Freshwater and saltwater experiments were completed to determine the magnetic difference generated by the difference in conductivity. Wave parameters of 4-m-long waves with a 0.56-Hz frequency and a 0.1-m amplitude were used in this experiment. Accelerometer measurements and local gradients were used to identify magnetic noise produced from tank vibrations. This technique significantly reduced the extraneous magnetic distortions that were detected simultaneously by both sensors and additionally doubled the magnetic signal of surface waves. A laboratory experiment was conducted at the Surge Structure Atmosphere Interaction (SUSTAIN) facility to measure the magnetic signature of surface waves using a differential method: a pair of magnetometers, separated horizontally by one-half wavelength, were placed at several locations on the outer tank walls. The green line is the effect of magnetic permeability.Ī magnetic signature is created by secondary magnetic field fluctuations caused by the phenomenon of seawater moving in Earth’s magnetic field. The blue curve represents the traditional theoretical curve ( Weaver 1965 Lilley et al. The pink line shows the 95% confidence intervals of those averaged points. More information regarding signal strength can be found in the geometrics manual ( Geometrics 2015). Signal strength is determined to be high if the quality is >2 and otherwise deemed low. The red circle indicates positions with low signal strength. The blue circles show the surveys averaged in locations with high signal strength. The blue and red symbols indicate the averaged magnetic amplitude from all surveys conducted for that experiment type (saltwater, freshwater, or empty tank). The averaged magnetic signature amplitude at the tank bottom, near the air–water interface, at the tank top, and 2.5 m above the tank top for (a) saltwater and (b) freshwater and (c) when the tank was empty. ![]() The green line shows the difference between the master and slave signals. The red line is the magnetic signature from the master magnetometer, and the blue line is the signal from the slave magnetometer. Time series of the magnetometer data after filtering out magnetic noise and normalization. The dashed lines indicate 95% confidence intervals of the spectrum. The magnetometer data are shown in red, and the magnetic noise is shown in blue. Spectra of the master magnetometer data and the magnetic noise calculated from displacement of the accelerometer attached near the magnetometer filtered over the range of 0.2 to 1 Hz. The dashed lines indicate 95% confidence intervals. Spectra calculated from the magnetic signature of surface waves. (d) Wave measurements over the same time as the magnetic data shown in (c). (c) The extended version of the magnetic time series shown in (a). (b) The three ultrasonic distance measures are represented by red, blue, and black, which show the wave elevation. The master (red) and slave (blue) signals. (a) Time series subset of magnetic signature of surface waves. (b) View of the tank from below with transparency to see the wave recorder. Multiple surveys were conducted at each survey location. ![]() The numbering indicates the positions of the magnetometer pair for each survey. For each survey, red indicates the position of the master magnetometer, and green indicates the location of the slave magnetometer. Schematic diagram of the laboratory experiment ( Kluge et al. (b) TW Connectivity 4630A low-noise triaxial accelerometer. (a) Sensor, sensor cable, and sensor driver module and active zone for the cesium-vapor magnetometer. Instrumentation used in the laboratory experiment at the SUSTAIN facility. University of Miami Rosenstiel School of Marine and Atmospheric Science (RSMAS) Surge Structure Atmosphere Interaction tank.
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