# Eric W. GillMemorial University of Newfoundland · Electrical and Computer Engineering

Eric W. Gill

Doctor of Philosophy

## About

196

Publications

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Introduction

**Skills and Expertise**

## Publications

Publications (196)

Wetland mapping is a critical component of environmental monitoring, requiring advanced techniques to accurately represent the complex land cover patterns and subtle class differences innate in these ecosystems. This study aims to address these challenges by proposing CVTNet, a novel deep learning (DL) model that integrates convolutional neural net...

Wetlands are amongst Earth’s most dynamic and complex ecological resources, serving productive and biodiverse ecosystems. Enhancing the quality of wetland mapping through Earth observation (EO) data is essential for improving effective management and conservation practices. However, the achievement of reliable and accurate wetland mapping faces cha...

This article describes a new method to extract the peak wave period of an ocean patch based on the received electric field from a high-frequency surface-wave radar (HFSWR) illuminating that patch. The method compares favourably with others in the literature, with an RMSE of 1.81 s, and a relative RMSE of 21.9%, when compared against a wave buoy, an...

The Doppler spectra of received data from HF radars from the ocean surface have always been an important part of ocean parameter estimation for many decades [1]. Determining the Doppler spectrum from the received time series data, and then processing it, leads to the extraction of important wave parameters, such as significant wave height, peak wav...

The usual procedure for extracting ocean surface information from data acquired from a high-frequency surface wave radar transmitting from a floating platform is to first compensate for the motion of the antenna in the acquired motion-contaminated Doppler spectrum and then extract the ocean wave parameters from the motion-compensated result. The au...

Effective monitoring of wetlands plays a pivotal role in comprehending and managing these ecologically vital ecosystems. This study assesses the potential of C-band Synthetic Aperture Radar (SAR) imagery in compact polarization (CP) mode, utilizing the RADARSAT Constellation Mission (RCM), for wetland characterization. We introduce the compact-pola...

A method for time-domain motion compensation of high frequency (HF) radar signals for the case of a floating transmitter and fixed receiver is proposed when the motion parameters (including the amplitude and angular frequency of the motion) are not known a priori. In this study, the floating platform is assumed to follow a single-frequency motion m...

Despite their importance to ecosystem services, wetlands are threatened by pollution and development. Over the last few decades, a growing number of wetland studies employed remote sensing (RS) to scientifically monitor the status of wetlands and support their sustainability. Considering the rapid evolution of wetland studies and significant progre...

In a previous paper, the authors showed that up to first-order, the significant wave height from a patch of the ocean is linearly proportional to the standard deviation of the received electric field from that patch using a High-Frequency Surface-Wave radar. In previous work, this was demonstrated and verified, by using volatility estimation method...

Wetland is one of the most productive resources on earth, and it provides vital habitats for several unique species of flora and fauna. Over the last decade, mapping and monitoring wetlands by utilizing deep learning (DL) models and remote sensing data gained popularity due to the importance of wetland preservation. In general, DL-based methods hav...

In wetland mapping, a lot of uncertainty is related to the task of selecting an appropriate classification approach. Although the individual models are available and well-established in the literature for the classification task, the combination approaches have become popular recently. Hence, selecting an appropriate method is challenging, whether...

A vast array of ocean instrumentation has been developed for research purposes since the middle of the twentieth century, among which remote sensing technologies have become increasingly important. Within this class of instruments, high frequency (HF) surface and skywave radar, microwave marine radar and global navigation satellite systems (GNSS)-b...

A vast array of ocean instrumentation has been developed for research purposes since the middle of the twentieth century, among which remote sensing technologies have become increasingly important. Within this class of instruments, high frequency (HF) surface and skywave radar, microwave marine radar and global navigation satellite systems (GNSS)-b...

In order to extract target and ocean information accurately from high-frequency surface wave radar (HFSWR) data when the radar is mounted on a floating platform, motion compensation is crucial. In this study, motion compensation of the radar Doppler spectrum is performed when the motion parameters are previously unknown. Also, a dual-frequency plat...

In recent years, several powerful machine learning (ML) algorithms have been developed for image classification, especially those based on ensemble learning (EL). In particular, Extreme Gradient Boosting (XGBoost) and Light Gradient Boosting Machine (LightGBM) methods have attracted researchers’ attention in data science due to their superior resul...

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 tha...

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 Fourie...

