Measurement errors of instruments for velocity, wave heigt, sand concentration and bed levels in field conditions

Abstract

Field measurements of hydrodynamics (fluid velocities and wave height), sediment dynamics (sand concentrations) and morphodynamics (bar behaviour) as performed during the COAST3D campaigns at the Egmond site in 1998 and at the Teignmouth site in 1999 inevitably involve the problem of the accuracy of the measured variables. The measurement errors are related to: • the physical size of the instrument including supports, cables, housing for electronics, etc.; • the measurement principle including electronic instability, drift, offset, calibration procedure, sampling size and applicability and validity ranges of the instrument concerned; • the conversion principle including assumptions of applied theories (for example: conversion from fluid pressure to wave height; errors in position of pressure sensor above bed). Information of the measurement errors involved can be obtained by comparing instruments based on different measurement principles under controlled conditions. Recently several studies focussing on hydrodynamics and sand transport in the large scale wave tanks of Delft Hydraulics (The Netherlands) and of the ‘Forschungszentrum Küste’ in Hannover (Germany) have been carried out. Various types of instruments have been used to measure fluid velocities, wave heights and sand concentrations during the experiments in the wave tanks. In addition data sets from various field experiments are used to evaluate the performance of the instruments considered. In this note some results of instrument intercomparisons are presented. Furthermore, information of instrument characteristics are given.