Ocean Networks Canada - adcp

Ocean Properties

dwowens@uvic.ca — Thu, 26 Sep 2013 22:20:41 +0000

Oceanographers and marine scientists measure or observe attributes or properties of the ocean that allow them to interpret water or component or organism behaviour. Although Ocean Networks Canada cannot measure all required parameters, many instruments are available to provide useful data.

This section discusses the properties measured and provides links to the instruments that provide all or part of the information. Not all parameters are measured at all locations, and some locations have more than one instrument that will measure the same feature in different ways.

Bottom Animal Behaviour

Sometimes biologists have to see animals to understand their actions related to abundance, feeding, competition, and mating. Thus, a camera on the seafloor can often reveal phenomena that are not possible to measure with other means. With high-resolution lenses, the camera can see animals down to 1 mm in size on the seafloor. With a pan and tilt control, the camera can look up into the water column to assess fish and zooplankton. Visual cameras need light that is otherwise absent at most of our site depths. To minimize light pollution, which is unnatural to the deep-ocean environment, we limit lights-on time, scheduling it to descrete time blocks.

Conductivity

Unlike fresh water, saltwater contains free ions and can conduct electricity. We can use the conductivity as a means to calculate the salinity. Salinity is subsequently used, along with Temperature and Pressure, to calculate density. For a given temperature and pressure, fresher seawater is lighter (less dense) and saltier seawater is more dense. Salinity is also very important to marine organisms whose ability to regulate body salts can be limited. ‘Average’ seawater salinity for surface coastal oceans is about 32 parts per thousand. Conductivity is the C in the CTD instrument. The units of measure for Conductivity are Seamans per metre [S/m].

Currents

Tidal currents are a dominate factor influencing water behaviour along the BC coast, while winds and topography can also influence local flow characteristics. Changes in flow rates and directions are vital in determining exchange rates of water properties and habitat conditions. Advanced computer models can be used to predict flow patterns into the future, or during unusual circumstances (e.g., pollutant release from a sunken vessel).

Today, oceanographers use Acoustic Doppler Current Profilers (ADCP) to look at flow patterns through the entire water column. This bottom-mounted instrument looks upward and uses weak high-frequency acoustic signals that bounce off particles to determine the flow rates in layers throughout the water column.

Density

A key measure in oceanography is the seawater density. Adding heat makes the water lighter (less dense), adding salt make it heavier (more dense). Conversely, colder water is heavier and fresher water is lighter. Combinations in between can have various densities. Seawater is also very slightly compressible, and at large ocean depths (i.e. >1000 m) seawater is slightly compressed to higher densities. Denser seawater always sinks underneath lighter seawater, so that at any one location, the lightest seawater is at the surface and the densest is at the bottom. Density is measured in units of kilograms per cubic metre, or kg/m³. Typical values in the ocean range between 1024-1030 kg/m³. Often the pressure contribution is small and we are interested in local changes that might only show up in the first few decimal places, so a quantity called sigma-t is considered that is the seawater density calculated from the in situ temperature and salinity, but at zero (atmospheric) pressure, minus 1000. Therefore sigma-t values range between 23 and 28 kg/m³.

Depth

Why measure depth when the instrument never moves from one place on the bottom? The pressure sensor measures the water column height as tides go up and down. Although tidal height predictions are very useful, weather and wind conditions can also affect the real height of the water level. Tidal height can influence water movement and bottom currents. Also, pressure near the bottom of the ocean can vary as the density of the overlying water above varies. Colder and saltier seawater is more dense than warmer and fresher seawater, and will result in a higher pressure for the same water depth.

The pressure sensor is part of the CTD instrument (the D, for depth, in CTD). The average depth of the ocean is 3750 m; the deepest Ocean Networks Canada instrument is 2660 m in the Cascadia Basin.

Left: A September oxygen profile of Saanich dissolved oxygen. Levels are very low below 70 m and near anoxic below 120 m. Courtesy I. Beveridge. Right: A ship-based cast in the Strait near the Fraser Ridge shows dissolved oxygen (the purple line) and water clarity with depth (the pink line). The slightly lower clarity near the surface is caused by the Fraser River sediments. At the bottom, however, currents are resuspending bottom sediments and water clarity is much lower.

Salinity

What distinguishes the ocean from all other water bodies on Earth is that it is salty. When salts are added to water, the dissolved ions actually allow the water molecules to compact more closely together, thus increasing the water density. The dissolved compounds in seawater are remarkably well mixed over the entire globe, and have been present since the ocean was formed some 4 billion years ago. The dissolved minerals in seawater cover, although sometimes in minute quantities, nearly all the elements of the periodic table. The key ingredients include Chlorine ions (55% by weight), Sodium ions (30.6% by weight), and Sulphate ions (7.7% by weight), representing already 93% of the dissolved compounds in seawater by weight. The Salinity of water is measured by the total weight in grams of dissolved compounds per kilogram of seawater, which translates to about 35 gm/kg, or 35 parts per thousand. Rather than measure the actual dissolved elements, we now measure the conductivity, temperature, and pressure using electronic sensors, and using standard formulae, calculate the salinity assuming a “standard” oceanic composition. Like temperature (heat), changes in the salt concentration only occur near the ocean surface. Rain or river run-off adds fresh water, which dilutes the salinity, whereas in hot regions, evaporation takes fresh water away into the atmosphere in the form of water vapour, thus increasing the salt concentration. The modern units for Salinity are “practical salinity units” [psu], which are equivalent to the number of grams of dissolved compounds per kilogram of water.

