DOCSLIB.ORG

Interpretation and Utilization of the Echo

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Interpretation and Utilization of the Echo PROCEEDINGS OF THE IEEE, VOL. 62, NO. 6, JUNE 1974 673 Sea Backscatter at HF: Interpretation and Utilization of the Echo DONALD E. BARRICK, MEMBER, IEEE, JAMES M. HEADRICK, SENIOR MEMBER, IEEE, ROBERT W. BOGLE, DOUGLASS D. CROMBIE AND Abstract-Theories and concepts for utilization of HF sea echo are compared and tested against surface-wave measurements made from San Clemente Island in the Pacific in a joint NRL/ITS/NOAA Although the heights of ocean waves are generally small experiment. The use of first-order sea echo as a reference target for in terms of these radar wavelengths, the scattered echo is calibration of HF over-the-horizon radars is established. Features of the higher order Doppler spectrum can be employed to deduce the nonetheless surprisingly large and readily interpretable in principal parameters of the wave-height directional. spectrum (i.e., terms of its Doppler features. The fact that these heights are sea state); and it is shown that significant wave height can be read small facilitates the analysis of scatter using the perturbation from the spectral records. Finally, it is shown that surface currents approximation. This theory [2] produces an equation which and current (depth) gradients can be inferred from the same Doppler 1) agrees with the scattering mechanism deduced by Crombie sea-echo records. from experimental data; 2) properly predicts the positions of I. INTRODUCTION the dominant Doppler peaks; 3) shows how the dominant echo magnitude is related to the sea wave height; and 4) per­ mits an explanation of some of the less dominant, more com­ T WENTY YEARS ago Crombie [1] observed sea echo plex features of the sea echo through retention and use of the with an HF radar, and he correctly deduced the scatter­ higher order terms in the perturbation analysis. Hence the ing mechanism which accounted for the peculiar and dominant spectral features explained by the simple, lowest unique dominant peaks in the observed Doppler spectrum. order terms of the perturbation analysis are referred to as This gave rise to further research and suggested the exciting "first-order" sea echo, while the remaining, less dominant fea­ possibility of measuring sea state at great distances with HF tures are termed "higher order" because they arise from the sky-wave radars. A current joint program involving NOAA, smaller (i.e., second-order, third-order, etc.) terms. NRL, and ITS on San Clemente Island has provided data for By way of introduction to the basic type of HF echo testing three possible applications of HF sea echo: 1) as a records upon which the discussion in this paper is based, we standard or reference target for calibrating the sensitivity show a typical received Doppler spectrum in Fig. 1. This plot of sky-wave radars; 2) as a means of deducing sea state (viz., represents the received signal power versus normalized Dop­ the dominant features of the wave-height directional spec­ pler shift± from the carrier (the carrier being located at zero, trum); and 3) as a method for measuring surface-current and the predicted positions of the dominant peaks at posi­ features. HF, as considered here, extends from the broadcast tions 1). Details of the conditions and system behind this band to VHF, including radar wavelengths between 10 and spectral record will be discussed later, but for now we refer 200 m. to it to illustrate how the three previously+1) claimed applica­ tions will be subsequently developed from data such as these. Manuscript received September 12, 1973; revised January 21, 1974. D. E. Barrick is with the Wave Propagation Laboratory, National 1) The dominant, first-order peak (near will be tested for Oceanic and Atmospheric Administration, Boulder, Colo.80302. use as a standard or reference echo. 2) The higher order J. M. Headrick and R. W. Bogle are with the Naval Research Lab­ oratory, Washington, D. C. 20375. Doppler features (i.e., their shapes, peak positions, and am­ D. D. Crombie is with the Institute for Telecommunication Sciences, plitudes) will be used to deduce sea state. 3) The overall shift Boulder, Colo.80302. of the first-order echo peaks from ± 1 will be used to deduce 614 PROCEEDINGS OF THE IEEE, JUNE 1974 :p--qqFirst-order sea echo 4 Fig. 2. Buoy-measured nondirectional wave-height spectra for morning (dashed) and afternoon (solid)of December 4, 1972. Triangle is model used in theoryto approximate afternoon spectrum. tional to the heightof this wave component squared. Hence it 0-21 -I 0 I 2 is evident that measurement of the first-order radar cross Normalized Doppler Frequency section of the seaversus radar operating frequencywill deter- . Example of an averaged radar sea-echo Doppler epectrum at 9.4 mine thewater-wave spectrum along theradar azimuthal MHz. Carrierwould appear at center,with *1 corresponding to bearing. By looking along