transducers or Doppler frequency shift due to scattering from suspended particles. Comparisons with our traditional instruments, which have mechanical sensors, have produced more questions than answers and after four different experiments in the deep ocean near Bermuda, we are not yet able to provide definitive conclusions.

A new moored measurement system (ULTRAMOOR) has been developed whose aim is to reduce the cost and effort associated with making sustained in situ observations, especially in remote parts of the oceans. Present mooring technology, which typically requires annual, or at best biennial, maintenance and employs internally recording instruments, does not meet existing or future needs for timely, cost-effective data. ULTRAMOOR is designed for unattended deployments of five years or more with regular data updates from instruments positioned throughout the water column. It eliminates the requirement for frequently scheduled maintenance, which is an important factor in the total cost of long-term monitoring programs. While the initial ULTRAMOOR has been instrumented with current and temperature sensors, the design is compatible with a variety of low power instruments with digital data output. We envision the system as a prototype for a new generation of potentially expendable mooring types whose instruments spend almost all of their working lives at sea. ULTRAMOOR is a subsurface mooring equipped with a combination of modern acoustic current meters and current profilers. Each instrument transfers its data to an acoustic modem, which forwards these data to a central receiver. The central receiver then loads the data into an array of expendable data capsules, which release themselves at scheduled intervals throughout the deployment period and float to the surface. Once on the surface, they transmit their stored data via small satellite transmitters. The prototype ULTRAMOOR has been deployed successfully on two occasions. The long-term test mooring is instrumented with six acoustic current meters. Three of the ten data capsules have surfaced since the deployment and have provided high quality data from five of the six current meters. Remaining data capsules are scheduled to release at six-month intervals until November 2004. Preliminary results indicate that the acoustic links are working flawlessly, that eight of the ten data capsules are functioning normally, and that the data in the capsules are true representations of the data collected by the individual instruments.

A data delivery system was developed for the Northern Gulf of Mexico Littoral Initiative that allows access to data from bottom mounted instrumentation. The system consists of two parts, a trawl resistant sub-surface component and a separate surface buoy. The sub-surface component employs a Trawl Resistant Bottom Mount containing an Acoustic Doppler Current Profiler equipped with a Micro-Modem (muModem.) The surface expression consists of a buoy equipped with an acoustic receiver (Utility Acoustic Modem, or UAM), a system controller and an Argos transmitter (PTT.) The muModem acoustically telemeters data from the ADCP on an hourly schedule to the UAM on the nearby (similar to500m) surface buoy. Data from the acoustic receiver is forwarded via the controller to the Argos transmitter. To maximize data throughput of the Argos link the controller loads a circular buffer containing the most recent eight hours of data into the PTT each hour. This data is continuously transmitted until the next hourly update. The controller also performs resynchronization of the acoustic system in the event acoustic communications are lost. One particular benefit of this system is the ability to perform measurements in high traffic locations while maintaining the surface buoy at a safe distance from navigation aids. One system is currently deployed in a high traffic area, in Horn Island Pass, due south of Pascagoula, MS. This paper describes the overall system and presents data from initial deployments.

A clockwise circulation around Georges Bank was measured by means of moored current meters, aircraft-tracked surface drifters, and satellite-tracked drifters drogued at 10 m. The strongest flow was in a narrow jetlike current (30 cm s−1) along the northern flank of the bank. The flow of shelf water on the southern flank was westward (10 cm s−1) toward the Middle Atlantic Bight; some of this water flowed northward through the eastern side of Great South Channel and recirculated around Georges Bank. The satellite-tracked drifters and the moored observations indicate that the circulation around the bank was not completely closed and considerable variability occurs in the trajectory of an individual water particle.