Underwater Measurement System Research Articles

Three dimensional reconstruction and measurement of underwater spent fuel assemblies

It is an important work to measure the dimensions of underwater spent fuel assemblies in the nuclear power industry during the overhaul, to judging whether the spent fuel assemblies can continue to be used. In this paper, a three dimensional reconstruction method for underwater spent fuel assemblies of nuclear reactor based on linear structured light is proposed, and the topography and size measurement was carried out based on the reconstructed 3D model. Multiple linear structured light sensors are used to obtain contour size data, and the shape data of the whole spent fuel assembly can be collected by one-dimensional scanning motion. In this paper, we also presented a corrected model to correct the measurement error introduced by lead-glass and water is corrected. Then, we set up an underwater measurement system for spent fuel assembly based on this method. Finally, an underwater measurement experiment is carried out to verify the 3D reconstruction ability and measurement ability of the system, and the measurement error is less than ±0.05 mm.

Fluorescence for non-contact detection of living salmon lice on salmon skin

This work presents a promising method for automatic, non-contact, detection and counting of salmon lice infested on salmon in an aquacultural farm setting. The method uses fluorescence from chitin in the visual part of spectrum to enhance the contrast between fish skin and salmon lice, and show that the fluorescence is even strong enough to give a real-time view of the digestive and reproduction system in live lice without use of staining dyes. The wavelengths used are compatible with an underwater measurement system.

Fluorescence for non-contact detection of salmon lice in fish farms

This work presents a promising method for automatic non-contact detection and counting of salmon lice infested on salmon in an aquacultural farm setting. The method uses fluorescence in the visual part of spectrum to enhance the contrast between fish skin and lice. The wavelengths used are compatible with an underwater measurement system.

Analysing the Impact on Underwater Noise of Changes to the Parameters of a Ship’s Machinery

Abstract A ship moving over the surface of water generates disturbances that are perceived as noise, both in the air and under water. Due to its density, water is an excellent medium for transmitting acoustic waves over long distances. This article describes the impact of the settings of a ship’s machinery on the nature of the generated noise. Our analysis includes the frequency characteristics of the noise generated by the moving ship. Data were obtained using an underwater measurement system, and the measured objects were two ships moving on specific trajectories with certain machinery settings. The acquired data were analysed in the frequency domain to explore the possibilities of the acoustic classification of ships and diagnostics of source mechanisms.

Detection of Floating Objects Based on Hydroacoustic and Hydrodynamic Pressure Measurements in the Coastal Zone

Abstract The development of coastal infrastructure and related maritime transport necessitatesthe intensification of vessel traffic monitoring. Navigation systems used in this research are traditionally based on the information transmitted by radio waves. Marine traffic safety requires constant supervision carried out by dedicated systems, the operation of which may be limitedby difficult environmental conditions. The possibilities of supporting navigation systems with underwater observation systems are explored here. The research was carried out using an underwater measurement system. Local disturbances of the hydroacoustic and hydrodynamic field from the moving vessels were analysed. The potential for identifying a moving vessel, for example for offshore infrastructure security purposes, is demonstrated.

Depth dependence of pile driving noise measured at the research platform FINO3

Impact pile driving is a source of high-amplitude underwater sound that can propagate large distances and may have a negative impact on marine fauna. In Germany, wind farm operators are required to monitor underwater sound levels and to ensure that the levels do not exceed certain values. Mainly because of practical reasons sound measurements are usually performed with hydrophones about 2 to 3 m above the sea-floor. It is of some interest to know whether these sound values are representative for the entire water column. We investigated this with an underwater measurement system that was designed to provide simultaneous sound measurements at up to eight different heights above the sea-floor. It consisted of a bottom mounted tripod to which a vertical chain of five to six hydrophones was attached with the top-most hydrophone being located about four meters below the sea-surface. The system was cable-connected to the research platform FINO3. This paper analyses the depth dependence of pile driving noise that was emitted from piling operations in the nearby offshore wind-farm DanTysk with propagating distances between pile and FINO3 ranging between 3km and 15km. Observed sound exposure levels (SEL) were usually somewhat larger at 2 m above the sea-floor than at hydrophones higher in the water column. Details about the variability and frequency dependence of the observed differences are presented.