several bearings, one can thereby Doppler shifts k0.313 Hz from the carrier. Resolution is 4.01 Hz. construct the “wave-height directional spectrum,”a quantity which has heretofore defied simple measurement by oceanog- (radial) currents. Since the radar echo is produced by scatter raphers. However, the radar frequency region corresponding from ocean waves, the approach taken in this paper is to re- to the importantlong-wave portion of the gravity-wave spec- late the echo features to surface features. Ocean waves and trum responsible for “sea state” spans the region from about currents are largely produced by winds, and thus one should 300 kHzto 5 MHz.Constructing and calibrating an azi- be able to ultimately deducewind features from these echoes; muthal scanning radar which sweeps over this region would this is the approach taken in parallel analyses of HF sea echo be a formidable task, in addition to the difficulty that this by Ahearn et al. [3] and Long and Trizna [4]. frequency region is already heavily occupied by users (broad- cast band, marine band, etc.). Furthermore, propagation at 11. BACKGROUNDAND INTERPRETATION these lower frequencies is restricted to ground wave (limiting Let us explain the simple interpretation of the first-order the radar range to <200 km), since ionospheric modes will Dopplerspikes of Fig. 1 as firstdeduced byCrombie [l]. be severely attenuated most of the time. Though the sea to a casual observer generally looks like a Incontrast, sea scatterin the upper HF region (6-30 random, moving, scattering surface, the dominant, crisp, and MHz), at which ionospheric propagation to great distances equally displaced Doppler peaks lead one to believe that the (-4000 km) is favored, is of a somewhat different character. radar is actually observing twotargets moving radially at The first-order resonant peaks are still evident and usually discrete readily identifiable velocities. Thefact that these dominant, as shown in Fig. 1. However, other features in the Doppler displacements are observed to vary with the square Doppler spectrum are also present, and these features appear root of the carrier frequency suggests something unique aboutto vary more significantly with sea state than do the first- HF sea echo in contrast to echoes from other moving targets. order echopeaks. These additional features are referred to Since it is well known that gravitywaves in deep water travel as “higher order,” of which “second-order” effects are felt to at a phase velocity proportional to the square root of their be the dominant contributors. On the other hand, the larger lengths L (Le., Y= dgL/2*, where g is the gravitational con- fimt-order echo is for the most part constant andinsensitive to stant), then the length of the waves producing scatter can be sea state. The reasonfor this is that the wavesproducing uniquelydeduced from the radar-derived “target” velocity. scatter, being half the radar wavelength, vary in length be- This length (for backscatter near grazing incidence) is pre- tween 25 and 5 m. Waves of this length on the open-oceans cisely one-half the radar wavelength, and explains theob- are nearly always present and are developed to their maxi- served square-rootrelationship between the Doppler and mum allowableheight, as limited by breaking. This region carrier frequencies. Thus the Ocean wave trains are behaving of the wave-height spectrum in which saturation occursis like a series of diffraction gratings, only one of which has the called the equilibrium region; Phillips [6] has shown that the orientation and spacing to scatter back toward the radar (to nondirectional temporal wave-height spectrum should follow first order). This is the double set of sea wave trains with an f5 law (jequals wave frequency in hertz) in this region. L=X/2 (or K= 2k0, where X is the radar wavelength, with Fig. 2 isa buoy measurement of this spectrumat two different K = 2*/L and ko = 2*/x being the scatteringOcean wavenumber times for 20- and 25-knot wind-driven seas in the scattering and radar wavenumber, respectively) moving radially toward area off San Clemente Island. The r5saturation region is and away from the radar.Hence the double Dopplerecho pair. clearly evident in these records; a scale at the bottom shows Theory [2], [SI alsoshows that the backscattered echo that the radar frequencies at which first-order scatter would energy from this identifiable “resonant” water waveis propor- be observed clearly fall in this saturated equilibrium region BAKRICK el a!. : SEA BACKSCATTER AT HF 675 for all operating frequencies above about 2-3 MHz. The fact be optimal, and hence most sea-echo data were recorded at that the first-order echoes at favorable ionospheric propaga- these ranges. At these ranges, the water depthexceeds 1000 ft, tion frequencies originate from wavesof known height charac- so that bottom effects on the wave characteristics are neg- teristics suggests that these echoes can be used as a standard ligible.
