Wir untersuchen sowohl einzelne Prozesse in aquatischen Systemen als auch ganze Systeme natürlicher Gewässer. Neben der Grundlagenforschung und der interdisziplinären Systemanalyse stehen anwendungsnahe Projekte besonders im Fokus.
High-Resolution Measurements of Turbulent Flow Close to the Sediment–Water Interface Using a Bistatic Acoustic Profiler
Velocity profile measurements at high spatial and temporal resolution are required for the detailed study of solute and momentum transfer close to the sediment–water interface. Still, not many devices allow such measurements in natural systems. Recently, a bistatic acoustic current profiler has become commercially available that allows the recording of profiles at down to 1-mm resolution with a maximum frequency of 100 Hz and a profile length of 3.5 cm. This study tested the ability to characterize the turbulent flow of this profiler in a laboratory flume and in a run of the river reservoir. The tests showed that average velocities were reliably measured in the upper 2.5 cm, while the flow statistics were affected by Doppler noise and signal decorrelation. The latter is caused by the decreasing overlap between the individual beam signals. Doppler noise can be estimated and accounted for by established correction procedures, but currently there is no method to quantify the influence of signal decorrelation. Both error sources mainly affect the measured variances of the velocities, while the Reynolds stresses are reliable as long as there is no interference with the solid bottom. In the field application, most problems arise because of the necessity of coordinate system rotation, since a perfect alignment of the profiler with the current is not possible. Also, because of the coordinate system rotation, the Reynolds stresses become contaminated by noise, which can be removed by low-pass filtering. Still, this filtering results in loss of the turbulent signal, which was estimated in this study to be between 2% and 10%.
Brand,A.; Noss,C.; Dinkel,C.; Holzner,M. (2016) High-Resolution Measurements of Turbulent Flow Close to the Sediment–Water Interface Using a Bistatic Acoustic Profiler, Journal of Atmospheric and Oceanic Technology, 33(4), 769-788, doi:10.1175/JTECH-D-15-0152.1, Institutional Repository
A new robust oxygen-temperature sensor for aquatic eddy covariance measurements
The fragility of thin Clark-type glass microelectrodes used in aquatic eddy covariance measurements of benthic oxygen fluxes is a challenge when using this powerful technique. This study presents a new fast-responding dual oxygen-temperature sensor for eddy covariance measurements that is far more robust. Response time tests in the lab, where the sensor was inserted from air into water, revealed 90% response times of 0.51 s and 0.34 s for oxygen and temperature measurements, respectively. In wave tank tests, the new sensor showed no stirring sensitivity in contrast to Clark-type microelectrodes. Other tests in a flume and in a particle-free water tank revealed how close the sensor can be positioned to the measuring volume of the Acoustic Doppler Velocimeter without disturbing velocity recordings. In field tests at river sites, all > 24 h, the new sensor recorded high-quality eddy covariance data for the entire deployment. Similar positive results were obtained in deployments at a marine site with unidirectional current flow overlaid with minor wave action. Concurrently deployed eddy covariance systems based on the new sensor and a traditional Clark-type microelectrode revealed that they recorded statistically equivalent fluxes and similar velocity-oxygen cospectra until the microelectrode broke after 2 h. The significant increase in robustness of the new sensor was achieved by relying on a larger sensor tip. This put some constrains on how the sensor should be deployed and fluxes extracted, but given the substantial gain in performance, it is a viable alternative for eddy covariance measurements in many aquatic environments.
Der faszinierende Kivusee und das gelöste Methan in seinem Tiefenwasser könnten eine ganze Forschungsanstalt auf Trab halten. Mit unseren Forschungsprojekten versuchen wir, Grundlagen für eine nachhaltige und sichere Nutzung des Methans zu schaffen.
Abwasser ist mit antibiotikaresistenten Bakterien belastet.
Wir untersuchen ihre Ausbreitung in die Umwelt und Gegenmassnahmen.
Seen sind grosse Wärmespeicher. Inwiefern kann diese Wärme genutzt werden, um den Verbrauch von Brennstoffen und Elektrizität zum Heizen oder Kühlen zu vermindern?