https://hdl.handle.net/ripcmb/30233 2026-04-22T23:59:10Z 2026-04-22T23:59:10Z Pereira, Doulgas Luiz da Silva https://hdl.handle.net/20.500.14867/848289 2026-03-27T12:28:48Z 2015-01-01T00:00:00Z

Título: Improving shallow-water multibeam target detection at low grazing angles Autor(es): Pereira, Doulgas Luiz da Silva Descrição: Beyond approximately 60º incidence angle, many modern multibeam echo sounders have difficulty maintaining sufficient depth accuracy and seabed target detection to comply with International Hydrographic Organization (IHO) standards. In some cases, a target at such a low grazing angle is not detected due to limitations of the existing bottom detection method and filters applied by the manufacturer. In lieu of clear positive bathymetric indicators, a data gap within the bathymetric surface or a shadow in the backscatter image may be the only indication of the presence of that target. This research presents a refined bottom detection algorithm based on the Bearing Direction Indicator (BDI) method. The BDI approach can markedly improve target detection capability at low grazing angles in shallow waters by independently discriminating each echo’s direction of arrival irrespective of the beam spacing. The algorithm can be applied in post-processing as long as the water column data is retained. Two test datasets were collected using an EM 2040D employing angular sectors as wide as +/-82°. Data were acquired over a site with multiple IHO-compliant anthropogenic objects to assess the EM 2040D ability to detect low-grazing-angle targets prior to, and after, application of the newly developed algorithm. Results obtained clearly illustrate that the BDI algorithm can enhance low-grazing-angle target detection/definition. Tipo: doctoralThesis

2015-01-01T00:00:00Z Pinheiro, Flávia Rodrigues https://hdl.handle.net/ripcmb/847031 2024-10-17T11:52:02Z 2018-01-01T00:00:00Z

Título: Nonlinear data assimilation using synchronisation in a particle filter Autor(es): Pinheiro, Flávia Rodrigues Descrição: Current data assimilation methodologies still face problems in strongly nonlinear systems. Particle filters are a promising solution, providing a representation of the model probability density function (pdf) by a discrete set of particles. To allow a particle filter to work in high-dimensional systems, the proposal density freedom is a useful tool to be explored. A potential choice of proposal density might come from the synchronisation theory, in which one tries to synchronise the model with the true evolution of a system using one-way coupling, via the observations, by adding an extra term to the model equations that will control the growth of instabilities transversal to the synchronisation manifold. Efficient synchronisation is possible in low-dimensional systems, but these schemes are not well suited for high-dimensional settings. The first part of this thesis introduces a new scheme: the ensemble-based synchronisation, that can handle high-dimensional systems. A detailed description of the formulation is presented and extensive experiments in the nonlinear Lorenz96 model are performed. Successful results are obtained and an analysis of the usefulness of the scheme is made, bringing inspiration for a powerful combination with a particle filter. In the second part, the ensemble synhronisation scheme is used as a proposal density in two different particle filters: the Implicit Equal-Weights Particle Filter and the Equivalent-Weights Particle Filter. Both methodologies avoid filter degeneracy by construction. The formulation proposed and its implementation are described in detail. Tests using the Lorenz96 model for a 1000-dimensional system show qualitatively reasonable results, where particles follow the truth, both for observed and unobserved variables. Further tests in the 2-D barotropic vorticity model were also performed for a grid of up to 16,384 variables, also showing successful results, where the estimated errors are consistent with the true errors. The behavior of the two schemes is described and their advantages and issues exposed, as this is the first comparison ever made between both filters. The overall message is that results suggest that the combination of the ensemble synchronisation with a particle filter is a promising solution for high-dimensional nonlinear problems in the geosciences, connecting the synchronisation field to data assimilation in a very direct way. Tipo: doctoralThesis

2018-01-01T00:00:00Z De Deus, João Celso Silva https://hdl.handle.net/ripcmb/846956 2024-06-05T16:30:01Z 2023-12-01T00:00:00Z

Título: AN EXPLORATION OF CONVENTIONAL BEAMFORMING APPLIED TO A PHASE MEASURING SONAR Autor(es): De Deus, João Celso Silva Descrição: Brazilian rivers are a particularly challenging navigation environment because of frequent changes in bathymetry due to sediment transport. To accelerate the production of hydrographic information for these regions, the Brazilian Hydrographic Office has been investigating efficient ways of riverine surveying. In this context, Phase Measuring Bathymetric Sonars (PMBS) are being considered because of their potential to provide wider swaths than traditional Multibeam Echo Sounders (MBES) in shallow waters. Although these systems historically had severe limitations in sounding quality and nadir density, new models with multiple stave pairs are being built to overcome these issues, including the EdgeTech 6205, which claims to use beamforming to resolve nadir gaps, a long-term problem of PMBS. This research reproduced conventional phase detection algorithms and compared them to an in-house developed differential phase Direction of Arrival (DOA) estimator, which uses phase- shift beamforming to constrain the receiver elevation angle sensitivity. To assess the 6205’s performance, a shallow water region, known to have varying seafloor characteristics, such as rough, smooth, target-filled, and a seafloor depth gradient, was investigated by both an EdgeTech 6205 and, as a benchmark reference, an MBES Kongsberg EM2040P, already well-assessed and used in high-quality hydrographic surveys around the world. Depths were comparable to shallow rivers to assess if it would provide reasonable quality and efficiency for riverine surveys. The results obtained indicated that the use of beamforming significantly contributed to the suppression of multipath and noise. At the same time, the system evaluation attested to its potential to be used in hydrographic surveys, being an efficient alternative to conventional multibeam systems for IHO S-44 Order 1 riverine surveys. Tipo: masterThesis

2023-12-01T00:00:00Z Nadaf, Elias de Castro https://hdl.handle.net/ripcmb/846481 2024-01-22T17:56:39Z 2022-01-01T00:00:00Z

Título: Exploring turbulent wakes in a non-uniformly stratified environment for submarine detection Autor(es): Nadaf, Elias de Castro Descrição: This study aims to explore the behavior of turbulent wakes generated by a spherical submerged body propagating with constant speed in a non-uniformly stratified fluid. The investigation is based on a series of high-resolution numerical simulations in which the background stratification is systematically varied. We consider one linear and five non-linear temperature profiles and two sets of Froude numbers (Fr), Fr = 1.0 and Fr = 3.2. The analysis of dissipation of thermal variance (χ) shows that the shape of the wake for non-uniform profiles is more horizontally spread, and internal waves are much stronger than in linear stratification. Experiments with Fr = 1.0 show a rather asymmetric energy distribution caused by internal wave reflections from low-gradient regions. An idealized model demonstrates that internal waves emitted at horizontal angles shallower than roughly 64 degrees are reflected. For Fr = 3.2, internal waves are radiated at steeper angles and transmitted more. Using decay rates of χ, the maximum detection time of the wake can be estimated, showing that for Fr = 3.2, the thermal signal lasts four to five times longer than for Fr = 1.0. Furthermore, concave profiles produce signals lasting approximately twice as long as those for linear profiles, whereas low-gradient types have half the duration. This research is expected to assist in the development of non-traditional detection algorithms for undersea warfare. Tipo: doctoralThesis

2022-01-01T00:00:00Z