Load more

Recommended publications
  • Compact Bilateral Single Conductor Surface Wave Transmission Line
    Compact bilateral single conductor Regarded as half mode CPW, a series of slotlines have been proposed whose characteristic impedance is easy to control [7]. The bilateral surface wave transmission line slotline with 50 ohm characteristic impedance is designed as shown in Fig. 2. The copper layers on both sides of the substrate are connected by Zhixia Xu, Shunli Li, Hongxin Zhao, Leilei Liu and the metalized via arrays, and the two via arrays can increase the perunit- Xiaoxing Yin length capacitance and decrease characteristic impedance to 50 ohm which is usually quite high for a conventional slotline. The height of via A compact bilateral single conductor surface wave transmission line h is 1.524 mm, the slot S is 0.3 mm; the space between via arrays d is (TL) is proposed, converting the quasi-transverse electromagnetic 0.4 mm; the space between neighbour vias a is 1 mm. (QTEM) mode of low characteristic impedance slotline into the As a single conductor TL, bilateral corrugated metallic strips are transverse magnetic (TM) mode of single-conductor TL. The propagation constant of the proposed TL is decided by geometric printed on both sides of the substrate and connected by via arrays the parameters of the periodic corrugated structure. Compared to configuration is shown in Fig. 3a. To excite the transverse magnetic conventional transitions between coplanar waveguide (CPW) and (TM) mode, the surface mode of the corrugated strip, from the quasi- single-conductor TLs, such as Goubau line (G-Line) and surface transverse electromagnetic (QTEM) mode, the mode of slotline, we plasmons TL, the proposed structure halves the size and this feature propose a compact bilateral transition structure, as shown in Fig.
    [Show full text]
  • Radio Communications in the Digital Age
    Radio Communications In the Digital Age Volume 1 HF TECHNOLOGY Edition 2 First Edition: September 1996 Second Edition: October 2005 © Harris Corporation 2005 All rights reserved Library of Congress Catalog Card Number: 96-94476 Harris Corporation, RF Communications Division Radio Communications in the Digital Age Volume One: HF Technology, Edition 2 Printed in USA © 10/05 R.O. 10K B1006A All Harris RF Communications products and systems included herein are registered trademarks of the Harris Corporation. TABLE OF CONTENTS INTRODUCTION...............................................................................1 CHAPTER 1 PRINCIPLES OF RADIO COMMUNICATIONS .....................................6 CHAPTER 2 THE IONOSPHERE AND HF RADIO PROPAGATION..........................16 CHAPTER 3 ELEMENTS IN AN HF RADIO ..........................................................24 CHAPTER 4 NOISE AND INTERFERENCE............................................................36 CHAPTER 5 HF MODEMS .................................................................................40 CHAPTER 6 AUTOMATIC LINK ESTABLISHMENT (ALE) TECHNOLOGY...............48 CHAPTER 7 DIGITAL VOICE ..............................................................................55 CHAPTER 8 DATA SYSTEMS .............................................................................59 CHAPTER 9 SECURING COMMUNICATIONS.....................................................71 CHAPTER 10 FUTURE DIRECTIONS .....................................................................77 APPENDIX A STANDARDS
    [Show full text]
  • Long Earthquake'waves