An extension to the correction theory for the electric field and radar cross-section of the ocean surface under electromagnetically-high sea states is presented, accounting for the impact of second-order hydrodynamic interaction of waves on the total radar cross-section of the ocean surface in this case. An expression for the second-order correctio...

The extraction of oceanic wave spectrum information from radar data has been a challenging problem that has been the subject of a vast amount of research over the past several decades. This research has resulted in a multitude of approaches to extract ocean wave spectra from Doppler spectrum returns. One common feature of many of these methods is t...

Accepted to IEEE Journal of Oceanic Engineering

North America is covered in 2.5 million km 2 of wetlands, which is the remainder of an estimated 56% of wetlands lost since the 1700s. This loss has resulted in a decrease in important habitat and services of great ecological, economic, and recreational benefits to humankind. To better manage these ecosystems, since the 1970s, wetlands in North Ame...

When many people think of radar, a World War II technology, the first thing that may come to mind is films, such as "The Hunt for Red October", and monitoring airspace for incoming threats. In fact, there are many applications that are much more mundane. Among them are the monitoring of large swaths of the ocean and extraction of ocean parameters,...

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 scatte...

Detailed information on the spatial distribution of wetlands is crucial for sustainable management and resource assessment. Furthermore, regularly updated wetland inventories are of particular importance given that wetlands comprise a dynamic, rather than permanent, land condition. Accordingly, satellite-derived wetland maps are greatly beneficial,...

For close to half a century, the usual procedure to
determine ocean surface information from HF-radar data has
been to first form the Doppler spectrum from the received time
series, and then process the result to extract important wave
parameters, such as significant wave height, primary wave period,
principal wave direction, or even the full direc...

Compact high-frequency (HF) antenna arrays are convenient to deploy. However, using a small-aperture HF surface wave radar for wind direction measurement is still a challenging problem, since an unsatisfactory array pattern degrades the performance of Bragg ratio estimation. To address this issue, a digital beamforming method based on a superdirect...

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,...

Compact high-frequency surface wave radar has been widely applied to the measurement of sea surface current, but its accuracy and direction resolution of wave parameter estimation are always limited due to the wide beam of the antenna. In this article, a novel wave-height mapping method based on the second-order harmonic peak (SHP) of radar Doppler...

Shore-based coherent microwave radar and high-frequency (HF) surface wave radar are two components of a rapidly emerging set of technologies suitable for ocean wave remote sensing. To investigate their differences, this paper describes and analyzes the relationship between the water particle velocity and the wave height spectrum based on linear wav...

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 initi...

Despite the application of state-of-the-art fully Convolutional Neural Networks (CNNs) for semantic segmentation of very high-resolution optical imagery, their capacity has not yet been thoroughly examined for the classification of Synthetic Aperture Radar (SAR) images. The presence of speckle noise, the absence of efficient feature expression, and...

Compensation for platform motion in Doppler spectra acquired by HF-radar.

Detailed information on spatial distribution of wetland classes is crucial for monitoring this important productive ecosystem using advanced remote sensing tools and data. Although the potential of full- and dual-polarimetric (FP and DP) Synthetic Aperture Radar (SAR) data for wetland classification has been well examined, the capability of compact...

HF surface wave radar (HFSWR) has been recognized and accepted as an important tool for ocean remote sensing for more than four decades. In this article, a comprehensive tutorial of such an ocean sensor is presented. It begins with the concept of HFSWR. Next, the history of HFSWR is briefly reviewed. Then, the classification of HFSWR in terms of wa...

The generalized function approach for modeling radio wave scattering has been used to develop expressions for the scatter from rough surfaces and for horizontally-stratified media. The scattered field from rough surfaces can be found in closed form if plane wave incidence is assumed, but the method is valid for any realizable source without resorti...

Wetlands are one of the most important ecosystems that provide a desirable habitat for a great variety of flora and fauna. Wetland mapping and modeling using Earth Observation (EO) data are essential for natural resource management at both regional and national levels. However, accurate wetland mapping is challenging, especially on a large scale, g...

For over sixty years, the usual procedure to
determine the significant wave height from HF-radar data has
been to first form the Doppler spectrum from the received
radar data, and then process the result to extract important
ocean wave parameters, such as the significant wave height,
primary wave period, principal wave direction, or even the full
d...

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 spe...

