Ships at sea: Enabling marine observations.

Over 150 years of ships keeping watch

3,000+

ships contributing observations worldwide

3

networks - VOS, ASAP and OceanTraX - coordinated

170+

years of continuous marine data, dating to Brussels 1853

The ocean covers more than two-thirds of our planet's surface. Understanding it - and the atmosphere above it - is fundamental to everything from daily weather forecasts to long-term climate science. Yet for most of Earth's history very little was known about this vast space. Ships changed that.

For over a century, vessels crossing the world's ocean have been doing more than carrying cargo and passengers: they have been acting as humanity's eyes at sea. The Ship Observations Team (SOT) - a joint programme of the World Meteorological Organization (WMO) and the Intergovernmental Oceanographic Commission (IOC) of UNESCO - coordinates this global effort, bringing together three of the most enduring and impactful marine observation networks in existence: the Voluntary Observing Ship (VOS) Scheme, the Automated Shipboard Aerological Programme (ASAP), and OceanTraX (formerly XBT SOOP).

Together, these networks collect the surface meteorological, upper-air, and upper-ocean observations that fuel numerical weather prediction, climate monitoring, marine safety services, and ocean science - No data from satellites or autonomous systems can fully replace the marine observations provided by these networks.

Three networks. One mission.

Voluntary Observing Ship (VOS) Scheme

Every day, around 2,000 ships of various types and sizes observe the weather at their location and transmit those observations in near real time to national meteorological services worldwide. The VOS Scheme and its predecessors have been operating for more than 170 years and it remains irreplaceable. Ships and their crews measure atmospheric pressure, wind, temperature, humidity, sea surface temperature, waves, sea ice, and providing ground truth that satellites and models cannot replicate.

Learn about VOS

Automated Shipboard Aerological Programme (ASAP)

Atmospheric processes vary continuously with altitude, making vertical observations indispensable for accurate weather prediction. ASAP stations aboard merchant ships and research vessels launch weather balloons from the open ocean, collecting vertical profiles of temperature, humidity, pressure and wind from the surface to 30 kilometres altitude - filling a critical observation gap over oceans where no land-based radiosonde stations can provide this data. Around 21 ships currently provide these critical upper-air soundings, concentrated in the North Atlantic and expanding globally.

Learn about ASAP

OceanTraX Network (formerly XBT SOOP)

Beneath the surface, the ocean holds answers to some of the most important questions in climate science. OceanTraX deploys expendable bathythermographs (XBTs) and thermosalinographs (TSGs) from vessels of opportunity - including merchant and research vessels - on regular routes, measuring upper ocean temperature and salinity down to nearly 1,000 metres. Approximately 60 active ships deploy around 19,000 XBTs each year on 36 repeat sampling lines across the world's ocean basins.

Learn about OceanTraX

Improving the safety of life at sea

Improving the safety of life at sea

The International Maritime Organization Circular on Participation in the WMO Voluntary Observing Ships Scheme (IMO MSC Circular 1293) states that the value of ship-based marine meteorological and oceanographic observations to maritime safety cannot be overstated. For over a century, these reports have provided the real-time feedback weather forecasters need to improve the quality of warnings issued through the Global Maritime Distress and Safety System (GMDSS) as required under the Safety of Life at Sea (SOLAS) Convention. Formal investigations into major maritime disasters have underscored how vital these observations are in ensuring the safety of ships, their crews, and their cargoes.

Despite the rise of satellite technology, ship-based data remains essential for "ground-truthing" and providing critical information that satellites cannot observe, such as atmospheric pressure and sub-surface ocean measurements. In "data-sparse" areas, like the polar regions, a ship's report may be the only data available to forecasters. Even if a ship's journey through these regions is temporary, every observation provided is of immense value.

The ocean in real time - find our ships

The SOT maintains a live map of all active VOS, ASAP, and OceanTraX platforms through OceanOPS - the operational coordination and monitoring centre of the Global Ocean Observing System. See the map below to explore where ships are operating today, what they are measuring, and how the global network covers the ocean.

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Click to access the full-screen map

A challenge anyone with a vessel can help solve

There is currently a stark imbalance in global weather observing: we have 15 times fewer data over the ocean than over land to help predict the weather worldwide. The consequence is real - marine forecasts are less accurate than land forecasts, storm warnings over the ocean are harder to issue with confidence, and climate models carry larger uncertainties in ocean regions.

Ships already crossing the ocean are the most practical solution we have. Whether your vessel operates you are sailing through data-sparse regions where every observation counts.

The SOT provides the expertise and the international framework to put your ship's journey to work at science and to support the observing networks.

Join the VOS Scheme

Ships of all types and sizes are welcome. Your officers/crew members are already watching the weather - with a small additional step, those observations become part of a global record and feed directly into the numerical models that produce today's forecasts. Help close the gaps in our global records and enhance safety services for all mariners.

Contribute to ASAP

Does your vessel operate regular ocean crossings? ASAP stations aboard ships launch weather balloons that profile the atmosphere from the surface to 30 km altitude. With equipment installed and maintained at no cost to you, your ship fills a gap that no land-based station can reach. Atmospheric profile observations have high impact on weather forecasting and marine services.

Participate in OceanTraX

Does your ship operate on a regular oceanic route? You may be the ideal candidate for hosting an XBT sampling networks. Scientists and technicians handle the technical details - you provide the platform and the route. Help them study ocean and climate changes by deploying XBTs to acquire temperature profiles. These measurements are vital for seasonal weather, climate and ocean current prediction.

We are all connected by the ocean. Join the network that keeps watch.

Events

Workshop

Date Icon 22/09/2026 - 24/09/2026

Place Icon Shanghai, China

8th International Port Meteorological Officers (PMOs) Workshop

Webinar

Date Icon TBD

Place Icon Online

TBD

Meeting

Date Icon 13 - 16 April 2027

Place Icon Noumea, New Caledonia

14th session of the Ship Observations Team (SOT)

Click here for past meeting and events.