Temperature

The two most important properties that help oceanographers understand the physical structure of the water column are temperature and salinity. Along with pressure, they determine the density of seawater. For a given salinity and pressure, warmer seawater is lighter, whereas colder seawater is more dense. Denser seawater always sinks beneath lighter seawater, thus density differences alone can cause water to move. Heat content also influences many organisms – often triggering phytoplankton to grow faster and animals to reproduce. Except for conditions near volcanic activity, changes in water temperature occur at the ocean surface. In the summer, surface water is heated, while in the winter, surface water is cooled. Away from the surfact, changes in water temperature are caused by mixing volumes of water with differing temperatures. The CTD instrument also measures temperature (the T in CTD). Surface waters in British Columbia range from 6 to 20ºC. The unit of measure for Temperature is degrees Celsius [ºC].

Water Clarity

Coastal waters can be very cloudy. The clarity gives oceanographers an idea of the suspended particulate level in the water. Many things can cause high particulate load, but river runoff and plankton blooms are the major sources. Ocean Networks Canada measures the particulate load with a Transmissometer that shoots a narrow beam of light through about 20 cm of water to a receptor; particles will bounce the light away from the receptor, yielding a lower transmission level. Because the Ocean Networks Canada transmissometer is on the ocean floor, we will also see the resuspension of sediments from the bottom.

Zooplankton Behaviour

The tiny animals that eat phytoplankton are a vital source of food for most larger animals in the ocean, including fish and corals. ‘Zooplankton’ is a term that includes a wide variety of species, ranging from tiny copepods to krill to jellyfish. Ocean Networks Canada uses acoustic methods to detect zooplankton with the Zooplankton Acoustic Profiler (ZAP). Very low strength, high-frequency (200 kHz) acoustic pulses from the bottom are directed upward and bounce off zooplankton in the water. To access food, most zooplankton migrate to the photic zone near the surface to feed on phytoplankton. But during the day, zooplankton can be detected by visual predators such as fish, so they hide at depth while the sun is up and rise only at dusk. The ZAP therefore detects a dense band of acoustic reflectors that moves vertically through the water column twice a day.

Ocean Acoustics

rlat@uvic.ca — Fri, 16 Aug 2013 21:50:44 +0000

In the terrestrial world, we rely heavily on optics and our vision, and less so on acoustics and hearing. In the ocean, the opposite is true. In coastal waters, light only travels relatively short distances (5-20m), so marine animals use light for sensing only the very near-field environment, while sound can travel huge distances (1-1000km), and informs marine animals of distant features and events. Marine scientists also take advantage of the efficiency with which sound travels in the ocean, and use it to both investigate and listen to phenomena over long distances.

Waves can take on many forms, such as the surface gravity waves on the ocean, transverse waves along a string, electromagnetic radio waves in the atmosphere, or compression sound waves. When a medium (gas, liquid, or solid) iscompressible, then it will support the propagation of sound waves. Here is a simple animation of a compression, or longitudinal wave. One can think of a sound wave as a perturbation of alternating regions of compressed and decompressed molecules of the medium, that propagates along, as one front of molecules presses against the next, which then press against the next, and so on. So a sound wave is a pressure wave, and although the molecules move back and forth very slightly as the wave passes by, the pressure pulse propagates a long way while the atoms remain at their original location.

Sound Wave Propagation

The more dense the medium, the fast sounds waves propagate. In the ocean, sound travels at roughly 1500 m/s, over 4 times the speed of sound in air (340 m/s). Variations in the seawater temperature and pressure (depth) also cause small variations in the speed of sound, and can result in complex and refracted propagation paths over long distances. Just as we can hear low and high sounds, sound in the ocean is made up of both low and high frequency waves. Low frequency sound physically has longer wave lengths, requires more energy to generate, and will consequently travel greater distances with little degradation. High frequency sound (i.e. >100 kHz) on the other hand has smaller wave lengths and will not propagate as far, but will allow the detection (reflect off) of smaller features. Low frequency sound is used to communicate over long distances, while high frequency sound is used to probe the local environment.

When sound encounters an obstacle, or travels through the stratified ocean, several things can happen. Upon reaching a suspended solid (plankton, fish, debris), some of the sound is scattered, either in the forward or oblique directions (diffraction) or back towards the source (backscatter). When sound encounters a fixed surface (i.e. the ocean surface or bottom), most of the sound energy isreflected. The ocean is not homogeneous, in that the sea water temperature (T), salinity (S), and density (ρ) vary in space. Consequently, the speed of sound (c), varies spatially as a complex function of T, S and pressure (P).

Active Sonar

Just as we might use a flash light to illuminate our surroundings when it’s dark, scientists use active sonar systems to penetrate into the ocean to investigate features hundreds, and even thousands of metres away. A transducer is both an underwater speaker and microphone, and is used to both transmit and receive an acoustic signal. Among the various techniques, transmitted signals can be simple monotonic pulses of sound, or pulses making up complex codes(somewhat akin to Morse code). Such pulses travel and radiate away from the transducer, reflect off of objects and structures in the ocean, and then propagate back towards the same transducer where the returning pressure waves are detected. For simple echo-sounder systems, the received monotonic echo is characterized by its intensity only, as a measure of how efficient or large the scattering (reflection) process or object was at that particular frequency. Shown above is an echo-sounder image from the Zooplankton Acoustic Profiler (ZAP) in Saanich Inlet. For more complex transmissions (i.e. from an Acoustic Doppler Current Profiler), the sequence of sound pulses make up a code whose returned integrity can be analyzed for variations such as a Doppler shift.

