Mooring Matters: Sustained Measurements of Crucial Ocean Currents

Mooring Matters: Sustained Measurements of Crucial Ocean Currents

For the next installment in our series of technical articles, Dr. Peter Spain of Teledyne RD Instruments discusses the development of ADCP technology and the use of syntactic foam buoyancy in subsea moorings for sustained measurements of ocean currents.

Sustained Measurements of Crucial Ocean Currents

Teledyne RDI ADCPs and DeepWater Buoyancy Deliver a Go-To Combo

By Peter Spain Ph.D., Teledyne RD Instruments

Current Profiling

ADCPs are sonar systems that measure motion underwater. Using sound waves, they work like hand-held radars used by police to catch speeding motorists. To measure motion, ADCPs emit sound bursts along beams angled upward or downward.

Echoes are returned due to scattering off particles. Because zooplankton and suspended sediments are carried by the moving water, echoes scattered off them carry a change in pitch; this is the Doppler Effect. It tells how fast the current is moving and in what direction.

Sound waves propagate through the water column so echoes are returned and processed from many depths. The vertical range of this collection of measurements—called a profile of ocean current velocities—is greater for lower frequency sound waves.

Introduction

Next to the eastern seaboard of continents stream the largest currents on the planet. They have been well-known to seafarers for centuries. Found around the globe, these major ocean currents are energetic, narrow and deep. They exist in all ocean basins, north and south of the equator: Gulf Stream, Kuroshio, and Brazil, Agulhas, East Australian Currents respectively.

These strong currents move much warm water poleward from low latitudes; thus, they redistribute heat for the earth’s climate system. On shorter time scales, they affect regional and local weather. These flows transfer organisms, nutrients, chemicals, debris, and pollutants – all affect life in and out of the sea and along coastlines. And strong currents affect routes selected by shipping.

Crucial ocean currents have been studied to measure their structure, transport, and fluxes—and, in recent times, their changes on seasonal and longer times scales. In ball-park numbers, these flows span 100 km, move faster than 100 cm/s, and carry 100 times the outflow of the world’s largest river.

Measuring these currents has been challenging. To capture their extent, measurements need to reach deep. To resolve changes over time, measurements need to be sustained. And to survive, persistent measurement methods need to withstand the energy of these powerful currents. For example, surface drifters, floats, and gliders are quickly swept away in strong upper-ocean currents.

Figure 1. Large ADCP Buoys with Teledyne RDI ADCPs off South Africa. Credit: SAEON Egagasini Node. http://asca.dirisa.org/

Programs making long-term measurements of important currents rely on resilient moorings. And for measuring strong currents in the upper ocean, these moorings carry ADCPs.

In this two-part report, we first review some background to moorings carrying Teledyne RDI ADCPs mounted in DeepWater Buoyancy buoys. Then we look at sustained measurements of crucial ocean currents in some less-familiar places.

Figure 2. William Richardson, pioneer of Buoy Group at WHOI. Credit: Nova Southeastern University. LINK

Background

Almost 60 years ago at WHOI [1], William. S. Richardson launched the modern era of ocean-current metering. For studying deep-sea currents—notably, the Gulf Stream—he identified and invented two essential tools: a recording current meter and an unattended mooring. Richardson’s intent for the mooring was to suspend current meters at several depths. The meters would record long time-series of currents simultaneously. For studying currents across large areas, Richardson deployed several moorings.

Over the next two decades, the Buoy Group at WHOI engineered this reality. Their impressive results were hard won in the harsh and unforgiving environment of the deep sea. You can read more at this link: 50-years-of-the-whoi-buoy-group. For the UK story, see this PDF: UK_moorings.pdf.

Along the way, one key problem was mooring loss. A leading culprit was large drag force caused by strong currents. The adjacent graphic shows a section of the Gulf Stream in the upper 2000 m. Speeds are directed along-stream. Notice the extreme current speeds in the upper ocean and the large spatial gradients.