    ~ LONG EARTHQUAKE'WAVES Seisllloloo-istsLl are tuning their instnlments to record earth 1l10tiollS with periods of one Jninute to an hour and mllplitudes of less than .01 inch. These,,~aycs tell llluch about the earth's crust and HHltltle by Jack Oliver "lhe hi-H enthusiast who hitS strug· per cycle. A reI.ltlvely shorr earthquake earth'luake waves tmvel at .9 to 1.S 1 gled to ImprO\'e tlIe re;pollse of wave has a duration of 10 seconds. At miles per second, they lange in length hI:; e'jlllpment In the bass range at present the most infornl.1tive long waves from 10 mile" up to the 8,OOO-mde length .11 oUlld 10 c~'d(-s per ;econd wIll ha VI" a h,\v€ periods of 15 to 75 seconds from of the earth's ,hamete... TheIr amplitude, fellow-feeling for the selsmologi;t \vho CfEst to crest. \Vith more advanced in­ however, is of an entirely di/lerent 01 de.. : IS ,attempting to tune hiS installments to ,,11 uments seismologists hope sooo to one of these waves displaces a point on the longest earth'luake \\".\\'es. But where study 450-second waves. The longest so the sudace of the eal th at some dislil1lce IIl-n deals in cITIes per second, seisll1OIo" f.tr detected had ., penod of :3,400 sec­ from the shock by no more than a hun· gy measures its fre<luencle; 111 seconds onds-·nearly an hour! Since these long dredth of an inch, even when eXCited by t/) ~ ~ SUBTERRANEAN TOPOGRAPHY of the North American con· at which the depth of the boundary was established.
    [Show full text]
  • Comparison of Available Methods for Predicting Medium Frequency Sky-Wave Field Strengths
    NTIA-Report-80-42 Comparison of Available Methods for Predicting Medium Frequency Sky-Wave Field Strengths Margo PoKempner us, DEPARTMENT OF COMMERCE Philip M. Klutznick, Secretary Henry Geller, Assistant Secretary for Communications and Information June 1980 I j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j TABLE OF CONTENTS Page LIST OF FIGURES iv LIST OF TABLES iv ABSTRACT 1 1. INTRODUCTION 1 2. CHRONOLOGICAL DEVELOPMENT OF MF FIELD-STRENGTH PREDICTION METHODS 2 3. DISCUSSION OF THE METHODS 4 3.1 Cairo Curves 4 3.2 The FCC Curves 7 3.3 Norton Method 10 3.4 EBU Method 11 3.5 Barghausen Method 12 3.6 Revision of EBU Method for the African LF/MF Broadcasting Conference 12 3.7 Olver Method 12 3.8 Knight Method 13 3.9 The CCIR Geneva 1974 Methods 13 3.10 Wang 1977 Method 15 3.11 The CCIR Kyoto 1978 Method 15 3.12 The Wang 1979 Method 16 4.
    [Show full text]
  • Surface Waves: What Are They? Why Are They Interesting?
    SURFACE WAVES: WHAT ARE THEY? WHY ARE THEY INTERESTING? Janice Hendry Roke Manor Research Limited, Old Salisbury Lane, Romsey, SO51 0ZN, UK [email protected] ABSTRACT Surface waves have been known about for many decades and quite in-depth research took place up until ~1960s . Since then, little work has been done in this area. It is unclear why, however today we have more powerful modelling methods which may enable us to understand their use better. It is known that high frequency (HF) surface waves follow the terrain and this has been utilised in some cases such as Raytheon's HF surface wave radar (HFSWR) for detecting ships over-the-horizon. It is thought with some more insight and knowledge of this phenomenon, surface waves could be extremely useful for both military and civil use, from communications to agriculture. WHAT ARE SURFACE WAVES? Over the many decades that surface waves have been researched, some confusion has built up over exactly what constitutes a surface wave. This was discussed by James Wait in an IEE Transaction in 1965 1 and was even a matter of discussion at the General Assembly of International Union of Radio Science (URSI) held in London in 1960. It was concluded that “there is no neat definition which would encompass all forms of wave which could glide or be guided along an interface”. However, the definitions which have been settled upon for this paper are as follows: Surface Wave Region : The region of interest in which the surface wave propagates. Surface Wave : A surface wave is one that propagates along an interface between two different media without radiation; such radiation being construed to mean energy converted from the surface wave field to some other form.