Passive Acoustics

Hydrophones If the receiver does not transmit but only records the received pressure waves, then it is effectively an underwater microphone, which we call a hydrophone. Hydrophones are used to research the many naturally occurring sounds in the ocean. These include wind, waves, and precipitation on the ocean surface, ship and boat engines, and marine mammals, that use acoustics to both echo-locate food and communicate. The hydrophone arrays on VENUS can consist of several co-located receivers, whose signals can be combined to form a directional antenna. The received audio signals can be converted into files for listening (i.e. MP3), or analyzed for their frequency content and displayed as a spectrogram.

Measuring Currents

dwowens@uvic.ca — Mon, 15 Oct 2012 07:00:00 +0000

Two major currents on British Columbia’s west coast, the California Current and Alaskan Current, carry water south and southwest respectively. Within NEPTUNE observatory, currents are measured using ADCPs and acoustic current meters. Each location needs to be examined independently since local bathymetry and geological features can affect the water flow.

Progressive vector diagrams use a selection of depths to visualize the large scale, general trends of current directions. Distance is not measured in this type of plot, but it is inferred from the velocity and direction of the current as well as the time interval measured. Each current vector is added onto the previous vector, starting from the (0,0) origin on a Cartesian co-ordinate grid where the instrument is located. The data are averaged over 15 minute intervals with velocities measured in m/s then converted to distance (km) on the x-y axis. The plotted line approximates the trajectory an individual water parcel might follow through time.

Magnitude frequency plots (small inset graphs) count the number of times a particular velocity magnitude occurs, at intervals of 0.01 m/s. The higher the count, the more frequently a velocity magnitude occurred. Data availability bars indicate data presence and gaps over the time period of the plot. Data gaps were ignored for the progressive vector diagrams in this report.

Autonomous Mooring at Saanich Inlet Sill

rlat@uvic.ca — Tue, 18 Sep 2012 07:00:00 +0000

On 7 September 2012, Paul Macoun and Richard Dewey headed out with the Ocean Technology Laboratory (OTL-UVic) engineers Emmett Gamroth and Jeff Kennedy to deploy a small autonomous (internally recording) mooring just inside the sill at the entrance to Saanich Inlet. The mooring includes a Seabird CTD with oxygen sensor and a 300kHz RDI Acoustic Doppler Current Profiler. It was deployed at 48 41.301N 123 30.024W in 90m of water.

This 8-month deployment will monitor the exchange flows into the inlet, quantifying the density and oxygen concentration of the deep water renewals, and, using the current profile, quantify both the periodic deep in-flows and the tidal surface exchanges. This site and data were identified at the Saanich Inlet Symposium as a key set of measurements for understanding conditions further south in the Inlet. Once the experiment is complete that data will be available to the research community.

Sediment Mix-Masters

rlat@uvic.ca — Wed, 23 May 2012 07:00:00 +0000

The seafloor is, arguably, one of the most extensive habitats on the planet and it is significantly understudied. It is home to a variety of benthic organisms that spend much, if not all, of their time on the bottom sliding along or ploughing through sediment. Some organisms are deposit-feeders that ingest sediments, absorb their organic content, and excrete faecal strings or pellets; other organisms are burrowers that actively mix sediments vertically. This process by which organisms mix up sediment, is known as bioturbation, and is ecologically important because it influences nutrient recycling and other biogeochemical processes on the seafloor.

Bioturbation has traditionally been studied using time-lapse imagery or vertical tracers (natural or artificial objects on the seafloor which become buried in the sediment through bioturbation). University of Victoria Biology MSc student Katleen Robert decided to try a new approach, using video camera recordings from an Ocean Networks Canada camera at the Pod 2 site near theUpper Slope junction box, to determine which animals were mixing surface sediments and how fast they are doing it. Working with her supervisor Kim Juniper, Katleen developed a brand new methodology for this process, using imagery from a video camera deployed at 396 m depth in Barkley Canyon. In addition to the video imagery, they made use of:

1. scans from the rotary sonar installed at this location to monitor decimetre-scale sediment structures
2. acoustic Doppler current profiler (ADCP) data, to characterize bottom water currents
3. two push-core samples in order to assess sediment grain size

There are lights connected to the cameras, however, so Katleen had to be cautious about how much she used them as some species, such as black cod (sablefish) are attracted to the lights and may congregate in such high numbers they obscure the benthic animals, or possibly alter the natural behaviours of the organisms they were trying to observe. To avoid any negative effects from light pollution, the team limited light to 1 hour per day. Within this limit, Katleen tested three observation regimes:

1. 1 continuous hour of observation (4 January - 25 February 2010)
2. Two 30 minute periods (24 March - 9 April 2010)
3. 5 minutes every second hour (15 August - 23 October 2010)

The continuous one-hour observations in January and February were used to establish which organisms were present. Camera-mounted lasers, spaced 10 cm apart, and a scaling ruler on the seafloor within the field of view were used to build a perspective grid which could be overlain on the video frames to measure organism size and rates of locomotion.