[1] Woods Hole Oceanographic Institution. See Richardson et al. report (WHOI Ref: 63-1)

Figure 3. Gulf Stream currents and thermal structure. Distance: km, Current speeds: cm/s. Credit: Halkin + Rossby, 1985. LINK

For recording currents accurately, the meters need to hold position in three dimensions. The mooring must therefore be taut. To this end, sizable buoyancy is added to the mooring line. Yet, unavoidably, these elements increase drag forces exerted by strong currents.

Besides sweeping away moorings, strong drag forces caused mooring lines to pull apart (part way up) or to blow-over. The latter mooring motion carried instruments and mooring elements in large vertical excursions: 300-500 m in a tall mooring. See Fig. 4. These excursions confounded interpretation of measurements. Worse, the mooring could sink when in-line buoyancy was crushed by high pressure at unplanned depths.

Figure 4. Large vertical excursions of a mooring line in the Gulf Stream. Time series of two pressure sensors mounted in-line and separated by 200 m.  Credit: Hogg, 1986.  LINK

Mooring Changes

By the mid 1980’s, the design of both moorings and current meters had evolved substantially. Fig. 5 shows typical designs. Highlighted are important changes in mooring components. Notice the change in where buoyancy is added.

One strategy to decrease mooring losses was reducing drag. Major currents have strong near-surface speeds. To avoid these, moorings that terminated subsurface were developed. Many were topped with large spherical buoys. They provide the same buoyancy for less drag than smaller options. To solve the crushing problem during severe blow-over, these large spheres were made of syntactic foam.

Figure 5. Deep-sea moorings—pre ADCPs: Changes from early-1960’s to mid-1980’s. Credit: Richardson et al., 1963 WHOI Ref 63-1;  Molinari, 1986 LINK

Beginning with Hogg (1986), scientists introduced methods for correcting measurements confounded by blow-over of a mooring. As well, methods for evaluating the design and dynamics of moorings were more available. See Mooring Design and Dynamics

Figure 6. Spherical syntactic foam buoys housing Teledyne RDI ADCPs. Credit: NOAA. LINK

ADCPs

From the mid 1980’s, ADCPs provided a new solution for measuring strong surface currents. A mechanical current meter must be immersed in the flow it measures. In contrast, ADCPs are sonar systems; they can measure current velocity remotely. They emit an acoustic signal and then process the informational content of returning echoes.

Scientists realized that ADCPs looking upward could be used to measure strong surface currents while deployed in slower waters below. This helped reduce drag on the mooring. To this end, ADCPs were mounted in the flotation buoy atop subsurface moorings. Pioneering this approach was Friedrich A. Schott at University of Miami.

DeepWater Buoyancy’s antecedent, Flotation Technologies, developed these buoys as standard kit for ADCPs. Using syntactic foam for flotation elements permitted custom designs. Notably, a cylindrical instrument well was inserted along the vertical axis of the large spheres. Housing ADCPs in this sheltered location reduced current drag on the mooring. Since the late 1980’s, ADCPs have been commonly mounted atop a subsurface mooring within a collar of syntactic foam.

To further decrease drag on the mooring, new designs evolved for syntactic flotation buoys. An elliptical-shaped float that is more hydrodynamic became a common component on many deep sea moorings.

Figure 7. DeepWater Buoyancy Elliptical ADCP Buoy.  LINK

For measuring very strong currents, such as tidal streams, a torpedo-shaped buoy is now state-of-the-art. This approach reduces drag and increases stability in pursuit of moored nirvana—low tilt and minimal vertical excursions.

Figure 8. DeepWater Buoyancy StableMoor® Buoy holding Teledyne RDI ADCP. Credit: Bedford Institute of Oceanography. LINK

Moored ADCP Arrays

A mix of methods is needed to clarify the long-term effects of global warming. Moored arrays in major ocean currents provide an essential ingredient. Insights have come from researchers using computer models and satellite-based observations. And drifters, gliders, and floats can provide snapshots. Yet there is no substitute for hanging around in these deep and energetic flows.

For scientists to see long-term trends and large-scale connections, moored arrays must collect sustained time series. And for collecting this information Teledyne RDI ADCPs mounted in DeepWater Buoyancy flotation provide a go-to combination.

.   .   .   .   .   .   .  

