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Before using observations for verification, care has to be taken to process the data to remove any erroneous observations. Moreover, extra care has to be taken to match the scale of both model and observations. This scale matching is achieved by averaging the hourly data in ±1 hour time windows centered on the four major synoptic times corresponding to the normal model output times. The original quality control and averaging procedure was discussed in Bidlot et al. (2002). It was extended to include platform data as described in Sætra and Bidlot (2004).
Match-up between observations and the model data
The interpolation method for deriving forecast values at the observation location for the ocean waves is called the inverse-distance-weighting interpolation (IDWI). The interpolated value is determined by the weighted average of the values of those of four neighbour points which hold valid values.
The weight function follows:
w = 1/d²,
with d the distance between forecast and observation locations.
Scatter index
The scatter index is a measure of the size of the deviation of forecasts from observations relative to the magnitude of the observations. A smaller scatter index value means better forecasts.
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