The most commonly observed animals were rockfish, flatfishes (Dover sole and Pacific halibut), skates, fragile pink sea urchins, and an orange anemone. Of these organisms, only the flatfishes and urchins were commonly observed disturbing the sediments. By monitoring their movements, Katleen determined that sea urchins were able to completely overturn the sediments in the field of view, an area of 8.8 m2, in 153 to 213 days while the flatfish took slightly longer, overturning the same area in 227 to 294 days. These numbers taken together represent sediment surface overturning completely at rates of 26.0 to 35.1 m2/year. These numbers are consistent with other observations at deeper locations in the northeast Pacific and northeast Atlantic Oceans.

Although Katleen determined that individual fragile pink urchins cause little sediment mixing, these animals are known to occasionally aggregate in high numbers, in which case they could have more intensive but localized bioturbating effects. Flatfish overturn much more sediment individually than urchins. Halibut and sole tend to burrow into the surface of the sediment and leave small oval pits about 1-2 cm deep. It is thought that they may dig these pits for protection from predators or to help them capture prey.

Researchers at Dalhousie University have discovered similar pits in high-resolution sonar images from this same site (Pod 2, near Upper Slope). These pits remained, and were not filled in, for approximately 6 months. Current metre measurements suggest that these pits were not formed by bottom currents which were rarely strong enough to re-suspend sediments and fill in the burrows. Instead, the researchers are now exploring the idea that these pits are made by flatfish that revisit them often and maintain the same pits so they do not become in-filled.

Robert & Juniper’s study illustrates the importance of animals in the deep sea are for mixing sediment, which can happen at surprisingly rapid rates. They suggest that long-term monitoring of bioturbation will provide important insights into the response of seafloor ecosystems to changes in primary productivity and related supplies of organic matter supply to the deep sea. This eventually will help scientists evaluate the impacts of global climate change and human disturbances on deep-sea ecosystems.

Storm Watching

rlat@uvic.ca — Fri, 16 Mar 2012 07:00:00 +0000

19-23 January 2012:

An intense windstorm left thousands of Vancouver Islanders out of power and forced BC Ferries to suspend service to the mainland on the 22nd. Wind gusts exceeding 110km/h were recorded in places, as a train of intense low pressure systems struck Vancouver Island's west coast one after another. Wave buoy data at the La Perouse Bank (located approximately 50km northwest of Folger Node, ISDM ID online data: C46206) showed extreme waves reaching as high as 18m on 22-23 January.

Watching from Below

Our Folger Passage node is connected to two different instrument platforms, Folger Pinnacle (25m) and Folger Deep (100m). Scientists use data from these platforms to study a variety of topics, including ocean biogeochemistry, land-ocean interactions, phyto- and zooplankton, fish and marine mammals. A recent pilot study by Ocean Networks Canada data specialist Dilumie Abeysirigunawardena found that these platforms might additionally be well-suited to study storm waves and storm impacts on ocean biology.

Deep Mixing

Data from Folger Deep revealed some interesting trends. At storm onset, oxygen concentrations increased significantly, probably due to mixing from wave action, and then levelled out. Water temperature also increased during the early stages of the storm. Salinity, on the other hand, dropped throughout the event.

When Folger Pinnacle data were examined, patterns were different than those observed at Folger Deep. Folger Pinnacle water temperatures dropped sharply at the onset of the storm. Apparently, storm waves were mixing warmer surface water downward and cool water upward from deeper layers into shallow layers. Surface cooling may have also been affected by rain water temperatures, although rain data remain to be examined.

Wind & Wave Data

An Acoustic Doppler Current Profiler (ADCP) on Folger Pinnacle platform has special wave measurement capabilities for assessing directional wind and swell waves. Although the pressure sensor of this ADCP was partially damaged, it is still able to collect data which can be corrected using other fully functional pressure sensors at this site. Having multiple sensors at one location is very advantageous, as it allows us to validate the accuracy of collected data. Secondary sensors can also be used as backup in the event a primary sensor fails at a location.

At the storm's peak on 23 January, the ADCP data from Folger Pinnacle indicated significant wave heights, reaching over 10m, with larger directional distributions of wave energy. The drop in the wind speeds from 110 to 35 km/h that day caused the wave energy to diminish substantially toward the end of the day.

Date (2012)	Wind Speed (km/h)	Wind Direction (oN)
19 January	35	100-50
20 January	71	100-275
21 January	75	270
22 January	100	100-270
23 January	110-35	160-170

The following set of plots from the Folger Pinnacle ADCP gives a detailed illustration of wave energy evolution over the day. Plot A shows the evolution of wave parameters on 23 January 2012. Early in the day, the waves were quite large and gradually diminished as the wind subsided. The thick black line marks peak wave heights from the day. Plot B shows wave energy distribution at the time marked by the thick black line in plot A. Plot C shows wave energy directions. Waves were propagating from almost all directions, but strongest energy was concentrated in the north to west quadrants. Plot D shows wave energy distribution over time. High frequencies indicate large sea waves; low frequencies indicate swell waves.

