VOS Scheme

Lieutenant Matthew Fontaine Maury of the U.S. Navy was the first man to realise the scientific and commercial value of weather information collected from ships. Owing to his initiative, the first International Meteorological Conference was held in Brussels in 1853 to consider international cooperation and a uniform system of observation.

With the advent of radio communications early in the twentieth century it became possible for observations from ships to be transmitted to meteorological offices ashore, and warnings of dangerous conditions to be transmitted to ships.

At the 1929 meeting of the International Convention for the Safety of Life at Sea (SOLAS), provision was made for the international encouragement of meteorological work at sea. The current Solas Convention was adopted in 1974.

Meteorological services of most maritime countries made arrangements with ships regularly visiting their shores to take marine meteorological observations and transmit them to shore at no cost to the ship. The observations themselves are usually provided free of charge by shipping companies in return for the instrumentation and the forecasting and warning service. Hence the name of the scheme - Voluntary Observing Ship (VOS).

» View the VOS brochure (PDF, 907 kb).

Meteorological data are required from the seas and oceans for a number of purposes:

• For the preparation of forecasts and warnings to help route ships, and to avoid severe weather conditions such as those that caused the movement, and potential loss of containers from the merchant vessel in the photograph at right;
• For the preparation of forecasts and warnings for offshore industries;
• For marine consulantancy;
• For global computer models of the future state of the atmosphere;
• To monitor the state of the oceans using delayed-mode data in weekly and monthly analyses;
• For climatological data banks for many purposes, e.g. design of ships and structures at sea, determination of economic shipping routes; and
• To build long-term records to monitor changes in the climate of the earth.

The data required pertain to the atmosphere above the sea (temperature, dew point, cloud, weather, visibility, pressure) and the surface of the sea (temperature, waves, currents, ice).

The requirements for forecasts and warnings are specified by the World Weather Watch of WMO, which is managed by the Commission for Basic Systems (CBS). CBS also has responsibility for implementing the Global Telecommunications System (GTS) through which the data are distributed, as well as the Global Data Processing Ssystem (GDPS).

The requirements for monitoring change in climate have been specified by the Ocean Observations Panel for Climate (of GOOS / GCOS / WCRP), within the context of the Climate Module of GOOS (which is the Ocean Module of GCOS).

The desirable observational network for climate monitoring purposes was specified in the Final Report of the Ocean Observing Systems Development Panel (OOSDP) in 1995, and revised in the Action Plan for Global Ocean Observations for the GOOS/GCOS in 1998. This, and the desirable observational network for World Weather Watch are shown in Table 1. The spatial and temporal resolution of observations required for climate is coarser than for weather forecasting.

The oceans cover about two-thirds of the surface of the earth, and for decades ships were the only means of obtaining meteorological data from them. Although there are now several other means - satellites, drifting buoys and floats, radar - ships still play a very important part. They provide ground truth for the calibration of satellite observations and make measurements not yet obtainable by other means, such as air temperature and dew point.

There are three types of ships in the VOS Scheme:

• Selected ships;
• Supplementary ships; and
• Auxiliary ships

A selected ship is equipped with sufficient certified meteorological instruments for making observations, transmits regular weather reports and enters the observations in meteorological logbooks. It should have at least a barometer, a thermometer for sea-surface temperature, a psychrometer and a barograph. Most of the VOS are selected ships.

A supplementary ship is equipped with a limited number of certified meteorological instruments for making observations, transmits regular weather reports and enters the observations in meteorological logbooks.

An auxiliary ship is without certified meteorological instruments and transmits reports in a reduced code or in plain language, either as a routine or on request, in certain areas or under certain conditions. Auxiliary ships usually report from data-sparse areas outside the regular shipping lanes.

Ships are recruited by Members of WMO, usually through a Port Meteorological Officer, who recruits ships of all flags, not just those on the national register, into the national VOS Fleet (VOF). Ships are recruited on the basis of the willingness of the ships' officers to perform the observations and the regular route followed by the ship. A Member will generally recruit ships which regularly visit ports in the country concerned. Recruited ships are usually on the national register of the Member, but may be on a foreign register, in which case the meteorological service of the country of registry is informed.

