Publications

Journal Papers

1. IEEE

   High-Frequency Radar Cross Section of the Ocean Surface With Arbitrary Roughness Scales: Higher Order Corrections and General Form

   Murilo Teixeira Silva, Weimin Huang, and Eric W. Gill

   IEEE Transactions on Antennas and Propagation, Oct 2021

   Abstract

   The present work shows the derivation of general forms for the expressions of the first- and second-order corrections to the radar cross section (RCS) of the ocean surface at electromagnetically high sea states. An analysis of the morphology of the correction terms and their impact on the total RCS of the ocean surface is presented. It is shown that most of the visible impact on the total RCS of the ocean surface is due to first-order hydrodynamic terms and is concentrated between the Bragg peaks. Also, second-order hydrodynamic correction terms can increase the integral over the second-order region outside the dominant Bragg peak by up to 30% at extreme ocean conditions. Although comparison with field data was not conclusive, the presented results can improve the representation of electromagnetically large waves in the total RCS of the ocean surface without dismissing the analysis methods for height-restricted RCSs presented in the literature.

2. IEEE

   High-Frequency Radar Cross Section of the Ocean Surface With Arbitrary Roughness Scales: A Generalized Functions Approach

   Murilo Teixeira Silva, Weimin Huang, and Eric W. Gill

   IEEE Transactions on Antennas and Propagation, Mar 2021

   Abstract

   A correction term for electromagnetic scattering from the ocean surface with large roughness scales in the HF band is proposed. A generalized functions’ method has been employed to obtain the operator equation of the electric field over the ocean surface. Using a dipole antenna with a pulsed sinusoidal signal at the transmitter and employing Fourier series and perturbation theory expansions of the ocean surface, three expressions were derived for the electric field up to the second order, with one of them being a correction term for the first order for large roughness scales. Through a cross section analysis, it is observed that the additional term would represent waves with both large heights and wavelengths but small slopes. This allows for the analysis of extreme wave events using HF radar, which was limited by previously derived small heights and small slope methods.

1. MDPI

   Bistatic High-Frequency Radar Cross-Section of the Ocean Surface with Arbitrary Wave Heights

   Murilo Teixeira Silva, Weimin Huang, and Eric W. Gill

   Remote Sensing, Feb 2020

   Abstract

   The scattering theory developed in the past decades for high-frequency radio oceanography has been restricted to surfaces with small heights and small slopes. In the present work, the scattering theory for bistatic high-frequency radars is extended to ocean surfaces with arbitrary wave heights. Based on recent theoretical developments in the scattering theory for ocean surfaces with arbitrary heights for monostatic radars, the electric field equations for bistatic high-frequency radars in high sea states are developed. This results in an additional term related to the first-order electric field, which is only present when the small-height approximation is removed. Then, the radar cross-section for the additional term is derived and simulated, and its impact on the total radar cross-section at different radar configurations, dominant wave directions, and sea states is assessed. The proposed term is shown to impact the total radar cross-section at high sea states, dependent on radar configuration and dominant wave direction. The present work can contribute to the remote sensing of targets on the ocean surface, as well as the determination of the dominant wave direction of the ocean surface at high sea states.

2. IEEE

   Nonlinear Extraction of Directional Ocean Wave Spectrum From Synthetic Bistatic High-Frequency Surface Wave Radar Data

   Murilo Teixeira Silva, Reza Shahidi, Eric W. Gill, and 1 more author

   IEEE Journal of Oceanic Engineering, Jul 2020

   Abstract

   This paper proposes the use of a nonlinear inversion technique for the extraction of the directional ocean wave spectrum from bistatic high-frequency surface wave radar (HFSWR) Doppler data. The extraction method is combined with nonlinear regression expressions, solely based on the Doppler data, to retrieve wind speed and direction. Once the initialization parameters have been defined, a blind iterative algorithm based on Tikhonov regularization in Hilbert Scales is used to extract the nondirectional spectrum. The extracted spectrum is then used to determine the directional factor, which is assumed to be described by a cosine-power model. The proposed method yields fairly good results with synthetic noise-contaminated HFSWR data with a priori regularization parameters.