    [Show full text]
  • Reception of Skywave Signals Near a Coastline
    JOURNAL OF RESEARCH of the National Bureau of Standards-D. Radio Propagation Vol. 67D, No.3, May- June 1963 Reception of Skywave Signals Near a Coastline J. Bach Andersen Contribution from Laboratory of Electromagnetic Theory, The Technical University of Denmark, Copenhagen, Denmark (Recei\'ed November 5, 1962) An experimental investigation has been made on t he influence of gt'ou nd inhomoge­ neities on the reception of skywave sig nals, especiall y t he in fluence of the conductivity contrast ncar a coastline. This gives rise to a r apid decrease in fi eld strength ncar til(' coastline as is "'ell known from g roundwave mixed path theory. Comparison with Lheory is given. Infl uC'llce of dilhts(' reflection from t he ionosplwre is also cOIl :; idereri . 1. Introduction conditions, i. e., a s Lraight boundary lin e, n,lt <l IH1 homogeneo us sectiollS , it was co nsidered worthwhile ;,lany factors influence the radiation 01' reception to measure tbe field in tensity at a n actual reception of skywave signals in the shortw,we ra nge, a nd in site in order to find Lhe deviation s from the simple choosing a proper site for a HF-a ntenna it is impor­ theory. tant to evaluate the influence of the various factors. lnstead of m eftsuring t he verticlll radiation pat­ They include th e electrical parameters (the conduc­ tern aL d iIrerent distances from Lhe coastlin e, the tivity and the p ermi ttiv ity) of the groulld, hills, or fi eld intensity from a distf\nL Lran smitter was m eas­ clift's a nd other irregularities of the sbape of the ured simultaneo usly at two d ifr erent places.
    [Show full text]
  • Sky-Wave Propagation
    ANTENNA AND WAVE PROPAGATION Introduction Electromagnetic Wave(Radio Waves) travel with a vel. of light. These waves comprises of both Electric and Magnetic Field. The two fields are at right-angles to each other and the direction of propagation is at right-angles to both fields. The Plane of the Electric Field defines the Polarisation of the wave. Field Strength Relationship Electric Field, E x y Magnetic Direction of Field, H z Propagation Electromagnetic Wave(Radio Waves) travel with a vel. of light. These waves comprises of both Electric and Magnetic Field. The two fields are at right-angles to each other and the direction of propagation is at right-angles to both fields. The Plane of the Electric Field defines the Polarisation of the wave. POLARIZATION The polarization of an antenna is the orientation of the electric field with respect to the Earth's surface. Polarization of e.m. Wave is determined by the physical structure of the antenna and by its orientation. Radio waves from a vertical antenna will usually be vertically polarized. Radio waves from a horizontal antenna are usually horizontally polarized. Classification of Radio Wave Propagation GROUND WAVE, SPACE WAVE, SKY WAVE Ground Waves or Surface Waves Ground Waves or Surface Waves ◦ Frequencies up to 2 MHz ◦ follows the curvature of the earth and can travel at distances beyond the horizon (upto some km) ◦ must have vertically polarized antennas ◦ strongest at the low- and medium-frequency ranges ◦ AM broadcast signals are propagated primarily by ground waves during the day and by sky waves at nightis a Surface Wave that propagates or travels close to the surface of the Earth.