Zooplankton Distributions

Another interesting feature of the ADCP is its beam intensity data, which shows how objects like bubbles, zooplankton and fish move through the water column. Zooplankton, tiny organisms that feed on phytoplankton, typically migrate up to surface waters to feed at night when there is less of a chance of being eaten by visual predators; at dawn they descend into the depths for protection. These movements can be tracked on both our ADCP and our Biosonics echosounder at Folger. Surprisingly, these regular zooplankton migrations were apparently disrupted by the storm.

On 19 January the normal zooplankton migration occurred, but as winds strengthened on 20 January, their pattern was disrupted significantly and remained so for the rest of the storm. Even following the storm it took nearly 10 days for the zooplankton's regular migration schedule to resume. We speculate that perhaps zooplankton are not strong enough swimmers to ascend against such intense waves. Another explanation is that their food (phytoplankton) was more widely dispersed than normal. A third possible explanation is that bubbles injected into the water by the storm action masked the zooplankton signals. During some storm events, waves have been observed to drive air bubbles downward 30-50m into the water column.

Still Much More to Learn

This pilot study by our data specialist illustrates just a couple examples of some new ways scientists can use our seafloor instrumentation to study ocean dynamics and biology. We invite interested scientists to delve deeper, building on these initial observations. Contact us if you would like to know more about our instrumentation and find out how to access our data archives.

Using Sound to Visualize Currents

rlat@uvic.ca — Fri, 03 Feb 2012 08:00:00 +0000

Acoustic Doppler Current Profilers (ADCPs) are instruments used in our subsea network and other oceanographic applications to measure the currents. We collect data from two types of ADCPs, manufactured by Nortek and RDI.

These ADCPs use “sound beams” to measure water movement. Sound pulses are sent out in three or four different directions from the instrument; when sound waves strike suspended objects such as tiny particles or zooplankton, some of the energy is reflected back to the ADCP where it is detected by the instrument’s transducers. The received signal intensity gives an indication of the abundance of particles within the water. The Doppler shift of the received signal for each beam is used to determine the current velocity.

Using three separate beams, a 3D current velocity can be calculated. Some ADCPs have a fourth beam, allowing for two 3-beam calculations to be compared to gauge the reliability of the data. Also, if pings from a single beam aren't autocorrelated sufficiently (i.e. the returned echo is unreliable/ambiguous/bad/contaminated), they can be discarded and an estimate of current velocity can still be made using the other 3 beams. Some of these ADCPs also include sensors for temperature, pressure, tilt and compass heading.

Currently, we have 9 ADCPs in the water at a variety of locations. Some ADCPs are affixed to instrument platforms while others sit at the top of moorings (NW RCM and NE RCM) near our Endeavour site. During upcoming cruises this year we hope to install three additional ADCPs to our network.

Currently installed ADCPs.

Location	Depth (m)	Manufacturer	Frequency
Folger Pinnacle	25	RDI	600 kHz (+ wave sensor)
Folger Pinnacle	25	Nortek	2 MHz
Folger Deep	100	RDI	300 kHz
Barkley Pod 3	892	RDI	150 kHz
Barkley Pod 3	893	Nortek	2 MHz
Barkley Pod 1	985	RDI	600 kHz
Barkley Pod 1	986	Nortek	2 MHz
Endeavour Mooring NW	1893	RDI	75 kHz
Endeavour Mooring NE	1907	RDI	75 kHz

There are some challenges, however, in using ADCPs to measure currents. There can be acoustic returns from sources other than currents detected – for example bubbles moving through the water column or fish swimming through the beams. Additionally, nearby instruments can sometimes acoustically interfere with the ADCP. Other complications include data gaps (from when the instrument was turned off or wasn’t working, for example) or changes in sampling frequency.

The data obtained from the ADCPs reveal important information about the currents at a study site, however, such data can be difficult to present in a traditional paper publication medium. Since the data represent three dimensions over long periods of time it can be challenging to flatten them out and show them in 2D. Some of data have been successfully visualized using animations but animations are difficult to represent in a printed publication.

One way to represent current data in 2D is with progressive vector diagrams like the one shown below. Progressive vector diagrams (PVDs) use a selection of depths in order to visualize the large scale, general directions of currents. Distance is not measured in this type of plot, but it is inferred from the velocity and direction of the current as well as the time interval measured. Each current vector is added onto the previous vector, starting from a central (0,0) position on a grid. This centre point represents the instrument position. Current velocity is averaged over 15 minute intervals and measured in metres per second then converted into distance (km) on the x and y axis. In essence, it is as though an individual water parcel is being followed through time along the plotted line. We can plot multiple depths on one individual PVD.

The magnitude frequency plots (small inset graphs on the progressive vector diagrams) count the number of times a particular velocity value is measured. The higher the count, the more frequently a velocity occurs, for each depth plotted. In the diagram below, very low velocities were most common at the 1907m depth, while 0.05-0.1 m/s velocities were most common at the 1827m depth. The data availability bar at the top of the plots indicates when ADCP velocity data were collected over the 3 month period represented in the diagram.

Besides monitoring currents, scientists are using the ADCPs in our network for a variety of research projects examining everything from shallow shelf environments down to the deep-sea hydrothermal vents. At our Barkley and Folger locations, the West Coast Vancouver Island Coastal Marine Ecosystem (WCVI) project is studying primary (phytoplankton) and secondary (zooplankton) production in coastal marine ecosystems and the implications for fish and whales. Variability in water circulation and renewal of deep inlet waters can create variability in phytoplankton and zooplankton abundance and timing. ADCPs help scientists quantify the tidal, weekly, seasonal, and inter-annual variability of phyto- and zooplankton. Our ADCP at Folger Passage has an additional capability to study waves in this coastal zone.