1. AGU

   Electromagnetic Scattering in Curvilinear Coordinates Using a Generalized Functions Method

   Murilo Teixeira Silva, Eric W. Gill, and Weimin Huang

   Radio Science, Nov 2019

   Abstract

   A system of equations for calculating the electric field in curvilinear coordinates without imposing external boundary conditions is proposed. First, the system of equations is derived using generalized functions, without imposing external boundary conditions or a coordinate system. Then, in order to demonstrate the use of the system of equations, the derived system is applied to the case of a spherical scatterer, which is then narrowed to the case of a perfect electrically conducting (PEC) sphere. It is shown that for the particular case of a PEC sphere, the resulting field expression agrees with the Stratton-Chu solution for the Maxwell’s equations, confirming that the proposed method can be used to reach a general solution for the electromagnetic field scattered by a PEC sphere, which allows for the calculation of its cross section.

1. AMS

   An Improved Estimation and Gap-Filling Technique for Sea Surface Wind Speeds Using NARX Neural Networks

   Murilo Teixeira Silva, Eric W. Gill, and Weimin Huang

   Journal of Atmospheric and Oceanic Technology, Jul 2018

   Abstract

   Abstract This work presents the use of a nonlinear autoregressive neural network to obtain an improved estimate of sea surface winds, taking Placentia Bay, Newfoundland and Labrador, Canada, as a study case. The network inputs and delays were chosen through cross correlation with the target variable. The proposed method was compared with five other wind speed estimation techniques, outperforming them in correlation, precision, accuracy, and bias levels. As an extension, the temporal gap filling of missing wind speed data during a storm has been considered. Data containing a measurement gap from a 40-yr windstorm that hit the same location has been used. The proposed method filled the gaps in the dataset with a high degree of correlation with measurements obtained by surrounding stations. The method presented in this work showed promising results that could be extended to estimate wind speeds in other locations and filling gaps in other datasets.

1. WSEAS

   Alternative analytical solution for position and orientation in electromagnetic motion tracking systems

   Murilo Teixeira Silva, Eduardo Telmo Fonseca Santos, José Mário Araújo, and 1 more author

   WSEAS Transactions on Systems, Jul 2017

   Abstract

   An alternative analytical solution to six degrees-of-freedom position and attitude estimation problem is proposed. The proposed method relies on the use of Singular Value Decomposition to the transformation matrix between the currents in the transmitter and in the receiver. The proposed method is validated using synthetic data, in which a random motion is applied to the transmitter within an environment with different levels of noise. Once the efficacy of the method is confirmed, the proposed algorithm is benchmarked against a well established closedform solution. The presented method was able to accurately obtain the position and orientation, with performance comparable to the benchmark.

1. SBMAC

   Feature Extraction of Structures in Sea Water Using Self-Organizing Maps and Electromagnetic Waves

   Murilo Teixeira Silva, Lurimar Smera Batista, and Frederico Medeiros Vasconcelos De Albuquerque

   TEMA (São Carlos), Jan 2016

   Abstract

   \textlesspre\textgreater\textless!–StartFragment–\textgreaterThe use of Self-Organizing Map (\textlessspan\textgreaterSOM\textless/span\textgreater) algorithm for feature extraction and dimensionality reduction applied to underwater object detection with Low Frequency Electromagnetic Waves is presented. Computer simulation is used to generate a direct model for the study region, and a Self Organizing Map Algorithm is used to fit the data and return a similar model, with smaller dimensionality and same characteristics. Results show that virtual sensors are created by the \textlessspan\textgreaterSOM\textless/span\textgreater algorithm with consistent predictions, filling the resolution gap of the input data. These results are useful for fastening decision making algorithms by reducing the number of inputs to a group of significant data.\textless!–EndFragment–\textgreater\textless/pre\textgreater

