Browsing by Author "Onofre, J."
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- Blind ocean acoustic tomography: experimental results on the INTIFANTE'00 data setPublication . Jesus, S. M.; Soares, C.; Onofre, J.; Picco, O.Blind Ocean Acoustic Tomography (BOAT) is an ocean remote exploration concept similar to acoustic tomography but where both the emitted signal waveform and the source osition are unknown. BOAT consists of a minimal environmental model of the area, a broadband matched- eld processor and a genetic algorithm search procedure. This paper presents the results obtained with BOAT on part of the data set acquired during the INTIFANTE'00 sea trial, where an acoustic source was towed along both range independent and range dependent paths, with source-receiver ranges varying from 500 m up to 5.5 km and water depths varying from 70 to 120 m. The results obtained on several hours of data, show that source range and depth can be used as focalizing parameters, together with the Bartlett power to indicate model tness. Using this three parameters it becomes clear when the environment is \in focus" and when it is \out of focus" leading to realiable estimates of the geometric and environmental parameters under estimation.
- Experimental testing of the blind ocean acoustic tomography conceptPublication . Soares, C.; Jesus, S. M.; Onofre, J.; Coelho, E.; Picco, P.Acoustic focalization is a well known concept that aims at estimating source location through the adjustment of multiple environmental parameters. This paper uses the same concept for inverting water column sound speed in a blind fashion, where both source location and source emitted waveform are not known at the receiver - that is Blind Ocean Acoustic Tomography (BOAT). The results obtained with BOAT, using ship noise data received on a vertical line array in a shallow water area off the coast of Portugal, show that it is indeed possible to obtain reliable joint estimates of source location and water column sound speed. During that process, it was shown that source range and depth, and Bartlett power, where good indicators of the degree of focus of the model being used.
- Observation of acoustical signal fluctuations by time-frequency analysis methodsPublication . Palmese, M.; Bozzo, A.; Jesus, S. M.; Onofre, J.; Picco, P.; Trucco, A.In this paper, acoustic data collected in shallow water during INTIMATE00 sea trials are analysed with the aim to detect fluctuations in acoustical signals under the effect of a time-varying environment. Some time-frequency analysis methods, i.e., Gabor Expansion and Wigner-Ville Distribution, have resulted to be adequate to find out fluctuations in the received signals, in particular, such analyses reported different time-frequency behaviour in relation with different tidal conditions. The variations observed in the received acoustic data have been compared with the temperature data collected during the sea trials and the related sound-speed profiles: it has been reported that major fluctuations over time in the acoustic signal occur in correspondence of the sound-speed profile changes linked to environmental variability.
- The INTIFANTE'00 sea trial: preliminary source localization and ocean tomography data analysisPublication . Jesus, S. M.; Coelho, E.; Onofre, J.; Picco, P.; Soares, C.; Lopes, C.The INTIFANTE'00 sea trial was a multidisciplinary experiment including testing of an autonomous surface vehicle, underwater communications, source localization and acoustic ocean tomography. The results shown here will concentrate on the source localization and ocean tomography data sets. The data gathered during a 24 hour run along a range independent track shows strong oceanographic features, possibly due to internal tide signature, both on the temperature data, as measured on the thermistor chain collocated with a vertical line array(VLA), and on the acoustic data. A range dependent track between 120 and 60 m water depth, shows a highly variable channel impulse response along time and range when the source was moving outwards from the VLA. In another acoustic track, the source was navigatated across a underwater canyon where the energy was rapidly distributed over a deep acoustic channel with sound trapped well below the thermocline. Good agreement between the modeled and measured channel responses represents the rst step towards matched- eld processinglike methods such as source localization and tracking and ocean tomography.