Browsing by Author "SOARES, CRISTIANO"
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- Acoustic observatories for ocean tomography: geometries and multi-array Matched-Field TomographyPublication . SOARES, CRISTIANO; Felisberto, P.; Jesus, SergioThe present study proposes an MFT algorithm for directly estimating a two-dimensional range-dependent or three-dimensional temperature field. The acoustic system has multiple acoustic emitters and receiver arrays according to a given geometry. The acoustic signal is emitted from one emitter at a time, and collected at multiple receiver arrays. The MFT method is adapted to iteratively produce parameter estimates for each individual environmental cell. To accomplish this, an MF processor based on a multi-array acoustic data model is considered, in order to account for acoustic data collected simultaneously at several acoustic arrays.
- 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.
- Broadband matched-field tomography using simplified acoustic systemsPublication . SOARES, CRISTIANO; Jesus, S. M.Ocean Acoustic Tomography is a remote sensing technique that has been proposed to infer physical properties of the ocean traversed by the sound field. Although its feasibility has been demonstrated, it is still not being used in a systematic way due, in a large extent, to cost and operational difficulties of standard acoustic systems. Current developments of acoustic systems go in the sense of simplifying them, both at the emitting and receiving end. Simplifying an acoustic system may represent a loss or a reduction of the amount of information contained in the observed acoustic field, possibly conducting to degradation in the inversion results. The objective of this thesis is to adapt existing array processing methods to be used in acoustic tomography and geoacoustic inversion taking into account the challenges posed by such simplifications, and to cope with the loss of available information they may represent. Two aspects are exploited with the objective of coping with the reduction of information: one is the development of a broadband data model, and the other is the development of matched-field processors based on that broadband data model, with particular emphasis in highresolution processors. Matched-field based approaches appear to be suitable to work in conjunction with the simplified acoustic systems used to collect several experimental data sets treated herein. Experimental results using simplified acoustic systems, sparse receiving arrays (active mode) on one hand, or an uncontrolled source (passive mode) on the other hand, show that it is possible to produce environmental estimates of the watercolumn and seafloor in close agreement with ground truth measurements.
- Comparing noise vessel azimuth tracking with a planar hydrophone array and a single vector sensorPublication . SOARES, CRISTIANO; Zabel, Friedrich; Jorge Maia dos Santos, Paulo; Silva, AntónioVector sensors are appealing for monitoring underwater noise due to its inherent directivity. While acoustic pressure sensors are ambiguous in all directions, vector sensors permit the aquisition of directional information through the measurement of particle velocity, which enables the possibility of azimuth tracking of underwater noise sources. The MARREAL marine observatory is a marine observatory equipped with a number of sensors and subsystems, including an acoustic acquisition system made of four hydrophones and a vector sensor. The observatory was deployed in September 2022 in Sagres, Portugal, near the Baleeira Port which is accessed by fisher boats and recreational boats. This paper shows preliminary results on azimuth estimation of boats passing in the deployment area, obtained independently with a 4- hydrophone planar array and a vector sensor. The results indicate that a single vector sensor can provide fair results on azimuth tracking of boats passing in the area. At high signal-to-noise ratio (SNR) the vector sensor is able to yield results similar to those obtained with the planar array. When the SNR is low the planar array outperforms the vector sensor with actual processing methods used.
- On the applications of a compact autonomous acoustic recorderPublication . SOARES, CRISTIANO; Martins, Celestino; Zabel, Friedrich; Silva, A.A number of acoustic A compact acoustic recorder, primarily designed for underwater noise monitoring, is presented in this paper. The Self-Register Hydrophone has been used in several occasions during the past three years, in underwater noise monitoring activities. However, this kind of device also find application in other areas such as array processing and passive acoustic monitoring of marine mammals. An overview on the application of the Self-Register Hydrophone is given herein.
- Shallow water tomography in a highly variable scenarioPublication . SOARES, CRISTIANO; Jesus, Sérgio; Coelho, Emanuel; Caiti, A.; Chapman, N. R.; Hermand, J. P.; Jesus, S. M.In October 2000, SiPLAB and the Instituto Hidrografico (IH - PN) conducted the IN-TIFANTE'00 sea trial in a shallow area off the Peninsula of Troia, approximately 50 km south from Lisbon, in Portugal. The experiment itself and results obtained in most of the data set have been reported at various occasions in the last two years. This paper focuses on the data acquired during Event 2, where the acoustic propagation path was approximately range independent and the source ship was held on station at a constant range of 5.8 km from the vertical line array. Although these conditions were, in general, relatively benign for matched-field tomography, retrieval of water column and bottom parameters over a 14-hour-long recording revealed to be extremely difficult. This paper analysis in detail the characteristics of this data set and determines the causes for the observed inversion difficulties. Is is shown that the causes for the poor performance of the conventional methods are mainly the tide induced spatially correlated noise and the relative source-receiver motion during time averaging. An eigenvalue-based criterion is proposed for detecting optimal averaging time. It is shown that this data selection procedure together with hydrophone normalization and an appropriate objective function provide a better model fit and consistent inversion results and thus a better understanding of the environmental variability.