Wave height from pressure measurements

Abstract

For this project, Environment Mapping & Surveying (EMS) from South Africa has provided two pressure meters for wave measuring. These pressure meters give a value for the pressure, which must be converted to pressure and after that to a Rayleigh distribution and a wave spectrum. Therefore is the purpose of this report to test the pressure meter and to convert the outcomes of the pressure meter to wave heights, resulting in a Rayleigh distribution and a wave spectrum. At first, there were calibration tests in still water to measure the hydrostatic pressure. The pressure meter was lowered in the water, with some stops, hanging still. At that moment the water depth could be found in the graph of the measured values in the time, so the relation between the water depth and the measured values is found. With that relation it is possible to find the relation between the measured values and the real pressure. After this, the verification tests are done. These tests are done in the Delta Flume of Deltares, during the Bardex II project. The pressure meter was lowered into the flume, to measure the waves that were made for the Bardex II project. After this, the outcomes were converted by three Matlab-scripts into a Rayleigh distribution, a wave spectrum and some characteristic values, like Hs and Hm0. These figures and the values are compared to the measurements of Deltares to find the accuracy of the pressure meter. The comparison with the measurements of Deltares shows that the pressure meter has an accuracy of five percent. The most important characteristic values are even more accurate, up to one or two percent. The figures of the Rayleigh distribution and the wave spectrum are comparable to the figures of Deltares. These outcomes make the pressure meter a quite accurate instrument to measure waves. Due to the fact that this instrument is inexpensive in comparison to other wave meters, it is a very usable instrument for fieldwork or low-budget projects.