Coastal observatories are critical windows on the marine environment
Sustained observations of the coastal ocean and atmosphere are critical for both understanding the marine environment and its role in our weather, climate, and coastal resources. With 50 percent of the earth’s population living within a hundred miles of a coast; severe beach erosion, storm impacts, spills, coastal development, nearshore fisheries, harmful algal blooms, and the changing marine weather are all important societal issues that require sustained observations and research.
For example, coastal engineers and planners have been concerned with coastal protection, particularly in heavily populated areas where wave attack, set up, and shoreline erosion threaten coastal structures. Geologists have been struggling to understand how the astonishing variety of coastal geological features form and evolve in response to nearshore processes. Coastal meteorologists are only now beginning to investigate physical processes that are unique to the coastal environment, including the adjustment of the near-surface winds to extreme changes in the surface roughness, differential heating, and the creation of sea spray in the surf zone.
It is nearly impossible to understand these complex and dynamic processes that occur at the interfaces where the ocean meets the atmosphere and where it meets the shore without sustained observations.
Sampling from ships, buoy systems deployed for long time periods, or drifters are always limited by the amount of on-board power or data storage available, as well as time. In contrast, continuous sampling at stable permanent platforms gives us data to clarify patterns and allow development of predictive models for interactions of phenomena such as storms, seismic events, and toxic algal blooms. Coastal observatories with real-time data and virtually unlimited power transmission capabilities (when compared to traditional oceanographic moorings) provide scientists with continuous access to the coastal ocean.
The Woods Hole Oceanographic Institution (WHOI) has played a leading role in designing, deploying, and maintaining cabled ocean observatories.
The MVCO design is focused around a ‘node’ system, replicated at each of the observatory’s sites that allow flexible power and communications choices for supporting a wide range of sensors. By design, scientists can access their data and instruments in real-time, adjusting sampling parameters based on changing field conditions, extending our reach into the ocean on a sustained basis.
The history of MVCO
MVCO was created by WHOI scientists in 2001 to carry out sustained observations of the coastal ocean and atmosphere as well as to provide an infrastructure that could support future process studies of the marine environment.
Led by Jim Edson and John Trowbridge, scientists within WHOI’s Applied Ocean Physics and Engineering Department, WHOI worked to design, build, and commission the observatory throughout 2001 to 2003. Construction of the shore lab, meteorological mast, seacable, and underwater node was funded by the National Science Foundation. Construction of the Air-Sea Interaction Tower offshore was subsequently funded by the Office of Naval Research in 2003. Since installation, MVCO has been maintained continuously by WHOI as a facility for basic and applied science research.
How was MVCO built?
The shore laboratory located at Katama Air Park is the termination point for the fiber-optic power cable. It contains the computer systems and power supplies necessary for controlling the sensors and logging the data locally. A 10-meter mast extending above the laboratory holds sensors to measure solar and infrared radiation, rainfall rate, temperature, humidity, wind speed and direction. The shore laboratory is connected to WHOI via a high-speed wireless radio and a commercial leased-line as back-up. The laboratory includes an automatic backup-power generator to continue operation of the entire system during power outages. All computer and equipment operations are monitored remotely from WHOI.
Cable description and installation
The seacable consists of six AWG13 copper power conductors, with high voltage insulation. Ten single-mode optical fibers are contained in a loose-tube assembly at the center of the cable. The core is jacketed with a polyurethane sheath protected by two layers of cross-laid armor wire and a polyethylene outer jacket.
To cross the beach area with the least environmental impact, WHOI utilized directional drilling technology. The drilling operation provided a steel conduit, 626 meters in length, between the airfield and the seafloor (approximately 300 meters from the beach in about 3 meters water depth). A second conduit (206 meters in length) was drilled to provide a cableway to the meteorological sensor mast located on the beachfront next to Donnelly House.