    [Show full text]
  • KHF 950/990 HF Communications Transceiver PILOT’S GUIDE and DIRECTORY of HF SERVICES
    KHF 950/990 HF Communications Transceiver PILOT’S GUIDE AND DIRECTORY OF HF SERVICES A Table of Contents INTRODUCTION KHF 950/990 COMMUNICATIONS TRANSCEIVER . .I SECTION I CHARACTERISTICS OF HF SSB WITH ALE . .1-1 ACRONYMS AND DEFINITIONS . .1-1 REFERENCES . .1-1 HF SSB COMMUNICATIONS . .1-1 FREQUENCY . .1-2 SKYWAVE PROPAGATION . .1-3 WHY SINGLE SIDEBAND IS IMPORTANT . .1-9 AMPLITUDE MODULATION (AM) . .1-9 SINGLE SIDEBAND OPERATION . .1-10 SINGLE SIDEBAND (SSB) . .1-10 SUPPRESSED CARRIER VS. REDUCED CARRIER . .1-10 SIMPLEX & SEMI-DUPLEX OPERATION . .1-11 AUTOMATIC LINK ESTABLISHMENT (ALE) . .1-11 FUNCTIONS OF HF RADIO AUTOMATION . .1-11 ALE ASSURES BEST COMM LINK AUTOMATICALLY . .1-12 SECTION II KHF 950/990 SYSTEM DESCRIPTION. .2-1 KCU 1051 CONTROL DISPLAY UNIT . .2-1 KFS 594 CONTROL DISPLAY UNIT . .2-3 KCU 951 CONTROL DISPLAY UNIT . .2-5 KHF 950 REMOTE UNITS . .2-6 KAC 952 POWER AMPLIFIER/ANT COUPLER .2-6 KTR 953 RECEIVER/EXITER . .2-7 ADDITIONAL KHF 950 INSTALLATION OPTIONS .2-8 SINGLE KHF 950 SYSTEM CONFIGURATION .2-9 KHF 990 REMOTE UNITS . .2-10 KAC 992 PROBE/ANTENNA COUPLER . .2-10 KTR 993 RECEIVER/EXITER . .2-11 SINGLE KHF 990 SYSTEM CONFIGURATION . .2-12 Rev. 0 Dec/96 KHF 950/990 Pilots Guide Toc-1 Table of Contents SECTION III OPERATING THE KHF 950/990 . .3-1 KHF 950/990 GENERAL OPERATING INFORMATION . .3-1 PREFLIGHT INSPECTION . .3-1 ANTENNA TUNING . .3-2 FAULT INDICATION . .3-2 TUNING FAULTS . .3-3 KHF 950/990 CONTROLS-GENERAL . .3-3 KCU 1051 CONTROL DISPLAY UNIT OPERATION .
    [Show full text]
  • Wireless Energy Harvesting by Direct Voltage Multiplication on Lateral Waves from a Suspended Dielectric Layer
    SPECIAL SECTION ON ENERGY EFFICIENT WIRELESS COMMUNICATIONS WITH ENERGY HARVESTING AND WIRELESS POWER TRANSFER Received September 2, 2017, accepted September 26, 2017, date of publication September 29, 2017, date of current version November 7, 2017. Digital Object Identifier 10.1109/ACCESS.2017.2757947 Wireless Energy Harvesting by Direct Voltage Multiplication on Lateral Waves From a Suspended Dielectric Layer LOUIS WY LIU 1, QINGFENG ZHANG 1, YIFAN CHEN2, MOHAMMED A. TEETI1, AND RANJAN DAS1,3 1Electrical and Electronics Engineering Department, Southern University of Science and Technology, Shenzhen 154108, China 2School of Engineering, University of Waikato, Hamilton 3240, New Zealand 3School of Engineering, IIT Bombay, Mumbai 400076, India Corresponding author: Qingfeng Zhang ([email protected]) This work was supported in part by the Guangdong Natural Science Funds for Distinguished Young Scholar under Grant 2015A030306032, in part by the Guangdong Special Support Program under Grant 2016TQ03X839, in part by the National Natural Science Foundation of China under Grant 61401191, in part by the Shenzhen Science and Technology Innovation Committee funds under Grant KQJSCX20160226193445, Grant JCYJ20150331101823678, Grant KQCX2015033110182368, Grant JCYJ20160301113918121, Grant JSGG20160427105120572, and in part by the Shenzhen Development and Reform Commission Funds under Grant [2015] 944. ABSTRACT This paper explores the feasibility of wireless energy harvesting by direct voltage multiplication on lateral waves. Whilst free space is undoubtedly a known medium for wireless energy harvesting, space waves are too attenuated to support realistic transmission of wireless energy. A layer of thin stratified dielectric material suspended in mid-air can form a substantially less attenuated pathway, which efficiently supports propagation of wireless energy in the form of lateral waves.
