FASTEX Central Archive Buoy Quality Controls

Data uniqueness:

For a few buoys, data came both from GPC (Argos Global Processing Centres : Toulouse and Landover) and LUT (ground stations named 'Local User Terminals'). For each of these buoys, the data set coming from the LUT was compared to the GPC data set, and the redundancy of the LUT one allowed to removed it (only data coming from the GPC were keeped).

Visual examination

For each buoy, the temporal evolution of available parameters was plotted and visually examined. It allowed to show:
1. unrealistic peaks in latitude, longitude and pressure; these data were set to 'bad'
2. buoys ashore: sst data were removed and the documentation updated

Gross limit checks

After several attemps to improve 'limit values' for the domain of interest, it appeared that real time gross limits could be improved only for pressure (severe weather conditions are frequent for some buoys according to their positions, more frequent than, for example, for ships - which try to avoid them; following that, the range of values is quite wide).
For each doubtful pressure observation (below 940 or above 1040), data were visually examined and compared to neighbouring observations (in space and time). If a problem appeared, the wrong value was flagged; some of them were corrected, see the data correction section for more details.

Controls on pressure

Each pressure measurement was compared to 'neighbouring' observations from ships or buoys (i.e. a 500 km square over a 12 hour interval, centered on the point which is controlled; this area might be extended when a few observations are available, or reduced for a great number of observations). When the difference between the pressure value and the average of the neighbouring observations was greater than a value set to 12hPa, data were checked with the use, in some cases, of the sea level pressure field from the ARPEGE analysis.

After that, for each buoy, the temporal evolution of pressure was compared to limit values depending on the time between the two measurements;

temporal interval	limit on pressure tendency	limit on temperature tendency
less than 1 hour	4 hPa	4 degrees C
1 hour	6 hPa	6 degrees C
3 hours	13 hPa	8 degrees C
6 hours	20 hPa	12 degrees C
12 hours	30 hPa	15 degrees C
24 hours	40 hPa	18 degrees C

A third check was also applied, using the pressure tendency. When, for a buoy, the time between two pressure observations was equal to 3hours, and when the pressure tendency was available (allowing the computation of the first pressure using the second pressure and the tendency), the difference between the first value (from the message) and the calculated value was computed. If the difference was greater than 3hPa per 6 hours, pressure was visually checked.

Controls on temperature

For each buoy, the temporal evolution of the temperature was calculated and compared to the limit values given in the previous table. But this control didn't allow to flag data as being 'bad'.

Data correction

Pressure data

In the following cases, and only in these cases and when the error is obvious, the decision was taken to correct pressure values:

controls used to show up errors	parameters used to correct data
peaks in the pressure temporal evolution and/or gross limit checks and/or comparison with neighbouring observations and/or temporal evolution of pressure for this buoy and/or use of the buoy pressure tendency and/or comparison with the closer sea surface pressure map (over Atlantic)	neighbouring pressures from other buoys or ships when available and previous/next pressure values of the same buoy (if not too far) and pressure tendency when available




Flagging/correcting data

When a correction is made, the corresponding flag is set to 8 (corrected value).
When the correction is not obvious, but the value obviously suspect or bad, flags were used to improve the data qualification (set to 6 or 7).

Summary