Author(s): Ivo Wenneker; Niels Jacobsen
Keywords: Field measurements; Water level; Waves
Abstract: Field measurements at sea or lakes of water levels and waves yield data for practical and research purposes. For example, they provide operational data for ship navigation and storm surge prediction. Furthermore, field measurement data can be used for numerical models (either to feed operational models or for model calibration and validation) .In such and other applications, field measurement data are (after suitable checks and validation) often assumed to be the‘absolute truth’. This implies that daily operational decisions or numerical model input data are based on field measurement data without questioning the accuracy of this data (because of the checks and validation) .We present two case studies relating to practical situations: water level measurements from measurement poles, and wave measurements in the wave breaking zone. These case studies were carried out by comparing data sets obtained by‘redundant measurements’, i. e. measurements of some physical parameter at the same location by more than one instrument. The most important conclusion is that, even when the‘redundant’data sets are close to each other in‘mild’conditions (thus verifying that both instruments are calibrated and installed correctly) ,under more‘extreme’conditions (e. g. storms and large (tidal) current velocities) significant deviations between the data sets can exist. This implies that at least one of the data sets deviates from the‘absolute truth’. The deviations can be attributed to various aspects of the measurement configuration (the instrument itself and properties of the measurement technique; interaction between hydrodynamics (waves and currents) and the measurement pole and/or instrument suspension; data processing) .