Conference Papers

1. OCEANS

   Second-Order Correction to the HF Radar Cross-Section of the Ocean Surface at Electromagnetically-High Sea States

   Murilo Teixeira Silva, Eric W. Gill, and Weimin Huang

   In Global Oceans 2020: Singapore – U.S. Gulf Coast, Oct 2020
2. IEE APS/URSI

   HF Radar Cross-Section of Ocean Surfaces With Arbitrary Wave Heights

   Murilo Teixeira Silva, Eric W. Gill, and Weimin Huang

   In 2020 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting, Jul 2020

1. OCEANS

   Filling Gaps in Wind Speed Data – A Neural Networks Approach

   Murilo Teixeira Silva, Weimin Huang, and Eric W. Gill

   In 2018 OCEANS - MTS/IEEE Kobe Techno-Oceans (OTO), May 2018
2. OCEANS

   An Improved Nonlinear Extraction of Directional Ocean Wave Spectrum from Bistatic HFSWR Using Tikhonov Regularization in Hilbert Scales

   Murilo Teixeira Silva, Reza Shahidi, Eric W. Gill, and 1 more author

   In OCEANS 2018 MTS/IEEE Charleston, Oct 2018

1. OCEANS

   A new nonlinear approach to extraction of ocean wave spectra from bistatic Doppler HF-radar data

   Murilo Teixeira Silva, Eric W. Gill, and Reza Shahidi

   In OCEANS 2017 - Aberdeen, Jun 2017

1. ANTEM

   Sea proximity influence over EM plane wave scattering using the finite element method

   Murilo Teixeira Silva, and Lurimar Smera Batista

   In 2014 16th International Symposium on Antenna Technology and Applied Electromagnetics (ANTEM), Jul 2014

1. SBPC

   Modelagem por elementos finitos da influência da maritimidade na propagação de ondas eletromagnéticas

   Murilo Teixeira Silva, and Lurimar Smera Batista

   In Anais/Resumos da 65ª Reunião Anual da SBPC, Jul 2013

Conference Presentations

1. Effects of electromagnetically-large waves on the second-order radar cross section of the ocean surface in the HF band

   Murilo Teixeira Silva, Eric W. Gill, and Weimin Huang

   Nov 2020

1. First-order high-frequency scattering for ocean surfaces with large roughness scales

   Murilo Teixeira Silva, Eric W. Gill, and Weimin Huang

   Nov 2019
2. High-frequency radar cross-section for an ocean surface with arbitrary heights

   Murilo Teixeira Silva, Eric W. Gill, and Weimin Huang

   Aug 2019

1. Empirical initial value estimation for nonlinear extraction of ocean wave spectra from bistatic HF radar data

   Murilo Teixeira Silva, Reza Shahidi, Eric W. Gill, and 1 more author

   Nov 2018

1. The use of artificial neural networks in hindcasting and filling gaps in buoy wind speed data under extreme winds

   Murilo Teixeira Silva, Eric W. Gill, and Weimin Huang

   Nov 2017

1. A change of variables for ocean wave spectrum extraction from bistatic second-order Doppler HF-radar data

   Murilo Teixeira Silva, Eric W. Gill, and Reza Shahidi

   Nov 2016

1. Dimensionality reduction on EM data for underwater object detection using self-organizing maps

   Murilo Teixeira Silva, Lurimar Smera Batista, and Frederico Medeiros Vasconcelos Albuquerque

   Nov 2015

1. Inteligência Artificial Aplicata aod Controle e Monitoramento de Ambientes Marítmos

   Murilo Teixeira Silva, and Lurimar Smera Batista

   Oct 2013

Theses

1. Generalized functions approach to the derivation of the high-frequency radar cross-section of ocean surfaces with electromagnetically-large waves

   Murilo Teixeira Silva

   2021

1. A nonlinear approach to ocean wave spectrum extraction from bistatic HF-radar data

   Murilo Teixeira Silva

   2017

1. Electromagnetic position and orientation tracking system with six degrees-of-freedom

   Murilo Teixeira Silva

   2014