Levent Sevgi

An integrated maritime surveillance system based on high-frequency surface-wave radars. 1. Theoretical background and numerical simulations

An integrated maritime surveillance (IMS) system, based on high-frequency surface-wave radars (HFSWR), is described. IMS provides low-cost, 24-hour, real-time, over-the-horizon surveillance of large ocean areas, out to the 200 nautical mile Exclusive Economic Zone (EEZ). The system can be used to coordinate search and rescue operations, and to combat smuggling, drug trafficking, illegal dumping of pollutants, and other undesirable activities. The major challenges in using HFSWR are (i) operating within the crowded HF spectrum; and (ii) maintaining effective operation in high environmental noise, ocean clutter, ionospheric clutter and other undesirable sources of interferences. The system is outlined and these problems are addressed. Numerical simulation, as well as stochastic modeling, are presented to demonstrate the physics behind the system.

Complex Electromagnetic Problems and Numerical Simulation Approaches

PART I: NUMERICAL SIMULATION APPROACHES.PART II: APPLICATIONS.Ground Wave Propagation Modeling.Antenna Analysis and Array Processing.RCS Predicting and Reduction.Microwave Networks.EMC-BEM Modeling.Radar Simulation.Appendix A: EM Fundamentals.Appendix B: Tables of Computer Codes.Index.

An integrated maritime surveillance system based on high-frequency surface-wave radars. 2. Operational status and system performance

For pt.1 see ibid., vol.43, no.4, p.28-43 (2001). An integrated maritime surveillance (IMS) system, based on high-frequency surface wave radars (HFSWR), for monitoring surface and low-level air activity within the 200 nautical mile (nm) Exclusive Economic Zone (EEZ) is described in this two-part paper. The science behind the long-range performance of HFSWR was presented in Part 1(Sevgi et al. 2001). The system described was installed on Canadas east coast, where it is being used to demonstrate continuous, all-weather surveillance of the EEZ to beyond 200 nm. The system consists of two land-based HFSWRs and an operations control center (OCC). The two unmanned radars provide coverage of the Grand Banks region of Newfoundland, renowned for its offshore resources, particularly fish and oil. The system has been designed to assist authorities to more efficiently monitor such illegal activities as drug trafficking, smuggling, piracy, illicit fishing and illegal immigration. In addition, the system may be used for tracking icebergs, environmental protection, search and rescue, resource protection, sovereignty monitoring, and remote sensing of ocean surface currents and winds. Extensive performance testing of the system has been conducted using the two fully functional radars. It is shown that the HFSWR system complements existing surveillance assets to dramatically increase the effectiveness of air and surface reconnaissance missions by vectoring them directly to targets of interest.

A novel finite-difference time-domain wave propagator

A novel time-domain wave propagator is introduced. A two-dimensional (2-D) finite-difference time-domain (FDTD) algorithm is used to analyze ground wave propagation characteristics. Assuming an azimuthal symmetry, surface, and/or elevated ducts are represented via transverse and/or longitudinal refractivity and boundary perturbations in 2-D space. The 2-D FDTD space extends from x=0 (bottom) to x/spl rarr//spl infin/ (top), vertically and from z/spl rarr/-/spl infin/ (left) to z/spl rarr//spl infin/ (right), horizontally. Perfectly matched layer (PML) blocks on the left, right, and top terminate the FDTD computation space to simulate a semi-open propagation region. The ground at the bottom is simulated either as a perfectly electrical conductor (PEC) or as a lossy second medium. A desired, initial vertical field profile, which has a pulse character in time, is injected into the FDTD computation space. The PML blocks absorb field components that propagate towards left and top. The ground wave components (i.e., the direct, ground-reflected and surface waves) are traced longitudinally toward the right. The longitudinal propagation region is covered by a finite-sized FDTD computation space as if the space slides from left to right until the pulse propagates to a desired range. Transverse or longitudinal field profiles are obtained by accumulating the time-domain response at each altitude of range and by applying the discrete Fourier transformation (DFT) at various frequencies.

Numerical Investigations of and Path Loss Predictions for Surface Wave Propagation Over Sea Paths Including Hilly Island Transitions

Surface wave propagation along multi-mixed-paths with irregular terrain over spherical Earth in two-dimension (2D) is discussed. For the first time in the literature, sea-land-sea (island) transition problem including non-flat (hilly) islands is investigated systematically. A finite element method based multi-mixed path surface wave virtual propagation predictor tool FEMIX is developed for this purpose. FEMIX, tested and calibrated against analytical ray-mode reference models accommodated with the Millington curve fitting approaches, is shown to be capable of modeling propagation along sea surface having multiple hilly islands over MF (300 kHz - 3 MHz) and HF (3 - 30 MHz) bands.