The cable was then pulled back through each conduit and connected to a junction box on the airfield and then to the lab. The offshore cable was laid on the bottom, then jetted under the sand using an underwater cable jet-plow.
The Sea Node
At the 12-meter isobath, approximately 1.5km south of the Edgartown Great Pond is the instrument "node". The node consists of a 12" diameter steel pedestal jetted into the bottom with a four-foot square instrument frame sitting on top. The node contains all the electronics for connecting the scientific instruments and sending the data back to shore. Divers can mount instruments on or near the node and simply plug into an underwater connector that will provide power and two-way data communications.
The Air-Sea Interaction Tower (ASIT)
The Air-Sea Interaction Tower was completed in the summer of 2002 about three kilometers from shore along the 15-meter isobath. The tower is equipped with a 19-port node providing power and two-way data communication to shore. In July 2003, a beam was installed between two legs to provide a platform at four meters below mean sea level. Users can reach the node top-side by climbing to a platform, which is 12 meters above sea level. A met mast was mounted to provide air-side observations to 10 meters above the service platform or 22 meters above sea level.
Since its inception, MVCO has supported continuous observations of the ocean and atmosphere as well as numerous short term process studies, including the Office of Naval Research-sponsored Coupled Boundary Layer and Air-Sea Transfer program (CBLAST) and the Ocean Horizontal Array Turbulence Study (OHATS), numerous NSF-sponsored experiments on air-sea fluxes, stresses, and exchange, as well as the first successful attempt to directly and simultaneously measure the heat and momentum exchanges on both sides of the air-sea interface.
The Air-Sea Interaction Tower (ASIT), operating since 2003, is the only fixed structure within U.S. coastal waters suitable for detailed studies of air-sea interactions and observations of the exchange of heat, momentum, and gases between the ocean and atmosphere.
The ASIT has served as a national test site for a wide swath of advanced oceanic and atmospheric sensors and sensing platforms since its commissioning. As an example, the ASIT hosted the first successful implementation of high frequency (HF) radar sensing of oceanic surface currents from a fixed, metal, offshore structure, which is now being replicated on oil and gas platforms of opportunity in the Gulf of Mexico. Numerous researchers have utilized the facility for scientific studies or experiments, from critical experiments focusing on the coupled air-sea boundary layer, to more recent efforts relevant to offshore wind energy.
Since its inception, the shore meteorological mast and ASIT has been continuously occupied, making observations for both short term, intensive oceanic and atmospheric studies as well as long-term monitoring of the marine environment for general scientific use. Data from the core sensors deployed on the ASIT are routinely ingested into NOAA National Weather Service real-time datasets.
Upgrades and developments
The observatory has undergone a series of upgrades and major maintenance operations since its creation. The ASIT steel structure has been fully repainted numerous times. The individual nodes, both underwater and air-side have been regularly serviced and repair, and much of the electronics have been replaced. Notable upgrades include:
The ASIT landing platform was redesigned and fully replaced in 2009 to give a larger, safer landing pad for crew members to board the tower from service vessels. This also increased the weather window in which tower operations could be conducted.
The 2018-2019 overhaul
After 15 years of continuous use, the sea cables connecting the underwater node to the ASIT were in serious shape. Years of strong tidal currents, and the pounding waves of winter storms had finally infiltrated the shielding of the cables, exposing the delicate communications fibers and power-providing copper wires to the salty ocean. In the fall of 2018, WHOI worked to lay a new cable between the node and ASIT, in order to revive the observatory and extend its life. Issues with the installation prevented repowering the observatory until May 2019, when contractors could repair a damaged underwater splice.
However, this additional time was used to fully upgrade the power system of the ASIT and the underwater node, resulting in increased available power at these sites for larger, more complex instruments. The cable replacement improving the speed and reliability of power and communications at the ASIT as well as and make improvements touching much of the infrastructure.
WHOI continues to operate the MVCO as a service to the greater research community. The end of life date of the ASIT and sea-cable is expected to be 2030.