This paper presents the results of hydroacoustic noise research in three large European rivers: the Danube, the Sava, and the Tisa. Noise in these rivers was observed during a period of ten years, which includes all annual variation in hydrological and meteorological conditions (flow rate, speed of flow, wind speed, etc.). Noise spectra are characterized by wide maximums at frequencies between 20 and 30 Hz, and relatively constant slope toward higher frequencies. Spectral level of noise changes in time in relatively wide limits. At low frequencies, below 100 Hz, the dynamics of noise level is correlated with the dynamics of water flow and speed. At higher frequencies, noise spectra are mostly influenced by human activities on river and on riverbanks. The influence of wind on noise in rivers is complex due to the annual variation of river surface. The influence of wind is less pronounced than in oceans, seas, and lakes.
The origin of vessels vibrations is dominantly determined by vessels propulsion system, auxiliary systems, pumps, breaking of the waves at the ship hull, etc. All of these systems contribute to the appearance of the underwater sound in water environment. As a source of underwater sound, vessels has the characteristic of directivity. Vibration of the vessel's structure is analyzed using spectra, but hydroacoustic signals are analyzed using spectra and higher order spectral analysis - bispectra. The measuring of the radiated hydroacoustic noise was done simultaneously with multi channel measurements of the vessels vibrations at few characteristics positions of the vessel
The localization of various acoustic sources in a battlefield (such as weapon rounds, mortars, rockets, mines, improvised explosive devices, vehicle-borne improvised explosive devices and airborne vehicles) nowadays has significant history. In acoustic source localization systems multiple sensors (such as microphones or microphone arrays), placed at known positions and networked, are used to detect signals emitted from the source and perform localization of the source. In this paper, Discrete Probability Density (DPD) method, as a method for position determination, has been used to estimate location of acoustic sources such as artillery weapons. Wavelet decomposition of the acoustic signal enables to emphasize N-wave in the time domain. Time of Arrival (TOA) estimation is realized by a statistical analysis of narrow time segment which hold Nwave. Based on the estimated TOA Time Difference of Arrival (TDOA) is calculated. TDOA presents relative time difference of arrival of the sound signal between pairs of sensors. Localization of the acoustic sources is performed by time difference estimation of acoustic signal arrivals using Discrete Probability Density method. A number of experiments with fire off mortar projectiles have been conducted in order to verify the performance of the proposed approach.
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