Underwater radiated noise of the NOAA ship Oscar Dyson

The NOAA Ship OSCAR DYSON is the First-in-Class fisheries research vessel designed and built for the National Oceanic and Atmospheric Administration (NOAA) for fish stock assessment. One of its most important contractual requirements was to achieve an underwater noise limit established by the International Council for the Exploration of the Seas (ICES). The underwater noise limit has been specified by ICES over too large a frequency range and too small a resolution to allow for measurements with commercial grade test equipment. Modifications to the limit were made by NOAA which allowed the authors to develop a simple, deployable underwater measurement system. This system was then used to measure underwater noise from the OSCAR DYSON during sea trials in the Gulf of Mexico. The system consisted of a hydrophone array, signal conditioning and data acquisition hardware. The distance between the hydrophone array and the vessel must also be measured during the survey with the vessel in the acoustic far-field. Results from the far-field noise measurements were compiled and then compared to the ICES specification requirements. Self-noise from permanently mounted hydrophones in the hull were also measured during the survey. Finally, a comparison between the commercial system used by the authors and subsequent measurements performed by the U.S. Navy at their acoustic underwater test facility is made. These show good agreement at all but the lowest frequencies.

Measurement of underwater noise of the new National Oceanic and Atmospheric Administration (NOAA) Ship OSCAR DYSON

The NOAA Ship OSCAR DYSON is the first‐in‐class fisheries research vessel (FRV) designed and built for National Oceanic and Atmospheric Administration (NOAA) for fish stock assessment. One of its most important contractual requirements was to meet the underwater noise limit of 1995 International Council for the Exploration of the Seas (ICES) report. This paper describes the efforts to conduct the underwater noise tests of the vessel. A commercial underwater measurement system was developed which was set‐up off the Gulf of Mexico. The system consists of a small hydrophone array, signal conditioning, and data acquisition hardware. Field calibration was performed. Requirements for mounting the hydrophones and operation of a support vessel are discussed. In addition to measuring underwater sound, the distance between the source and receiver was also measured. Results are compared to the specification requirements and subsequent measurements performed by the U.S. Navy.

Arrival time determined by vertical array: Experimental results in shallow water

The arrival time determined by vertical array is a useful parameter to apply matched field processing (MFP) methods for source localization. In this paper, the procedure including wavelet transform for extracting the signal, adaptive filter for retrieving the signal, and wigner-vill distribution for determining the arrival time between sensors is presented. During the South China Sea ASIAEX Experiment, the 103 m deep source was towed by a ship. The data receiving system was a satellite–buoy underwater measurement system with a 16-element vertical line array. The experiment showed that the data was collected with very good quality. Results of this procedure are more efficient, and faster than earlier results based on power spectrum for MFP.

A nearfield, underwater measurement system

A nearfield acoustic measurement technique for accurately computing the farfield radiation characteristics of underwater sound transducers was developed, implemented, and evaluated. The analysis was based on evaluation of a form of the Helmholtz integral which utilizes a Green’s function that vanished over the surface of integration, thereby requiring only knowledge of the nearfield acoustic pressure for computing the farfield radiation. An experimental program was conducted to evaluate the technique. Details of the nearfield measurement instrumentation are presented. Comparisons between conventionally measured farfield properties of four different types of test transducers and the results obtained by using the nearfield technique are given. The results showed that excellent agreement was achieved for the radiation properties compared. For the directional responses, the nearfield technique matched the conventionally measured results over the minor lobe structure as well as over the major lobe structure of the pattern. The results also showed that absolute sound-pressure levels could be determined accurately and with relative ease.

A nearfield, underwater measurement system

A nearfield acoustic measurement technique for accurately computing the farfield radiation characteristics of underwater sound transducers was developed, implemented, and evaluated. The analysis was based on evaluation of a form of the Helmholtz integral which utilizes a Green's function that vanished over the surface of integration, thereby requiring only knowledge of the nearfield acoustic pressure for computing the farfield radiation. An experimental program was conducted to provide corroboration of the technique. Details of the automated, digital, nearfield measurement instrumentation are presented. Comparisons between conventionally measured farfield properties of four different types of test transducers and the results obtained by using the nearfield technique are given. The results showed that excellent agreement was achieved for the radiation properties compared. For the directional responses, the nearfield technique matched the conventionally measured results over the minor lobe structure as well as over the major lobe structure of the pattern. The results also showed that absolute sound pressure levels and directivity indices could be ascertained accurately and with relative ease. [Work supported by NAVSEA 034.]