Also in Barkley, the Barkley Benthic study aims to determine how disturbances affect deep sea ecosystems. Instrument platforms in Barkley Canyon are outfitted with ADCPs which will be used to monitor ecological and biological responses to episodic events.

The vertical profiler system POGO will be raised and lowered in the water column to generate profiles of the water using sensors which measure chemical, physical and biological properties. To help generate these profiles, the POGO instrument package will include a 400kHz current profiler.

Finally, the Monitoring Endeavour project uses two moorings to study the flux of heat and mass and the biogeochemical and physical processes associated with spreading ridges. Each mooring consists of numerous sensors, the uppermost one an ADCP. Two additional moorings, planned for installation this year, will allow scientists to develop special models describing deep-sea current circulations in this highly dynamic location.

ADCP Velocity Plots now available

rlat@uvic.ca — Tue, 06 Dec 2011 08:00:00 +0000

Although we have been collecting Acoustic Doppler Current Profiler (ADCP) data for over two years from various locations in the Strait of Georgia, real-time plots of the data have only recently been added to the Data Plots section. Shown here is a single day of data from the Eastern Strait of Georgia site, showing (top panel) the East/West component, (second panel) the North/South component, (third panel) the Up/Down (vertical) component, and (forth panel) the average back-scatter intensity.

These data are from 2 Dec 2011. The dominant signal on this day are the strong flood tides (blue in top panel/red in second panel, associated with northwest flow, (i.e. at 17:00), and relatively weak ebb tides (10:30). Occasional faint vertical banding in the vertical velocity (third panel) is an indication of internal waves, heaving the water column up (reddish) and then down (bluish). The latest 24 hours of ADCP data are available for viewing under the Data Plots section, while both plots and numerical ADCP data since 2008 are available for download.

Folger Pinnacle Frontiers

rlat@uvic.ca — Mon, 22 Aug 2011 07:00:00 +0000

The Folger Pinnacle instrument platform was installed on August 23, 2010 and connected on February 2, 2011 by a combined team of Pelagic Technologies divers, the Bamfield Marine Sciences Centre (BMSC), and Ocean Networks Canada. Since then, a wealth of data has been gathered by instruments affixed to this 23m deep platform. However, in recent months, Dilumie Abeysirigunawardena, one of our data specialists, noticed a drop in the instruments’ data quality and sensitivity. Some stopped working altogether, while signals from others have gradually diminished. (See, for example, the drop-off in irradiance from our light sensor below – you’d normally expect June to be brighter than February!)

Folger Pinnacle was not visited during our recent 3-week July cruise because it is the only site on the NEPTUNE Observatory that is serviced by professional divers; the other four nodes and the Folger Deep instrument platform (complement site at Folger Passage node; are too deep for divers and the waters at Folger Pinnacle are generally too turbulent for large remotely operated vehicles. In addition, Folger Pinnacle is a unique site, situated in a rockfish conservation zone, where sunlight penetrates to a shallow reef populated by an abundance of life.

Instrument Overview and Maintenance

We were warned by Captain John Richards of BMSC that our marker buoy was missing (again) so the first task when we arrived at location on August 2, 2011 was to install a new purpose-designed marker buoy.

On the seafloor, all the instruments desperately needed intensive cleaning due to extensive biofouling--in other words, barnacles, algae and other forms of life were taking over! This interferes with data collection as sensors and lenses become blocked.

There were 7 scientific instruments installed on Folger Pinnacle platform:

RDI Workhorse Monitor Acoustic Doppler Current Profiler (ADCP)
Nortek single-point acoustic current meter
Nortek Aquadopp ADCP
Biospherical Photosynthetically Active Radiometer (PAR) light sensor
WET Labs fluorometer and transmissometer
3D high-resolution camera imaging system and LED light array
Sidus HD video camera

We were pleased to have the expertise of Glenn Hafey and the Pelagic Technologies commercial dive crew again with us this summer. This is the dive team that previously helped us install and connect Folger Pinnacle. In addition, thanks to the BMSC scientific dive team led by Siobhan Gray who captured video footage of the operations and aided in cleaning the instruments.

When they first swam down to the platform, they thought it had disappeared. Every available surface had been colonized by reef creatures and some instruments were transformed beyond recognition.

Following specific instructions from manufacturers, divers restored some of the instruments with a multi-purpose scrub and wipe sponge, plastic spatulas, a small soft bristle brush, and cotton cleaning cloths. Zinc-oxide was smeared onto transducer surfaces to deter future biofouling, but we’re not taking any bets this won’t happen! Thanks to our intrepid dive crew, the instrument platform went through an incredible transformation and it became possible to distinguish the various instruments once again.

Camera Recovery

Two instruments did not remain with the platform. The divers retrieved the Sidus HD video camera and the 3D camera array. They also removed the bio shutter from our WET Labs fluorometer/transmissometer in a very delicate process (it apparently became stuck open when a barnacle took up residence between the copper plate and the optical surface).

