A peak in the total number of VOS was reached in 1984/85,
when 7,700 ships worldwide were listed as participating in the VOS
Scheme. Since then, there has been an irregular but noticeable decline.
In December 2004, there were some 6,500 ships listed at WMO as observing
ships from 53 countries and by mid-2005 there were fewer than 6,000
ships. However, analysis of ships’ weather reports show that
the number of VOS that are actively reporting is actually far less.
Based on the first six months of 2005, there were approximately 3,025
ships worldwide reporting pressure, and only 2,652 reporting sea surface
temperature. It is recognized that priority must often be given to
other navigational duties, particularly in areas of dense shipping,
and that there will be periods when a ship is in port or dry-dock
and when it will not be possible to perform weather observations.
However, the number of actively participating ships is clearly in
a decline and needs to be reversed.
As might be expected, real-time reports from the VOS are
heavily concentrated along the major shipping routes, primarily in
the North Atlantic and North Pacific Oceans. The attached chart shows
details of the geographical distribution of ships weather reports
for December 2006, and the most striking feature is the large data-void
areas in all southern hemisphere oceans. While this situation certainly
reflects the relatively small numbers of ships sailing in these waters,
it also makes it more essential that ships sailing in these areas
actively participate in the VOS, thus contributing to the global observing
programme and the consequent enhancement of the forecast and warning
services to the mariner.
Of course, as the VOS reports are part of a global data
capture programme, these reports are of value from all the oceans
and seas of the world, and even the relatively well-frequented North
Atlantic and North Pacific Oceans require more observational data.