 

In Part 2 of this report, we review some compelling examples of moored ADCP arrays measuring crucial ocean currents around the globe.

About DeepWater Buoyancy, Inc.

DeepWater Buoyancy creates subsea buoyancy products for leading companies in the oceanographic, seismic, survey, military and offshore oil & gas markets.   Customers have relied on our products for over thirty-five years, from the ocean surface to depths exceeding six thousand meters.

Learn more at www.DeepWaterBuoyancy.com

About Teledyne RD Instruments

With well over 30,000 Doppler products delivered worldwide, Teledyne RD Instruments is the industry’s leading manufacturer of Acoustic Doppler Current Profilers (ADCPs) for current profiling and wave measurement applications; and Doppler Velocity Logs (DVLs) for precision underwater navigation applications. Teledyne RDI also supplies Citadel CTD sensors for a variety of oceanographic applications.

Learn more at www.teledynemarine.com/rdi/

2018 European Teledyne Marine Users Conference

2018 European Teledyne Marine Users Conference

Sponsors and Exhibitors

DeepWater Buoyancy is co-sponsoring and exhibiting at the first European Teledyne Marine Users Conference .  The event is being held in Cannes France, October 9-11.

We will be represented at the event by Dan Cote, our Sales Manager.  If attending, please be sure to stop by our exhibit table and visit with him.

 

About the Event

TMTW offers a packed, non-stop schedule that truly offers something for every level of users, from novice to seasoned pro.​

Morning sessions will be comprised of three concurrent tracks dedicated to presentations given by Teledyne users from around the globe, who will share their experiences, challenges and solutions using Teledyne products in a wide array of application areas, including:

  • Oceanographic Research
  • Hydrography
  • Offshore Energy
  • Civil Engineering / Infrastructure
  • River/Stream Monitoring
  • Security / Defense
  • Aquaculture / Fisheries​

Attendees are sure to learn new and helpful information from these sessions, not only from the speakers, but from the questions and answer, and interaction with their industry peers in these sessions.

Afternoon sessions are comprised of Teledyne Marine product / software training, new product and application introductions, Q&As with Teledyne’s technical teams, dockside and on-water demonstrations, one-on-one meetings, and an opportunity to visit with our top-tier co-spons​​ors to discuss their third party solutions and services.

Questions?  Please contact Margo Newcombe at margo.newcombe@teledyne.com.​

For more details about the conference: ClickHere

To register: ClickHere

About DeepWater Buoyancy, Inc.

DeepWater Buoyancy creates subsea buoyancy products for leading companies in the oceanographic, seismic, survey, military and offshore oil & gas markets.   Customers have relied on our products for over thirty-five years, from the ocean surface to depths exceeding six thousand meters.

Learn more at www.DeepWaterBuoyancy.com

About Teledyne Marine

Beginning as a small collection of unique marine solution providers and expanding to a powerhouse of highly engineered, high performance solutions for a broad range of markets, Teledyne Marine now offers the largest breadth of marine technology in the industry.

With technologies divided into 5 core segments; Imaging, Instruments, Interconnect, Seismic and Vehicles, Teledyne Marine sales staff can address not only brand level solutions, but turn-key, customized systems that leverage our full range of technology. Our goal is to provide one-stop purchasing capability, world-wide customer support, and the technical expertise to solve your toughest challenges.

A Sea of Solutions…..One Supplier.

Learn more at teledynemarine.com

NEW Pop-Up Buoy for EdgeTech PORT LF-SD.

NEW Pop-Up Buoy for EdgeTech PORT LF-SD.

Announcement

DeepWater Buoyancy, Inc. announces that it has developed a new Pop-Up Buoy Recovery System (PUB) for the EdgeTech PORT LF SD Acoustic Release.  Like the original product, the new PUB allows for direct retrieval of seabed packages, such as anchors, anchor lines, and bottom-mounted frames and instruments.

The new product was developed with EdgeTech’s product development team at the request of Woods Hole Oceanographic Institute.

Pop-Up Buoy Product Details

Easily mounted to any framework, the assembly sits on the seafloor until the acoustic release is activated. Once the release completes its disconnection, the buoy lifts free from the canister and rises to the surface. A synthetic line connects the buoy directly to the framework of the seabed item and allows for retrieval.

