StoriesPlace: Ocean

The ocean below the surface

Most of the ocean’s heat lies below what satellites can see. Profiling floats drifting at depth and surfacing to report have measured it routinely since the start of this century¹; satellites measure the surface they come up through.

Systems: Profiling floats, Moored buoys, Satellite altimetry
Toward 2030: The Ocean Decade, 2021 to 2030
Figures: 4, field scene, map story, simulator, timeline to 2030

Go to the references

01Field scene

A buoy, a float and a satellite.

A moored buoy reports the surface; a profiling float drifts at depth, rises through the water column measuring temperature and salinity, and transmits from the surface; a radar satellite passes overhead. Each sees a different slice of the same ocean.

Figure as text: A buoy, a profiling float and an Earth-observation satellite

A wireframe sea surface with a moored buoy, a profiling float and a synthetic aperture radar satellite above, joined by dashed red links.

Moored buoy
Profiling float
Radar satellite

02Map story

The surface, mapped from orbit.

The SWOT mission, launched in December 2022, maps sea-surface height in wide swaths from an orbit about 891 km high at 77.6° inclination². Its ground track repeats, so the same ocean is measured again and again.

Figure as text: A wide-swath altimetry orbit over the ocean

A wireframe globe centred on the North Atlantic with an altimetry orbit, its ground track and two labelled ocean observing sites.

North Atlantic float array (40.0° N, 35.0° W)
South Atlantic (25.0° S, 20.0° W)

03Simulator

Getting a few kilobytes home.

A float surfaces for minutes. Whether its profile gets out depends on which satellites are above the horizon, and for how long. The footprint and delay of a relay satellite follow from its altitude and the elevation mask³.

Figure as text: Footprint of a low-orbit data relay

A section through the Earth with a low satellite and its footprint arc in red.

Footprint of a low-orbit data relay, at the starting values
Altitude	780 km
Elevation mask	10 °
Footprint radius	2,076.1 km
Slant range at the mask	2,324.6 km
One-way delay, nadir	2.60 ms
Bent-pipe delay, user to gateway	15.5 ms
Orbital period	100 min

04Timeline to 2030

An ocean decade.

The United Nations declared 2021 to 2030 the Decade of Ocean Science for Sustainable Development⁴; the Global Ocean Observing System’s strategy sets out what an observing system fit for it must deliver by 2030⁵.

Figure as text: Ocean observation milestones

A timeline from 2000 to 2030: the earliest profiling floats, the GOOS 2030 strategy, the start of the Ocean Decade and the launch of SWOT.

2000 Profiling float array begins. Floats deployed toward a global array of temperature and salinity profiles.¹
2019 GOOS 2030 Strategy. What the global ocean observing system must deliver by 2030.⁵
2021-01 Ocean Decade begins. Ten years of coordinated ocean science.⁴
2022-12 SWOT launched. Wide-swath sea-surface height from orbit.²
2030 Ocean Decade ends. The decade’s outcomes fall due.⁴

Figure 1

Field scene

Buoy mast to a ship mast: 26.7 km

Figure 1. A buoy, a profiling float and an Earth-observation satellite. A wireframe sea surface with a moored buoy, a profiling float and a synthetic aperture radar satellite above, joined by dashed red links.

References

Argo: a global array of profiling floats. Argo Program, University of California San Diego, 2024.
Surface Water and Ocean Topography (SWOT) mission. National Aeronautics and Space Administration and Centre national d’études spatiales, 2022.
Fundamentals of Astrodynamics and Applications, 4th edition. Vallado, D. A., Microcosm Press, 2013.
United Nations Decade of Ocean Science for Sustainable Development (2021–2030). UNESCO Intergovernmental Oceanographic Commission, 2021.
The Global Ocean Observing System 2030 Strategy. Global Ocean Observing System, 2019.

Where this applies

Sensors & instruments Space and satellite systems Earth observation & GeoAI Data & licensing Oceans Climate Research Transport Field tour: offshore ocean