The instrument recovery process with divers is much different than with ROPOS. In order to recover the 3D Camera Array and the Sidus Camera Assembly, divers had to unbolt them from the Folger Pinnacle instrument platform. Next, the divers attached lift bags to the cameras’ instrument frames and inflated them. The 3D Camera Frame weighs approximately 180 lb in water and 250 lbs in air, while the Sidus Assembly weighs approximately 19 lb in water and 30 lb in air. The bags were to make the instruments neutrally buoyant and easier to control. After that they attached a line to the camera frame, which was pulled up by the surface team led by Captain John Richards of BMSC using a capstan (a revolving vertical-axled type of pulley).

Results

After cleaning we were able to regain access to good scalar data from all instruments, including the single-point acoustic current meter, which had failed in June 2011.

The following data plots reflect the improvements seen after instrument cleaning.

1) RDI Workhorse Monitor ADCP

A clear improvement resulted for this instrument, as shown in the following two plots of beam 2 signal strength before (top figure) and after (bottom figure) the cleaning program. Average echo intensity increased from 77 counts (before cleaning) to 113 counts (after cleaning).

2) Nortek Current Meter

According to the data, beam 3 failed first. Notice that the diagnostic counts after cleaning program are well below the actual beam counts, which suggests good data. All three beams showed an increased sensitivity. Also note that the diagnostics counts (blue dots) are now well below the respective beam counts, providing sufficient gap to produces reliable current projections.

3) Nortek Aquadopp ADCP

The cleaning program improved the signal strength of all three beams on the Nortek Aquadopp profiler.

The Nortek downward-looking current profiler was performing satisfactorily even before cleaning; however, initial inspections showed significant biofouling. The dive team did some rigorous and delicate cleaning to remove bio-fouling from the transducers.

4) Biospherical PAR Irradiance

This device indicates the amount of ambient light detected at the platform (23m below the surface). Sensor sensitivity increased from almost nothing to very clear daily spikes beginning August 6, 2011.

5) WET Labs Fluorometer/Transmissometer

After the bio-shutter was removed and the instrument cleaned, the variability of chlorophyll captured jumped from zero to approximately 25 ug/l.

6) 3D high-resolution camera imaging system and LED light array

The 3D high-resolution camera imaging system is getting its lighting system repaired for redeployment in 2012. A research team led by Sally Leys and Herb Yang of the University of Alberta will use the custom-built 8-lens camera system to make 3D images of sessile (non-mobile) suspension feeders living beneath the platform.

7) Sidus HD Video Camera

The Sidus video camera was intended to provide a live video spyglass for researchers studying the rich ecosystem inhabiting Folger Pinnacle Reef. Unfortunately, the camera did not function properly, and will be replaced.

(More than) a Little Help from our Friends

All in all, the 3-day cruise was a great success! We are now implementing a regular cleaning and inspection program. We wish to thank both BMSC and Pelagic for their tremendous assistance with this important work!

July 2011 Expedition Comes to an End!

rlat@uvic.ca — Fri, 29 Jul 2011 07:00:00 +0000

From July 4 - 25, 2011, Ocean Networks Canada navigated an impressive installation and maintenance expedition in the northeast Pacific Ocean. Diving down to the seafloor to investigate our 800-km cabled network observatory along the northern Juan de Fuca plate, we tended to our technically-advanced instruments and witnessed some of the amazing marine life dwelling off the coast of Vancouver Island, British Columbia.

THE JOURNEY

Aboard the R/V Thomas G. Thompson (University of Washington), we completed 33 dives at all 5 active node locations. Our route was

Cascadia Basin (2660 m depth)
Endeavour (2300 m depth)
Clayoquot Slope (1260 m depth)
Barkley Canyon (396 - 981 m depth)
Folger Passage (100 m depth)

Fortuitously, smooth seas and astute judgement hailed the ship around for a second pass, returning it to Barkley Canyon, Endeavour and ODP 889.

THE PEOPLE

Many thanks to the crew of the R/V Thompson for their wonderful hospitality and excellence in operating this world-class research vessel. In addition to the ship’s crew, our full complement included the 9-man ROPOS team, 2 visiting IFREMER technicians, 3 University of Washington technicians, 2 contractors, 5 university students, and 6 Ocean Networks Canada staff members. Under the guidance of Chief Scientist Lucie Pautet and Co-chief Scientist Marjolaine Matabos, we accomplished many of our objectives and improvised supplementary dive plans to enhance our time at sea and to finish some tasks slated for the upcoming September expedition.

Onshore staff also kept busy commissioning newly-installed and redeployed instruments, trouble-shooting access to live video on our website, and updating both scientists and the public on unfolding events. One great example of cooperation between ship and shore occurred during the final dive of the expedition, when we managed to restart high-quality data recording at the currently autonomous CORK U1364 at ODP 889. Quick thinking on the shore by Robert Meldrum (Geological Society of Canada), Earl Davis (GSC), John Bennest (contractor), and Martin Heesemann (Ocean Networks Canada [ONC]), with Martin Scherwath (ONC) and Reece Hasanen (ONC) testing and practicing the procedure on the ship, led to a revival procedure for this Integrated Oceanic Drilling Program (IODP) CORK. Data analysis showed that 1 sensor had a leak, compromising the entire CORK, so ROPOS cut the cable to the faulty sensor. The maneuver worked and the data logger became accessible again and could be reprogrammed. There is now data recording on 4 pressure gauges.

