MARITIME FORWARD SCATTER RADAR: DATA COLLECTION AND CLUTTER ANALYSIS by Kalin Hristov Kabakchiev A thesis submitted to the School of Electronic, Electrical and System Engineering of The University of Birmingham for the degree of DOCTOR OF PHILOSOPHY December 2014 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. Abstract This thesis is the result of study into development, experimental testing and clutter analysis in a Forward Scatter Radar (FSR) designed to detect low reflectivity maritime targets at low grazing angles. The concept of such kind of maritime system is presented; its advantages for surveillance applications are described. Scattering of Electromagnetic (EM) Waves over the sea surface at different radar configurations is outlined with the focus made on forward scattering and appropriate sea clutter models. Phenomenology of the signals in FSR is examined and explained. The development of an experimental FSR hardware operating in X- and K- frequency bands for target detection and clutter analysis and its performance are described in details. It follows with the comprehensive analysis on the measured sea clutter which includes study of influence of a large number of parameters of the radar and sea conditions on the clutter spectral and statistical properties. Finally preliminary analysis of radio frequency (RF) target signatures made with the prototype radar is presented. Acknowledgements Firstly, I would like to express my gratitude to my supervisors Prof. M. Cherniakov and Dr. M. Gashinova for the inspiration, guidance and support they provided me throughout the whole process of my studies and research. I would also like to thank Dr. E. Hoare, Dr. V. Sizov and Mr. L. Daniel for the support, knowledge and skills that I acquired from them. Glossary of Abbreviations ACC Autonomous Cruise Control ADC Analog-to-Digital Convertor AEW Airborne Early Warning ATC Air Traffic Control ATDT Automatic Target Detection and Tracking AWG Arbitrary Waveform Generator BPF Band Pass Filter BRSC Bistatic Radar Cross Section CDF Cumulative Distribution Function CLT Central Limit Theorem DPO Digital Phosphor Oscilloscope DRC Doppler Receiver Channel EEZ Effective Economic Zone EM Electromagnetic FS Forward Scattering FS CS Forward Scatter Cross Section FSML Forward Scatter Main Lobe FSR Forward Scatter Radar GIT Georgia Institute of Technology HF High Frequency HPF High Pass Filter ISAR Inverse Synthetic Aperture Radar LOS Line Of Sight MLE Maximum Likelihood Estimation MIMO Multiple-Input and Multiple-Output MISL Microwave Integrated Systems Laboratory NMRCS Normalised Monostatic Radar Cross Section NRCS Normalised Radar Cross Section OTH Over-the-Horizon Radar PDF Probability Density Function PO Physical Optics PRF Pulse Repetition Frequency PSD Power Spectral Density PTD Physical Theory of Diffraction RF Radio Frequency ROTHR Raytheon’s Relocatable Over-the-Horizon Radar RCS Radar Cross Section Rx Receiver SAR Synthetic Aperture Radar SCR Signal-to-Clutter Ratio SNR Signal-to-Noise Ratio SS Sea State T/R Transmit/Receive Device TLR Target-to-Leakage Ratio TRP Two-Ray Path Tx Transmitter VSWR Voltage Standing Wave Ratio WMO World Meteorological Organisation List of Symbols α Azimuth of the target A Effective aperture of the receiving antenna 퐴퐷푃 Phase Signature Amplitude for the Direct Path Signal 퐴푇퐺 Phase Signature Amplitude for the Scattered Signal Bn Receiver bandwidth β Bistatic angle c Speed of light (c = 3.108 m/s) D Baseline Length Ded Effective Target Dimension ∆푓푀 Fluctuation Spectrum Bandwidth ∆휏푀 Coherent Analysis Time ∆휏퐹푆 Target Visibility Time in FSR Edir Intensity of the electric component of the direct field Escat Intensity of the electric component of the scattered field ES Electric component of the shadow field EΣ Full scattered field fB Bistatic Doppler shift fd Doppler frequency shift f0 Transmitted frequency fTgt Bistatic Doppler shift caused by the target motion F Propagation Gain hR Receiver antenna height hT Transmitter antenna height htg Target height ν Target speed νr Radial velocity of the target 휈푡 Speed of Moving Target λ Wavelength of the radio waves σ Radar Cross Section 휎0 Normalised Radar Cross Section σtot Total Scattering Cross Section δ Elevation of the target δT Aspect angle of Tx δR Aspect angle of Rx N Overall noise power Gt Transmitted antenna gain Gr Received antenna gain k The wave number defined by k = 2π/λ La Propagation loss τ Radar Pulse Width LT-tg Transmitter-to-target propagation loss Ltg-R Target-to-receiver propagation loss ρ Signal-to-noise ratio Pcoherent Mean Value of the Received Signal Pcoherent Mean Signal Variance Pr Power returning to the receiving antenna Pt Transmitted power R Range to the target in meters Rt Range from Tx to target Rr Range from Rx to target RX Receiver Position ∆푅 Range Resolution SDP Direct Path Signal 푆푅퐼 Receiver Input STG Scattered Target Signal O Order t Time of Direct Signal Arrival at the Receiver tsh Delay Time of the Signal from Moving Target ∆푇 Round-trip time delay TX Transmitter position Ts System noise temperature in Kelvin TV Target Visibility Time V Magnitude of velocity vector of the target VR Receiver’s velocity vector of magnitude VT Transmitter’s velocity vector of magnitude 휔0 Carrier Frequency ωd Doppler angular Frequency 휔푑푝 Doppler Frequency Shift of the Moving Target. θ Angle made by the target trajectory and the line joining radar and target x, y, z Cartesian coordinates Table of Contents Chapter 1 Introduction ............................................................................................................... 1 Radar Basic Operation and Definition. ....................................................................... 1 Doppler Relationships ............................................................................................... 11 Radars used for Maritime Surface Observation ........................................................ 13 Maritime Clutter Problems and Basic Models .......................................................... 16 Forward Scatter Radar Brief History, Basic Operation and Definition .................... 17 Possible Applications of FSR in Maritime Environment .......................................... 22 Buoys/Shore Mounted FSR Sensors – The Concept ................................................. 24 PhD Research Problem Setting (aim, objectives) ..................................................... 29 Thesis Structure ......................................................................................................... 31 Chapter 2 Sea Clutter Models and Phenomenology of Signals in Maritime FSR ................... 32 Sea Clutter Models .................................................................................................... 32 Phenomenology of Signals in Maritime FSR ............................................................ 46 Conclusions ............................................................................................................... 62 Chapter 3 Test Equipment and Methodology .......................................................................... 63 Experimental Systems ............................................................................................... 63 Experimental Sites..................................................................................................... 68 Experimental Programme and Methodology ............................................................ 81 Data base structure .................................................................................................... 98 Conclusions ............................................................................................................. 107 Chapter 4 Sea Clutter Analysis .............................................................................................. 108 Radar Operational regimes ...................................................................................... 108 Test Scenarios ......................................................................................................... 130 Environmental Conditions....................................................................................... 132 Conclusions ............................................................................................................. 144 Chapter 5 Preliminary FSR Target Analysis ......................................................................... 150 Received Signal Characterization in FSR ............................................................... 151 Variation of Target Signature with Baseline Crossing Angle ................................. 159 Quantification of Doppler Signature with Velocity ................................................ 166 Variation of Target Signature with Polarisation ..................................................... 171 Quantification of Doppler Spectrum with Variation in Antenna Height ................ 176 Coherent processing for Maximum Effective Detection Range