Quality Control of GSN Data

(The material below has been extracted from the Manual on the GDPS (Reproduced from Annex C, Report of the Second Joint CCl/CBS Meeting on the GCOS Surface Network, De Bilt, The Netherlands, 25-27 June, 1997))

This page describes some of the practices used in collecting and assessing the quality of surface meteorological data from the GCOS Surface Network (GSN). Other techniques are described on the page describing observing requirements for the GSN. See also the Guide to the GCOS Surface and Upper-Air Networks: GSN and GUAN (Version 1.1) GCOS-73

WMO-No. 485, Attachment II.14

Quality Of Observational Data

20. Centers with global, hemispheric or near-hemispheric models should monitor the quality of one or more of the main types of observations using techniques such as those listed in Table E. Statistics should be compiled separately for each land station by station index number, for each ship or aircraft by call sign, for each buoy by identifier, and for each satellite by identifier, and for various geographic areas and levels in the atmosphere.

21. The centers should analyze the results and produce in an agreed format lists of observations believed to be consistently of low quality, together with information on which element of the observation (pressure, temperature, etc.) is thought to be of low quality and the evidence for considering it as such. These lists should be based on data received over one month and should be exchanged monthly between participating centers.

22. For each type of observation a lead centre shall be nominated from time to time by the president of CBS. The lead centre should liaise with the participating centers to coordinate all the monitoring results of that observation type and to define common methods and criteria to be used for compiling the monthly statistics. The lead centre should draw the attention of appropriate focal points where they have been identified and of the WMO Secretariat to obvious problems as they are detected. It should also produce every six months a consolidated list of observations of the relevant observation type believed to be of consistently low quality. Information on problems with observing systems, as well as individual observations, should also be included. When compiling the consolidated lists of suspect stations the lead centers should be rigorous so as to identify only those stations where they are confident that the observations are of consistently low quality. They should state which elements of the observation are considered of low quality and provide as much information as possible identifying the problem. The list should be passed on to the participating centers and to the WMO Secretariat. Where focal points have not been identified the Secretariat should notify Members of agencies responsible for the observations which appear to be of low quality, and request them to make an investigation with a view to identifying and correcting any possible cause of error. Members should be asked to reply within a fixed period of time, reporting on any remedial action and stating if any assistance is required. Monitoring results including follow-up action should be made available to CBS, the Executive Council and Congress. In the case of enquiries made by WMO, feedback to the lead centers is requested.

Attachment II.14

Table E  -  Techniques for monitoring the quality of observations

1. Compilation of statistics on the difference between observed values and the analysis and first-guess field;

2. Compilation of statistics on observations which fail the routine quality-control checks;

3. Examination of time series of observations from a particular station (particularly useful in data-sparse areas);

4. Compilation of statistics on the differences between reported values of geopotential height and geopotential height recalculated from significant level data for radiosonde stations, using common formulae for all stations;

5. For surface stations which report both mean sea-level pressure and station-level pressure, compilation of statistics on differences between reported mean sea-level pressure and mean sea-level pressure recomputed from reported station-level pressure and temperature and published values of station elevation;

6. Compilation of co-location statistics.