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Observation components of the Global Observing System

Upper-air observationsMarine observationsAircraft
Satellite observationsOther observation platforms

Surface observations

The backbone of the surface-based sub-system continues to be about 11,000 stations (Volume A) on land making observations at or near the Earth’s surface, at least every three hours and often hourly, of meteorological parameters such as atmospheric pressure, wind speed and direction, air temperature and relative humidity.

Some 4000 of these stations comprise the Regional Basic Synoptic Networks (RBSNs) drawn up by the six WMO Regional Associations. Data from these stations are exchanged globally in real time. A subset of these surface stations are used in Global Climate Observing System (GCOS) Surface Network (GSN).
surface observations
Upper-air observations

From a network of roughly 900 upper-air stations, radiosondes, attached to free-rising balloons, make measurements of pressure, wind velocity, temperature and humidity from just above ground to heights of up to 30km. Over two thirds of the stations make observations at 0000UTC and 1200UTC. Between 100 and 200 stations make observations once per day. In ocean areas, radiosonde observations are taken by about 15 ships, which mainly ply the North Atlantic, fitted with automated shipboard upper-air sounding facilities (ASAP). A subset of upper-ait stations comprise the GCOS Upper-air Network (GUAN). For more details of the upper-air stations see the catalogue of upper air stations.

upper air observations


Marine observations

Over the oceans the GOS relies - in addition to satellites - on ships, moored and drifting buoys and stationary platforms. Observations made by ships recruited under the WMO Voluntary Observing Ship Programme, comprise much the same variables as at surface land stations with the important additions of sea surface temperature, wave height and period. The number of observing ships is about 7,000. About 40% are at sea at any given time. The operational drifting buoy programme comprised about 900 drifting buoys providing 12,000 sea surface temperature and surface air pressure reports per day. These ships and buoys are part of the WMO Marine Programme, which maintains lists of ships and observing standards.

marine observations








Aircraft observations

Over 3000 aircraft provide reports of pressure, winds and temperature during flight. The Aircraft Meteorological Data Relay (AMDAR) system makes high quality observations of winds and temperatures at cruising level as well as at selected levels in ascent and descent. The amount of data from aircraft has increased dramatically during recent years - from 78,000 reports in 2000 to almost 300,000 reports in 2005. Providing great potential for measurements in places where there is little or no radiosonde data, these systems are making a major contribution to the upper-air component of the GOS. See the WMO Aeronautical Programme for more on aviation meteorology.

aircraft observations


Satellite observations

The Environmental Observation Satellite network included five operational near-polar-orbiting satellites and six operational geostationary environmental observation satellites as well as several Research and Development satellites (Picture of satellite constellation). (See WMO's Space Programme for current information). Polar orbiting and geostationary satellites are normally equipped with visible and infra-red imagers and sounders, from which one can derive many meteorological parameters. Several of the polar-orbiting satellites are equipped with sounders instruments that can provide vertical profiles of temperature and humidity in cloud free areas. Geostationary satellites can be used to measure wind velocity in the tropics by tracking clouds and water vapour. Satellite sensors, communications and data assimilation techniques are evolving steadily so that better use is being made of the vast amount of satellite data. Improvements in numerical modelling in particular, have made it possible to develop increasingly sophisticated methods of deriving the temperature and humidity information directly from the satellite radiances. Research and Development (R&D) satellites comprise the newest constellation in the space-based component of the GOS. R&D missions provide valuable data for operational use as well as for many WMO supported programmes. Instruments on R&D missions either provide data not normally observed from operational meteorological satellites or improvements to current operational systems.


Other observation platforms

GOS also includes solar radiation observations, lightning detection, and tide-gauge measurements. In addition, wind-profiling and Doppler radars are proving to be extremely valuable in providing data of high resolution in both space and time, especially in the lower layers of the atmosphere. Wind profilers are especially useful in making observations at times between balloon-borne soundings, and have great potential as a part of integrated networks. Doppler radars are used extensively as part of national, and increasingly of regional networks, mainly for short range forecasting of severe weather phenomena. Particularly useful is the Doppler radar capability of making wind measurements and estimates of rainfall amounts.







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