Index of Help Pages
Frequently Asked Questions
The answers to some frequently asked questions about Global Wave Statistics Online can be found here.
Using the Web Site
The following pages describe the use of the Global Wave Statistics Online site. They are displayed as context sensitive help from the "Help" links on each page of the site.
- Selecting a geographic location.
- Confirming the location.
- Reviewing the data availability.
- Buying data for more than one area.
- Purchasing the area using WorldPay.
- The WorldPay Confirmation of Purchase.
- Choosing an analysis.
- Wind speed probability.
- Wave height and period scatter tables.
- Extreme wave heights.
- Persistence of storms and calms.
The data, and the NMIMET analysis used to create it
The data in Global Wave Statistics Online is based on visual observations of wind speed, wave height and direction made by ships of passage, and reported to the Main Marine Databank of the UK Meteorological Office.
The wave data has been quality controlled and quality enhanced by the well-validated NMIMET method. This method uses parametric modelling to improve the quality of the data, and in particular makes use of the far more numerous wind speed observations to improve the quality of the wave height statistics. The method does not use the visual estimates of wave period (which have been shown to be very inaccurate) but instead uses an analytical modelling of the joint probability distribution of heights and periods derived from instrumental data sets.
The analysis technique has been well-validated at a number of sites around the world, but may be expected to be most reliable in areas whose climate is dominated by wind driven seas. Whilst the NMIMET method takes account of swell, the wave period estimates may be expected to be less reliable in areas where swell is a major component of the climate (such as in tropical latitudes).
Areas prone to Typhoons or Hurricanes should also be treated with some caution. The wind speeds and wave heights associated with these events are unlikely to be fully represented in the visual observations due to the tendency of ships of passage to avoid them.
The following pages explain in more detail the way in which the data was generated and loaded into the database.
- The NMIMET Method of Analysis
- Wind Statistics
- Scatter Tables (Wave Height and Period)
- Extreme Wave Height Estimation
- Persistence of Storms and Calms
- Reliability and Validation
- European Database
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