The buoy is outfitted with an electropolished 316 stainless steel frame.  The canister holds 75 meters of 1/4″ synthetic line. (Other line lengths are available upon request.) The recovery buoy is made from high-strength DeepTec® solid syntactic foam. The foam is finished with an abrasion-resistant, polyurethane elastomer coating.

The canister is made from PVC and 316SS plate. It has a rugged design and has attachment features to permit various mounting configurations, including easy mounting to our BTM-AL50 tripod bottom mounts.

To learn more about the PUB – CLICK HERE

Acoustic Release Product Details

The PORT Push Off Release Transponder is ideal for deployments in coastal environments. The mechanical drive off system is the best choice for deployments where acoustic release mechanisms can experience growth or sediment build up. Its unique push-off mechanism provides reliable release every time.

The low frequency acoustic command structure is proven to be very reliable and is unsurpassed in multi-path environments.

Features:

  • All Aluminum components
  • Simple and easy maintenance
  • Small lightweight package
  • Medium load acoustic release
  • Full transponder capability
  • 1.25 years on alkaline batteries
  • Reliable and secure command coding
  • including Enable, Disable and Release commands
  • Purge Port
  • Auto Disable
  • Tilt & Release indication

To learn more about the PORT LF SD – CLICK HERE

About DeepWater Buoyancy, Inc.

DeepWater Buoyancy creates subsea buoyancy products for leading companies in the oceanographic, seismic, survey, military and offshore oil & gas markets.   Customers have relied on our products for over thirty-five years, from the ocean surface to depths exceeding six thousand meters.

Learn more at www.DeepWaterBuoyancy.com

About EdgeTech

EdgeTech is a leading manufacturer of underwater technology solutions. The company is known worldwide for its high quality products which include: side scan sonars, sub-bottom profilers, bathymetry systems, AUV and ROV-based sonar systems, combined and customized solutions. In addition to the full line of underwater survey products, EdgeTech provides reliable USBL systems, transponder beacons, deep sea acoustic releases, shallow water and long life acoustic releases, MRUs and customized underwater acoustic command and control systems.

Learn more at www.edgetech.com

DeepWater Buoyancy in 2018 MTR100

DeepWater Buoyancy in 2018 MTR100

Announcement

DeepWater Buoyancy has again been selected for the prestigious Marine Technology Reporter “MTR100”.

Marine Technology Reporter (MTR) magazine is the world’s largest audited circulation publication serving the global Marine Technology Market. This month, MTR released its 13th Annual Listing of 100 Leading Subsea Companies.

DeepWater Buoyancy is proud to be amongst a distinguished collection of companies that include: Teledyne Marine, Kongsberg, Hydroid, and Sonardyne International, to name just a few.  In addition to being selected, a short article about DeepWater Buoyancy was included in the publication.

MTR100 Article

DeepWater Buoyancy is the world’s largest supplier of subsea buoyancy to the ocean science community. The product line is more than 35 years old and is known throughout the world and in all offshore marine markets. DeepWater Buoyancy also has a vast and growing product line of buoyancy solutions for offshore oil and gas and technology companies. Though it offers products for shallow water applications, it specializes in deepwater, providing solutions to depths of 6,000 meters and beyond.

In 2013, DeepWater Buoyancy acquired the rights and designs for the legacy Flotec material technology and products, and has been producing, improving and growing the Flotec product line. Each year the product line improves and new items are added in response to market conditions, changing technology, and customer requirements. In addition to product innovation, new processes and equipment are added to the companies already wide capabilities.

At the heart of the DeepWater Buoyancy product line are the subsurface ADCP buoys, originally developed for Teledyne RD Instruments’ ADCPs. Consisting primarily of both spherical and elliptical buoys, the product line also includes the unique StableMoor® Mooring Buoys. These torpedo-shaped buoys are engineered to house ADCPs and other sensors for high current data collection applications. By design, the StableMoor® reduces drag and increases mooring stability in extreme fl ow regimes, thereby producing superior data sets.