THE HIGHLIGHTS

In our 21 days at sea, we

Installed 15 instruments;
Redeployed 4 instrument platforms and 11 instruments;
Recovered 2 instrument platforms, 26 instruments, Wally the Crawler(carries an additional 7 instruments), and 9 km of electric-optic cable;
Repaired IODP CORK U1364A and successfully downloaded data;
Surveyed areas to lay down new cable during our next expedition.

On top of all this maintenance, we gathered 117 samples during 21 of the 33 dives and at nearly every visited location. When our science crew arrived at the Esquimalt Graving dock, we greeted them with a car full of coolers! The principal investigators and their research teams will analyze the samples, which included:

Tubeworms
4 scoop samples
20 water samples
28 Niskin bottles
65 push-core sediment samples

One of the major objectives of the expedition was to investigate the power outage at Barkley Canyon that occurred on February 18, 2011. Site inspection showed instrument and cable damage at Barkley Upper Slope and Barkley Benthic Pod 2, which may have been caused by a trawl hit. All equipment was accounted for and the end of the main extension cable was recovered, sealed, and will be re-terminated. Actual repair is planned for 2012. The 2 instrument platforms and a number of instruments were brought back for further repair. At this point, we stand to lose over a year of unique and valuable data from this benthic environment. Furthermore, we were forced to delay deploying the Vertical Profiler System (VPS), which consists of a seafloor platform and a motorized tethered float that serves as a host to a collection of instruments for monitoring processes in the water column.

THE ACTION

Cascadia Basin

Piezometer installed and data running.
Auxiliary platform installed.
Conductivity-Temperature-Depth sensor (CTD) swapped for re-calibration.
3 bottom pressure recorders (BPR) recovered.

Endeavour

Recovered benthic and resistivity sensor (BARS).
Final troubleshooting of last October’s loss of communications with theMain Endeavour Vent Field: the junction box was found to be operational identifying the cable as the faulty element, which will be replaced during the September 2011 expedition.
In-situ testing of Cabled Observatory Vent Imaging Sonar (COVIS) and Remote Access Water Sampler (RAS) confirmed operational status.
Inspected Tempo-mini site; installation delayed to September 2011 when site can be powered by a new cable.
Surveyed Mothra and future mooring sites.
Recovered 5 km of a 6 km failed cable at MEF and all 4 km of the cable at Regional Circulation Mooring North (RCMN).

Clayoquot Slope

Recovered the multibeam sonar.
Deployed CTD.
Retrieved data from IODP CORK U1364A, and made a repair so that it is now recording data on 4 pressure gauges.

Barkley Canyon

Attempted to deploy temperature probes at Barkley Hydrates; however, due to subsequent technical problems, the instrument had to be recovered.
Recovered Upper Slope Instrument Platform and Barkley Benthic Pod 2, as well as their associated instruments.
Recovered and sealed the Upper Slope extension cable.
Recovered, cleaned, inspected, and redeployed Pods 1, 3 and 4.
Added the RDI Acoustic Doppler Current Profiler (ADCP) from recovered Pod 2 and redeployed at Pod 1.
Swapped the hydrophone at Pod 1.
2 Nortek Aquadopps moved from Pods 1 and 3 to separate auxiliary platforms to reduce interference with other acoustic instruments.
Recovered 2 Kongsberg rotary sonars from Pods 1 and 3 for refurbishing for future redeployment.
Swapped 2 camera pan-tilt systems due to corrosion at both Pods 1 and 4.
Connected a sediment trap to Pod 3.
CTD swapped for calibration at Pod 4.
Recovered Wally II for maintenance; however, technical problems precluded immediate redeployment. Repair is underway and the plan is to redeploy Wally II in September 2011.

Folger Passage

Replaced BPR, ADCP and hydrophone at Folger Deep.
Folger Deep Instrument Platform recovered, cleaned and redeployed.

THE FUTURE

Principal investigators will analyze their samples and watch the data stream in from their newly-deployed and recalibrated instruments. We will reflect on the efforts of this expedition and continue preparations for the next one, which is scheduled to embark on September 9, 2011. In the meantime, you can watch our high-definition dive videos on SeaTube (login required), look for highlights on our YouTube channel, and browse through some of the outstanding photographs we gathered on Flickr.

Ocean Networks Canada - adcp

Ocean Properties

Bottom Animal Behaviour

Conductivity

Currents

Density

Depth

Salinity

Temperature

Water Clarity

Zooplankton Behaviour

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Ocean Acoustics

Sound Wave Propagation

Active Sonar

Passive Acoustics

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Measuring Currents

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Autonomous Mooring at Saanich Inlet Sill

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Sediment Mix-Masters

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Storm Watching

19-23 January 2012:

Watching from Below

Deep Mixing

Wind & Wave Data

Zooplankton Distributions

Still Much More to Learn

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Using Sound to Visualize Currents

Currently installed ADCPs.

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ADCP Velocity Plots now available

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Folger Pinnacle Frontiers

Instrument Overview and Maintenance

Camera Recovery

Results

(More than) a Little Help from our Friends

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July 2011 Expedition Comes to an End!

THE JOURNEY

THE PEOPLE

THE HIGHLIGHTS

THE ACTION

Cascadia Basin

Endeavour

Clayoquot Slope

Barkley Canyon

Folger Passage

THE FUTURE

Thank you to everyone who made the expedition possible!

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