The NMIMET Analysis

The data retrieved from the Marine Databank was subjected to the NMIMET quality enhancing analysis and checking procedures before being passed to a plotter for generation of the pages of data presented in the book 'Global Wave Statistics'. At the same time the NMIMET fitted coefficients and other important data attributes were stored in a database for Global Wave Statistics Online.

The software used for this purpose was a specially adapted version of the NMIMET program. The special features of the adapted program were mainly concerned with the additional 'housekeeping' and quality control operations needed for checking the very large quantities of data and organizing them into the correct sequence. There were also some minor differences in the actual analysis method and resulting output.

A detailed account of the analysis method, including the differences from the original NMIMET method, is given in Appendix_A3. Later pages on 'Reliability and Validation' describe the special quality control procedures developed to compile the database and indicates the reliability of the analysis techniques. The NMIMET analysis methods have been developed for deriving wave data of enhanced reliability from visual observations of waves and winds, and are based on use of parametric models of relevant statistical relationships as described in detail in [24] - [27].

Two such models are used, the first being of the joint frequency distribution or scatter diagram of wave heights and wind speeds used for deriving enhanced wave height statistics. The second is of the joint frequency distribution of wave heights and periods, which are synthesized from the enhanced wave height statistics without any use of visual observations of period (which are known to be very unreliable).