In this paper, the effect of the ocean surface sampling process on the ocean wave spectral estimation using the Cartesian Fourier Transform (CFT) method on X-band marine radar data is investigated. Our analysis shows that the ocean surface sampling process involves a spatial averaging process that might be described as a 2D low pass filter. Further...

In 1955, Crombie [1] identified that when an electromagnetic wave is transmitted from a shore-based high-frequency (HF) radar, operating at 13.56 MHz, the Doppler spectrum of sea echo yielded a resonant backscatter phenomenon known as Bragg scattering, which results from coherent reflection of the transmitted energy by ocean surface waves (SWs) who...

The first- and second-order high-frequency radar cross sections of the ocean surface are derived for an antenna on a floating platform. In this analysis, simulations are conducted for a more complicated platform motion than appear in earlier work and comparisons are made to model outputs for a fixed antenna. Results show that motion-induced peaks a...

The first- and second-order bistatic high-frequency radar cross sections of the ocean surface are derived with a dual-frequency platform motion model. Simulations are made to illustrate how the bistatic angle affects the cross section. Not surprisingly, the energy of the second-order radar cross section is seen to decrease as the bistatic angle inc...

A method for mitigating antenna motion effects in high-frequency radar Doppler spectra developed from ocean backscatter is proposed. On the basis of the established radar cross-section models for a fixed antenna and for an antenna on a floating platform, the relationship between these models is examined. Through this relationship, motion compensati...

Ocean wind and wave parameters can be measured by in-situ sensors such as anemometers and buoys. Since the 1980s, X-band marine radar has evolved as one of the remote sensing instruments for such purposes since its sea surface images contain considerable wind and wave information. The maturity and accuracy of X-band marine radar wind and wave measu...

Since the time of Lord Rayleigh, the usual approach to find the power spectral density of the reflected electric field from a rough surface has been to represent the surface as a Fourier series, and then find the Fourier transform of the autocorrelation of this reflected E-field. This can be viewed as a correlogram approach to finding the power spe...

In this paper, sea surface wind direction and speed are obtained from X-band nautical radar images. A data control strategy is proposed to distinguish rain-free and rain-contaminated radar data. The radar data are decomposed by an ensemble empirical mode decomposition method into several intrinsic mode functions (IMFs) and a residual. A normalizati...

In this letter, an ensemble empirical mode decomposition (EEMD)-based method is proposed to estimate significant wave height (SWH) from the X-band marine radar sea surface images. First, the data sequence in each radial direction of a radar subimage is decomposed by the EEMD into several intrinsic mode functions (IMFs). A normalization scheme is th...

In the Ph.D. thesis of Gill, the author determines the power
spectral density per unit area by finding the auto-correlation
of the received voltage assuming a certain number of scatters,
and then taking its Fourier transform. Here, we instead
find the power spectral density using Welch’s periodogram
approach, where we take the Fourier transform of...

Based on the change-of-coordinates that was
previously proposed in [1], in this paper, the wave spectrum
inversion problem is solved with very high accuracy for
the case when there is little or no noise in the second-order
Doppler spectrum. The new solution is based on the
form of the forward problem, which is a sum of spatially-dependent
linear co...

Knowledge of the ocean wave spectrum, from which many important ocean parameters can be extracted, is crucial to understand the ocean’s behaviour. Due to the intricate nature of ocean wave spectrum extraction from HF radar data, previously devised methods relied on making a linear approximation to the original nonlinear problem or resorted to const...

Two ensemble empirical mode decomposition (EEMD)-based methods are presented to retrieve wind direction from rain-contaminated X-band nautical radar sea surface images. Each radar image is first decomposed into disparate intrinsic mode function (IMF) components using 1-D EEMD or 2-D EEMD. Then, the standard deviation of one IMF component or the com...

Two ensemble empirical mode decomposition (EEMD)-based methods are presented to retrieve wind direction from rain-contaminated X-band nautical radar sea surface images. Each radar image is first decomposed into disparate intrinsic mode function (IMF) components using 1-D EEMD or 2-D EEMD. Then, the standard deviation of one IMF component or the com...

In this paper, a method for extracting wind parameters from rain-contaminated X-band nautical radar images is presented. The texture of the radar image is first generated based on spatial variability analysis. Through this process, the rain clutter in an image can be removed while the wave echoes are retained. The number of rain-contaminated pixels...

