Observing the open ocean: a reference design

01What needs observing at sea

Open-ocean observing feeds weather forecasts and warnings, climate records and the safety of everyone at sea. The global ocean observing system coordinates sustained observations of climate, ocean health and the conditions behind forecasts and early warnings¹.

At the surface, the variables that matter most are wind, air pressure, air and sea temperature, and the state of the sea. Moored buoys run by a national weather service measure pressure, wind, air and sea temperature, and wave energy spectra from which wave height and period are derived².

Below the surface, temperature and salinity reveal how much heat the ocean stores and where it moves. An international programme measures them with a fleet of robotic floats that drift with the currents and move between the surface and mid-water³.

Buoys of several kinds share the work. An international panel coordinated by the meteorological and oceanographic agencies manages networks of drifting buoys, moored buoys and tsunameters, each with its own role⁴.

The reference design brings two of these together, a moored met-ocean buoy on station and a profiling float nearby, both reporting through a satellite overhead.

02Placing instruments on station

At sea, siting means choosing a hull and a mooring. A weather service that operates moored buoys picks the hull for each location and measurement need, and designs each mooring for its hull, place and water depth².

The smallest discus hull is easy to transport and cost-effective, while the larger discus hulls offer the long-term survivability it lacks, so cost and survivability are weighed station by station². A buoy that capsizes or drags its anchor in the storm it was meant to measure has failed at its main task.

The float needs no mooring. It is launched from a ship, settles at a pre-set depth, then dives deeper and rises to the surface, measuring as it climbs³. Its position at the surface is fixed by satellite navigation on most floats in the array⁵.

Because the float drifts, its record is a series of profiles at changing positions. Every profile must therefore carry where it was taken, as well as when, or it cannot be compared with the buoy or with the next profile.

03Power is the hard constraint

Offshore there is no grid, so every sample and every message is paid for from a battery that sun, wind or a service visit must refill. Energy decides how often the instruments measure, how much they process on board and how often they report.

Operators therefore sample in bursts rather than continuously. One national buoy network notes that recording continuously drastically increases power consumption, so most of its buoy measurements use an eight-minute acquisition period⁶.

Processing moves on board for the same reason. Wave measurements come from the motion of the hull; the buoy's processor turns that motion into a spectrum, and the raw motion data are not sent ashore⁷.

A float runs on batteries alone. Its pump moves oil to change buoyancy, it repeats a ten-day cycle of diving and surfacing, and its mission ends when the batteries are exhausted³. The simulator shows how storage, load and charging set a buoy's margin through a run of dull days.

04From sensor to forecaster

A buoy or float reaches shore through a satellite. Most floats now use a satellite service that sends detailed profiles in less time at the surface and allows two-way commands, while older floats need between six and twelve hours at the surface to report⁵.

Ashore, profiles pass through quality checks at regional centres and are then served from two global data centres, with most real-time data meant to be available within twelve hours³. All of these data are free and open to anyone³.

Weather data from buoys also join the global exchange of meteorological observations, which is moving to open web standards and a subscribe-and-notify model⁸. A forecaster, a ship router and a climate scientist can then draw on the same observation.

05What travels with each value

An ocean value is only useful with its time, position, sensor and quality. The time matters precisely, and one buoy network reports the end of each acquisition period as the official observation time⁶.

Quality control starts with simple checks and grows from there. One buoy network screens real-time data for transmission errors, range limits and continuity, compares duplicate sensors and checks that battery voltage is adequate for pressure readings⁹.

Flags carry the result to every user. A national programme publishes manuals for real-time quality control of ocean variables, including waves, wind, temperature and salinity, and a manual on how to mark data with quality flags¹⁰.

06When the link is not there

At sea, a missing link is the normal state between satellite passes, not an emergency. The reference design treats every instrument as a store-and-forward node that keeps its observations until a link is available.

If a pass is missed or a message is corrupted, the buoy keeps sampling and the float keeps cycling. Stored values are sent on with their original times, so the shore record fills in late rather than leaving a hole.

When a sensor degrades, the honest answer is a flag or a gap. One buoy network removes data from a degraded sensor before posting it and instructs real-time processing not to release it⁹.