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parameters. Although considerable progress has been achieved due to the use of remote 
sensing systems such as satellites, in-situ data recording still is indispensable for the analyses 
on which model computations are based. However, the availability of direct observations and 
measurements, in terms of density and distribution, still is not satisfactory, particularly in view 
of the fact that over two thirds of the surface of the Earth is covered by water. It should be 
noted that as the length of the prediction period increases, the influence of parameters in the 
near-surface water masses is growing in importance. 
With respect to applications of the numerical prediction models - particularly marine weather 
forecasts and warnings - in-situ measuring data from the open ocean and from the coastal 
areas, with adequate temporal and spatial coverage, still are indispensable. 
In climate monitoring and in the investigation of climate changes and trends etc, homogeneous 
data material is required that has been collected over long periods of time using identical or 
comparable methods and techniques. Especially with respect to marine climatological 
applications, the traditional system of voluntary observing merchant ships has provided a 
wealth of information dating back as far as the beginning of the 19 th century. Although climate 
process studies, climate development scenarios or assessments of the impacts of climate 
changes today are based largely on model computations, model verification by means of 
suitable observation data still is indispensable. 
To calibrate and validate satellite data, reliable direct measurements are still needed for 
comparison. They must be measured in the ocean areas concerned during the same periods of 
time. 
Expert opinions, information and consultative services rely particularly on in-situ 
measurements and observation data. When reconstructing, for example, the marine 
meteorological situation at a particular position and time, such data are indispensable. That 
applies also to computations of, e.g., the load parameters for marine structures, for which 
homogeneous data material collected during many years is absolutely essential. 
Monitoring methods and systems 
A number of operational systems complementing one another have been established for real 
time recording of maritime in-situ observation and measuring data. 
Voluntary Observing Ships (VOS) 
The Voluntary Observing Ships Scheme of the World Meteorological Organization (WMO) is 
of paramount importance. Over 40 seafaring nations participate in an observation network of 
vessels which, generally on a voluntary basis and free of charge, are making weather 
observations and measurements on the basis of a uniform standard. The WMO is in charge of 
co-ordination. In accordance with an international convention, numerous marine 
meteorological and associated oceanographic variables are recorded every six hours at agreed 
Universal Time intervals. The variables include, e.g. wind direction and speed, visibility, 
weather conditions, air pressure, air and water temperature, clouds, waves etc. The observing 
ships are recruited by the meteorological port service which also provides the required 
instruments, equipment and logbooks and trains the ships 1 crews in the observation 
techniques. Port services of DWD exist in all German sea ports. 
DWD also deploys automatic stations on a number of Voluntary Observing Ships, where the 
nautical personnel only enters those values manually that cannot be recorded automatically. 
Part of the data are distributed world-wide in real-time via the meteorological communication