However, DeepWater Buoyancy’s product line goes well beyond ADCP buoys. In the oceanographic market there are bottom mounts, instrument collars, and cable floats. For offshore oil and gas, there are installation blocks, modular buoys, deepwater marker floats and ROV buoyancy. In addition to DeepTec® syntactic foam products and custom-engineered components, there are also plastic, composite, polyurethane and fabricated metal products.

DeepWater Buoyancy StableMoor® Mooring Buoy outfitted with a trim bar and carbon fiber instrument wings.

 

About DeepWater Buoyancy, Inc.

DeepWater Buoyancy creates subsea buoyancy products for leading companies in the oceanographic, seismic, survey, military and offshore oil & gas markets.   Customers have relied on our products for over thirty-five years, from the ocean surface to depths exceeding six thousand meters.

Learn more at www.DeepWaterBuoyancy.com

About Marine Technology Reporter

Marine Technology Reporter magazine is the world’s largest audited circulation publication serving the global Marine Technology Market. From offshore energy to subsea defense to science and technology, MTR covers it all.

Each issue is packed with the latest cutting edge technology from the industry’s leading companies, as well as exclusive insights and market analysis that are critical in today’s subsea industry.

If it is subsea industry related technology you seek, you will find it in Marine Technology Reporter Magazine.

Learn more at www.marinetechnologynews.com

Exhibiting at Oceans in Action

Exhibiting at Oceans in Action

Sponsors and Exhibitors

DeepWater Buoyancy is co-sponsoring and exhibiting at the Marine Technology Society’s 8th annual Oceans in Action workshop.  The event is being held in Gulfport Mississippi on August 21st and 22nd.

We will be represented at the event by Chris Kelly and Kurt Fromhertz, our sales representatives in the gulf coast.  If attending, please be sure to stop by our exhibit table and visit with them.

 

About the Event

The Oceans In Action Workshop is an annual event featuring new technologies in the maritime industry.  Day one consists of updates from federal, state, and regional organizations and new technologies that have helped their missions over the past year.  New technologies of interest to local agencies are also presented. Day two is our industry-focused day and has historically consisted of panels on current and emerging topics.  This year, resulting from a closer collaboration with the Commander, Naval Meteorology and Oceanography Command, our event is even more exciting!

Day two will begin with pier-side demonstrations of select technologies associated with the Advanced Navy Technology Exercise (ANTX). Workshop participants will be shuttled to the Port of Gulfport to watch staged demonstrations of new technologies, review results of exercises recently held in the Gulf of Mexico, and to tour recently-completed facilities, including the new University of Southern Mississippi (USM) Marine Research Center.  Participants will be shuttled back for luncheon presentations, a panel on the Blue Economy, and Business-to-Business/Business-to-Government meetings.

Highlights

  • Keynote Addresses by leading State and Navy Officials
  • Tours of the new USM Marine Research Center
  • Pierside demonstrations associated with the Advanced Naval Technology Exercise (ANTX): Gulf Coast
  • Blue Economy Panels: BlueTech Clusters and Finding Seed/Venture Capital
  • B2B/B2G meetings with federal agency representatives and large prime contractors

Speakers from the following agencies:

  • Commander, Naval Meteorology and Oceanography Command (CNMOC)
  • Naval Research Laboratory – Stennis Detachment (NRL)
  • NOAA’s National Data Buoy Center (NDBC)
  • NOAA’s National Centers for Environmental Information (NCEI)
  • USGS Hydrologic Instrumentation Facility (HIF)
  • USM’s School of Ocean Science & Technology/USM’s Marine
    Research Center
  • The U.S. Integrated Ocean Observing System (IOOS)

For additional information contact Laurie Jugan at laurie.jugan@usm.edu

To register: ClickHere

About DeepWater Buoyancy, Inc.

DeepWater Buoyancy creates subsea buoyancy products for leading companies in the oceanographic, seismic, survey, military and offshore oil & gas markets.   Customers have relied on our products for over thirty-five years, from the ocean surface to depths exceeding six thousand meters.

Learn more at www.DeepWaterBuoyancy.com

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