Browsing by Author "Picco, P."
Now showing 1 - 5 of 5
Results Per Page
Sort Options
- An experimental demonstration of blind ocean acoustic tomographyPublication . Jesus, S. M.; SOARES, CRISTIANO; Coelho, E.; Picco, P.Despite the advantages clearly demonstrated by ocean acoustic tomography OAT when compared to other ocean monitoring techniques, it suffers from several technical-related drawbacks. One is the requirement for rather expensive equipment to be maintained and operated at several locations in order to obtain sufficient source–receiver propagation paths to cover a given ocean volume. This paper presents the preliminary feasibility tests of a concept that uses ships of opportunity as sound sources for OAT. The approach adopted in this paper views the tomographic problem as a global inversion that includes determining both the emitted signal and the environmental parameters, which is a similar problem to that seen in blind channel identification and was therefore termed blind ocean acoustic tomography BOAT . BOAT was tested on a data set acquired in October 2000 in a shallow-water area off the west coast of Portugal, including both active and passive ship noise data. Successful results show that BOAT is able to estimate detailed water column temperature profiles coherent with independent measurements in intervals where the uncontrolled source signal ship noise presents a sufficient bandwidth and signal-to-noise ratio, which clearly define the limitations of the presented method.
- 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.
- Passive ocean acoustic tomography: theory and experimentPublication . Marinis, E. de; Gasparini, O.; Picco, P.; Jesus, S. M.; Crise, A.; Salon, S.In this paper the Passive Ocean Acoustic Tomography (P-OAT) methodology is presented. This technique, avoiding the use of a dedicated active sound source, estimates the sea water temperature spatial distribution from the received noise emitted from ships of opportunity. The feasibility of the proposed methodology has been confirmed both by test-runs on semi-synthetic data and by the use of real acoustic and environmental data collected during INTIMATE00 experiment performed on October 2000 in the Atlantic Ocean off the Portuguese coasts.
- 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.