Velocity Calibration of Doppler Current Profiler Transducers

Doppler current profilers are used in oceanography to measure oceanic circulation but also in hydrology to calculate the flow of rivers. They allow the retrieval of water mass profiles in terms of velocity and direction. Direction is obtained via an electronic compass and tilt sensors, while velocity is obtained by measuring Doppler pulse shifts back-scattered by particles located in water cells allocated along the instrument’s measurement range. Current meters are usually tested in towing basins or hydrodynamic channels, but these facilities present limits in terms of the measurement range, particles concentration and time costs. This paper presents a novel method developed to test the trueness of these velocity measurements in the laboratory, along with the uncertainty of this test and the results obtained with current meters and stand-alone profilers. The method is based on the measurement of the frequency of pulses emitted by each transducer of the instrument independently, and on the simulation of received echoes by a variable frequency sinusoidal signal.

The STIMTEC experiment at the Reiche Zeche ULab

<p><span>Between early 2018 and late 2019 the STIMTEC hydraulic stimulation experiment was performed at ca.~130 m below surface at the Reiche Zeche research mine in Freiberg, Saxony/Germany. The project aims at gaining insight into the creation and growth of fractures in anisotropic and heterogeneous crystalline rock units, to develop and optimise hydraulic stimulation techniques and to control the associated induced seismicity under in situ conditions at the mine-scale. These aspects of failure and associated seismicity are important for the development of enhanced geothermal energy systems. We present the infrastructure developed for the STIMTEC experiment and provide an overview of the obtained data, including 295 m of core material retrieved from 17 boreholes, 225 m of acoustic TV log, >50 TB of continuous passive seismic data from four field stimulation and hydraulic testing campaigns, as well as ~300 active velocity calibration measurements. </span></p><p><span>W</span><span>e highlight some of the first results regarding the hydro-mechanical and seismic response to the stimulation, the rock mass characterisation in-situ and in the laboratory, as well as 3-D numerical modelling of the stress state and fracturing. The heterogeneity and anisotropy of the strongly foliated metamorphic gneiss significantly affects fracture creation and propagation </span><span>in the experiment.</span></p>

Searching for g modes

Context. The recent claims of g-mode detection have restarted the search for these potentially extremely important modes. These claims can be reassessed in view of the different data sets available from the SoHO instruments and ground-based instruments. Aims. We produce a new calibration of the GOLF data with a more consistent p-mode amplitude and a more consistent time shift correction compared to the time series used in the past. Methods. The calibration of 22 yr of GOLF data is done with a simpler approach that uses only the predictive radial velocity of the SoHO spacecraft as a reference. Using p modes, we measure and correct the time shift between ground- and space-based instruments and the GOLF instrument. Results. The p-mode velocity calibration is now consistent to within a few percent with other instruments. The remaining time shifts are within ±5 s for 99.8% of the time series.

CALIBRATION OF A DRAG TILT CURRENT VELOCIMETER FOR AN OPEN CHANNEL APPLICATION

Water is one of the prime elements responsible for life on earth with two thirds of the earth's surface covered by it. Managing water resources effectively can promote conservation and make the best use of our limited water resources. Having knowledge about flow information on the river networks can be very beneficial for applications such as hydropower, transportation, irrigation, flood mitigation, water treatment, industrial and domestic needs. The development of simple and inexpensive instrument (<RM500) is to help researchers to produce and measure flows on spatial river at a very low cost. The analytic approximation was derived for giving relationship of the instrument’s tilting behavior on water velocity. Calibration process was held and the data are used to investigate the relationship between the measurement collected from the experiment and the known values. Analyzing the experiment results, it was concluded that the instrument tilting in response to the water velocities but not up to the expected known values. Random and systematic errors arise during calibration processes which contribute to the high uncertainties of the instrument. The documented experiments, procedure and facility used for the calibration are given in this paper. It is shown that the accuracy relationship of this instrument against the analytic approximation identified is 66.45%.