A theoretical mixed-path ionospheric clutter model for bistatic high frequency radar is presented. Based on previous monostatic work, the first-order received electric field for bistatic radar is derived by considering the scattering processes on both the ionosphere and the ocean surface. Then, the first-order received power model is developed by i...

A theoretical second-order monostatic high frequency radar power model is derived for the case of mixedpath ionosphere-ocean propagation. Firstly, the general form of the received electric field is investigated by considering the ionospheric reflection and the second-order sea scattering, which involves both electromagnetic and hydrodynamic contrib...

The purpose of this paper is to survey and assess the state-of-the-art in automatic target recognition for synthetic aperture radar imagery (SAR-ATR). The aim is not to develop an exhaustive survey of the voluminous literature, but rather to capture in one place the various approaches for implementing the SAR-ATR system. This paper is meant to be a...

A theoretical model of the first-order high-frequency (HF) radar cross section (RCS) for the ionosphere–ocean propagation involving a frequency-modulated continuous wave (FMCW) source is presented in this paper. Based on previous modeling involving the scattering of HF electromagnetic radiation from the ocean surface, an expression for the first-or...

A two-dimensional ensemble empirical mode decomposition (2D-EEMD)-based method is presented to improve wind direction retrieval from rain-contaminated X-band nautical radar sea surface images. 2D-EEMD is first implemented to decompose each rain-contaminated radar image into several intrinsic mode function (IMF) components. Then, a harmonic function...

The first-order high frequency radar cross section of the ocean surface is derived for an antenna on a floating platform. In this analysis, simulations are conducted for more complicated platform motion than appear in earlier work and comparisons are made to model outputs for a fixed antenna. Results show that motion-induced peaks appear symmetrica...

Since the observation of Crombie in [1], of
Bragg peaks in high-frequency radar Doppler data, the
extraction of ocean wave parameters from such data has
become a topic of extensive research. In this paper, we
propose a new method for the extraction of the ocean
wave spectrum from high-frequency second-order Doppler
radar data. The basis of the prop...

A comparative study of the periodogram method and high-resolution techniques (the autoregressive and multiple signal classification methods) for current mapping by a high-frequency (HF) surface wave radar is undertaken for the case of 66-s-long data. This analysis is extended from a previous study that used the commonly adopted 6–13-min coherent in...

The errors in the current radial velocity measurements are examined using Bartlett beamforming and Multiple Signal Classification (MUSIC) direction-finding algorithms with a linear phased array antenna system. A variety of radar and environmental parameters are examined. Suggestions for the optimal choice of operating parameters are proposed. The M...

The first- and second-order bistatic high frequency radar cross sections of the ocean surface with an antenna on a floating platform are derived for a frequency-modulated continuous wave (FMCW) source. Based on previous work, the derivation begins with the general bistatic electric field in the frequency domain for the case of a floating antenna. D...

The second-order bistatic high frequency radar cross section of ocean surface is derived for the case of a fixed receiver and a floating transmitter. The second-order radar cross section contains both the hydrodynamic contribution and the electromagnetic contribution. The second-order hydrodynamic contribution is obtained based on the first-order b...

In this article, a comparison of signal-to-noise ratio (SNR) and shadowing-based algorithms for ocean wave height estimation from ship-borne X-band nautical radar sea surface images is presented. Modifications, including selecting a subarea along the upwind direction and smoothing the edge pixel intensity histogram, are made to the original shadowi...

High frequency surface wave radars have been used to measure ocean surface parameters, among which wind speed is the most challenging to estimate. Existing wind methods are only applicable to fully-developed, unlimited fetch seas. Here, a method is proposed for determining wind speeds for a fetch-limited sea. By differentiating the second-order rad...

A second-order monostatic high frequency radar power model is derived for the case of mixed-path ionosphere-ocean propagation with a pulsed source. This model is investigated by considering both ionospheric reflection and second-order sea surface scattering. The latter involves both electromagnetic and hydrodynamic contributions. The second-order p...

In this paper, the retrieval of sea surface current velocity from vertically polarized (V-pol) X-band marine radar data is presented. Three different methods, including the iterative least square approach, the normalized scalar product method, and the polar current shell algorithm, that have been used for horizontally polarized data are employed he...

Discarding the phase content of signals from single-channel high-frequency (HF) radar is commonplace among practitioners in the field. From the perspective of complex-valued statistics, this practice implicitly implies that the complex-valued HF data is second-order proper or circular. This paper presents a preliminary investigation into the validi...