Ship's observations are made at the standard synoptic hours of 0000, 0600, 1200 and 1800 UTC and are sent to a meteorological service as soon as they are made, either by radio telephony to a coast radio station, by telex over radio, or by INMARSAT-C. In each case the cost of transmission is paid by the meteorological service of the receiving country. With the cessation of radio telegraphy in many parts of the world in 1999, INMARSAT is the prime means of transmission of ship's observations. INMARSAT transmission allows all observations to be transmitted immediately, whereas transmission by radio telegraphy could only be done during the hours of duty of the ship's radio officer.

A list of all VOS and their instrumentation is kept up to date by the Secretariat of WMO, and included in the WMO No. 47, on the basis of information supplied by Members. Metadata, including full details of the observational site (e.g. height and exposure of the instrument), are absolutely essential to a correct interpretation and use of the observations.

Marine meteorological observations are recorded on board most ships in special meteorological registers (logbooks) provided by national meteorological services. The logbooks are collected by the Port Meteorological Officer of the recruiting country and the observations are transferred from the logbooks to magnetic media, in a standard, internationally agreed, format. Increasing numbers of ships are being equipped with personal computers and software which stores the observations on diskette in the internationally agreed format. This avoids data transfer from logbook to magnetic media as a possible source of error.

The data are then sent, at approximately three-month intervals, to global collecting centres in Germany and the United Kingdom. These centres ensure that minimum quality control has been applied to the data, and then, every three months, supply data to eight Members, each with a specific area of responsibility for the preparation of climatological summaries.

» View the JCOMM data management diagram.

PMOs visit VOS calling at their ports to check the instrumentation, calibrate the barometer, supply stationery such as barograph charts or logbooks as required, and discuss any observational problems with the Master and officers.

The quality of VOS reports is monitored by several major meteorological centres, primarily the Met Office, United Kingdom. Results of this monitoring are compiled and distributed at monthly and six-monthly intervals to PMOs, who are expected to take follow-up actions to correct deficiencies.

In order to reduce the workload on ships' officers, several means of automation of the observations have been developed. In one form, such as TurboWin, the observations are still taken manually but then entered into a personal computer which then calculates the true wind, the mean sea level pressure (correcting for the height of the bridge) and the dew point. The computer can perform simple quality control, code the observations in a manner ready for transmission by INMARSAT, and format the observation in logbook format for digitisation.

Many national meteorological services are installing automated systems on ships, however this poses a number of problems. The proper locations for sensors are not easy to find, particularly for wind and dew point. Most sites for the anemometer sensor will be affected by wind flow distortion over the superstructure, and wind speed needs to be corrected to the standard level. The equipment for automated measurement of visibility, weather, clouds and wave height can difficult to accommodate on board small ships. An additional factor is that the changing nature of international shipping creates problems in selecting a vessel that is likely to stay on the same trade route for a predetermined period. National meteorological services may therefore have a certain reluctance to invest in automated shipboard systems when there is no guarantee that a ship will continue trading in their area of forecasting responsibility.

The observations from VOS make an important contribution to the GOOS. JCOMM and its Subgroup on the VOS will work in close collaboration with the general organisation and implementation of the GOOS. Scientific advice on the VOS, particularly relating to the role of VOS observations in global climate studies, will be provided by the GOOS / GCOS / WCRP Ocean Observations Panel for Climate.

Ships in the VOS Scheme often participate in supplementary observing programs or projects, or provide support to complementary marine meteorological and oceanographic observing programs such as:

• The deployment of drifting buoys to support the Data Buoy Cooperation Panel to maintain a global array of buoys that measure: atmospheric pressure; air temperature; sea surface temperature; wind speed and wind direction; Lagrangian surface current; and
• The deployment of profiling floats to support the Argo Steering Team to establish a global array of floats that measure the temperature and salinity profiles in the upper 2000 m of the ocean.

The VOS Scheme is coordinated by the VOS Panel (VOSP), a sub-panel of the JCOMM Ship Observations Team (SOT).

The Terms of Reference of the VOSP are:

1. Review, recommend and coordinate the implementation of new and improved specialized shipboard meteorological instrumentation, siting and observing practices, as well as of associated software;
2. Support the development and maintenance of pilot projects such as VOSClim;
3. Develop and implement activities to enhance ship recruitment, including promotional brochures, training videos, etc; and
4. Prepare annually a report on the status of VOS operations, data availability and data quality.