Manual on sea level measurement and ... - unesdoc - Unesco

Sea Level Measurement and InterpretationComparison of Radar Devices in GermanyChristoph J Blasi and Ulrich BarjenbruchFederal Institute of Hydrology (BfG), D-56002 Koblenz, Germany,E-mail: blasi@bafg.deNearly all kinds of engineering in coastal area rely onthe available information on water level. The classicalway of reading the water level is by a staff gauge anda float. These measuring systems were used for a verylong time and were upgraded in various ways to storethe recorded data.In the late 1990s, radar devices, which were mainlyused in process technology, were introduced intohydrometry. The Federal Institute of Hydrology (BfG)made the first investigation at the beginning of 2000(BfG 2002). As technology of these devices developed,additional tests were made. These tests were part of aresearch project with the aim of finding the core foundationfor measurements of waves, sea state, waterlevel and thickness of ice. The results are quite reasonableand available via http://www.bafg.de/servlet/is/7833/. One of the main parts of the project was themeasurement of waves in a broader sense. Therefore alot of attention was paid to the theory of detection andmeasurement of water level as a part of waves underdifferent conditions. Different tests were undertakenunder both laboratory and field conditions to accessthe influence of the measurement.The aim of this paper is to show the results from thefield test, with a view to giving the reader help andsupport in choosing the right radar gauge to measurewater level. However, the physical background and theapplication of radar in distance measurement will notbe discussed here. The reader may refer to the report ofthe research project available from the authors [pleasecite the source]. As mentioned before, there were testsin the hydraulic laboratory and as well in the field.During the laboratory test, the backscatter from differentradar devices for various wave types and watersurfaces were investigated to determine the suitabilityfor wave and water-level measurement.With this information, four different devices werechosen for the field test. The field test was at thegauging station on Borkum Südstrand, which is onthe island of Borkum and very close to the border withThe Netherlands. This location has all the requiredconditions, such as tidal range, different types of wave,sea state, changes of salinity, rough seas, saline airand annual temperature variation. Furthermore, theBorkum Südstrand Gauging Station is an official gaugeof the Water and Shipping Way Authority. The gaugeand the setting up of the radar sensors are shown inFigure 1.The devices themselves are described as Rad_A up toRad_D. This was done under an agreement with themanufacturers. If detailed information is required, thereader may contact the author. For establishing thereference for the four radar sensors and the officialgauge, a calibrated Magnetostrictive-Sensor (a specialkind of float gauge without a stilling well) was used.Most of the radar gauges work on the same principle.Figure 1. The Borkum Südstrand Gauging Station and installation of the of the radar gauges and the localreference.IOC <strong>Manual</strong>s and Guides No 14 vol IV65