A mixed-path groundwave field-strength prediction virtual tool for digital radio broadcast systems in medium and short wave bands

The emerging digital technologies for the communication bands from LF up to VHF - bands traditionally used by analog radio systems - necessitate revisiting early analytical propagation methods, and urge engineers to develop novel propagation prediction tools. Existing analytical propagation techniques are based on ray-mode approaches and the Millington curve-fitting approach for mixed-path propagation. These have been endorsed and are used in related ITU (formerly, CCIR) recommendations. These techniques are discussed, with characteristic examples produced via a newly introduced MF/HF groundwave propagation prediction virtual tool (GPVT)

Wave propagation inside a two-dimensional perfectly conducting parallel-plate waveguide: hybrid ray-mode techniques and their visualizations

This work is intended as an educational aid, dealing with high-frequency (HF) electromagnetic wave propagation in guiding environments. It is aimed at advanced senior and first-year graduate students who are familiar with the usual engineering mathematics for wave equations, especially analytic functions, contour integrations in the complex plane, etc., and also with rudimentary saddle-point (HF) asymptotics. After an introductory overview of issues and physical interpretations pertaining to this broad subject area, detailed attention is given to the simplest canonical, thoroughly familiar, test environment: a (time harmonic) line-source-excited two-dimensional infinite waveguide with perfectly conducting (PEC) plane-parallel boundaries. After formulating the Greens function problem within the framework of Maxwells equations, alternative field representations are presented and interpreted in physical terms, highlighting two complementary phenomenologies: progressing (ray-type) and oscillatory (mode-type) phenomena, culminating in the self-consistent hybrid ray-mode scheme, which usually is not included in conventional treatments at this level. This provides the analytical background for two educational MATLAB packages, which explore the dynamics of ray fields, mode fields, and the ray-mode interplay. The first package, RAY-GUI, serves as a tool to compute and display eigenray trajectories between specified source/observer locations, and to analyze their individual contributions to wave fields. The second package, HYBRID-GUI, may be used to comparatively display range and/or height variations of the wave fields, calculated via ray summation, mode-field summation, and hybrid ray-mode synthesis.

The Split-Step-Fourier and Finite-Element-Based Parabolic-Equation Propagation-Prediction Tools: Canonical Tests, Systematic Comparisons, and Calibration

Powerful propagation-prediction tools, based on the split-step Fourier-transform and the Finite-Element-Method (FEM) solutions of the parabolic equation (PE) are discussed. The parabolic equation represents one-way propagation, and is widely used in two-dimensional (20) groundwave propagation modeling. It takes the Earths curvature, the atmospheric refractivity variations, non-flat terrain scattering, and the boundary losses into account. MA TLAB-based numerical split-step parabolic-equation and Finite-Element-Method parabolic-equation routines were developed. These were used in canonical tests and comparisons to illustrate that the parabolic equation accounts for all of these effects. Both tools were calibrated against an analytical exact solution.

Groundwave Modeling and Simulation Strategies and Path Loss Prediction Virtual Tools

Reliable and accurate groundwave propagation path loss prediction between a pair of transmitter/receiver necessitates a good understanding of electromagnetic wave scattering in the presence of non-flat terrain and inhomogeneous atmosphere, and this is one of the major issues in radio communication and radar systems design. A propagation engineer desires to have a numerical propagator that calculates the radiowave path loss, without going into details and/or having a deep knowledge of the propagation phenomena, between any two points specified on a digital map of the area of interest. Since a generally applicable, all-purpose propagation prediction method has not developed yet one has to understand validity and accuracy ranges, and the limitations of available prediction models and tools; this certainly requires, to some extent, the physical insight of the propagation problem at hand. This article aims to summarize groundwave propagation modeling and numerical simulation strategies, and to review some of the virtual tools, introduced recently.

A Novel MoM- and SSPE-based Groundwave-Propagation Field-Strength Prediction Simulator

Knowledge of the local groundwave-propagation characteristics is essential in wireless systems. Although Maxwells equations establish the theoretical background, only a limited number of highly idealized groundwave-propagation problems have mathematically exact and/or approximate solutions. Therefore, semi-analytical/numerical and pure numerical simulation methods are almost the only way to handle realistic groundwave-propagation problems. To a certain extent, numerical simulators should be capable of taking non-flat, penetrable terrain and inhomogeneous atmospheric effects into account. Unfortunately, a generally applicable simulator has not yet appeared; there are many methods that have been developed under different assumptions and approximations, valid in different parameter regimes. It is therefore a challenge to apply these methods to the same physical problems, to do comparisons, and to evaluate numerical results. With all these factors in mind, a new MATLAB-based package GrMoMPE is introduced. It is first validated and calibrated, and then applied to some characteristic groundwave-propagation problems. The introduction of GrMoMPE has made it possible to do direct and accurate comparisons and reliable physical interpretations.