    [Show full text]
  • Radio Communication Via Near Vertical Incidence Skywave Propagation: an Overview
    Telecommun Syst DOI 10.1007/s11235-017-0287-2 Radio communication via Near Vertical Incidence Skywave propagation: an overview Ben A. Witvliet1,2 · Rosa Ma Alsina-Pagès3 © The Author(s) 2017. This article is published with open access at Springerlink.com Abstract Near Vertical Incidence Skywave (NVIS) propa- 1 Introduction gation can be used for radio communication in a large area (200km radius) without any intermediate man-made infras- Recently, interest in radio communication via Near Verti- tructure. It is therefore especially suited for disaster relief cal Incidence Skywave (NVIS) propagation has revived, not communication, communication in developing regions and in the least because of its role in emergency communica- applications where independence of local infrastructure is tions in large natural disasters that took place in the last desired, such as military applications. NVIS communication decade [1–3]. The NVIS propagation mechanism enables uses frequencies between approximately 3 and 10MHz. A communication in a large area without the need of a network comprehensive overview of NVIS research is given, cover- infrastructure, satellites or repeaters. This independence of ing propagation, antennas, diversity, modulation and coding. local infrastructure is essential for disaster relief communi- Both the bigger picture and the important details are given, cations, when the infrastructure is destroyed by a large scale as well as the relation between them. natural disaster, or in remote regions where this infrastructure is lacking. In military communications, where independence Keywords Radio communication · Emergency communi- of local infrastructure is equally important, communications cations · Radio wave propagation · Ionosphere · NVIS · via NVIS propagation have always remained important next Antennas · Diversity · Modulation to troposcatter and satellite links.
    [Show full text]
  • ULTRA WIDEBAND SURFACE WAVE COMMUNICATION J. A. Lacomb
    Progress In Electromagnetics Research C, Vol. 8, 95{105, 2009 ULTRA WIDEBAND SURFACE WAVE COMMUNICATION J. A. LaComb and P. M. Mileski Naval Undersea Warfare Center 1176 Howell St., Newport, RI 02841, USA R. F. Ingram Science Applications International Corporation (SAIC) 23 Clara Dr. Suite 206 Mystic, CT 06355, USA Abstract|Ultra Wideband (UWB), an impulse carrier waveform, was applied at HF-VHF frequencies to utilize surface wave propagation. Due to the low duty cycle of the pulse, the energy requirements are signi¯cantly reduced. UWB involves the propagation of transient pulses rather than continuous waves which makes the system easier to implement, inexpensive and small. The use of surface wave propagation (instead of commercial SHF UWB) extends the communication range. The waveform, transmitter, receiver, modulation and channel characteristics of the novel system design will be presented. 1. INTRODUCTION Ultra Wideband (UWB) technology is vastly di®erent from classical radio transmission. The extremely short pulses are generated at baseband and are transmitted without the use of a carrier. The short pulses of electromagnetic energy translate to very wide transmission bandwidths in the frequency domain. The Federal Communications Commission (FCC) de¯nes UWB as a signal with either a fractional bandwidth of 20% of the center frequency or 500 MHz. Due to the low duty cycle of the pulse the energy requirements are signi¯cantly reduced. Due to the low power spectral density the system has a low probability of intercept (LPI). Corresponding author: J. A. LaComb ([email protected]). 96 LaComb, Mileski, and Ingram The FCC has allocated 7,500 MHz of spectrum for unlicensed use of UWB in the 3.1 to 10.6 GHz frequency band [1].
    [Show full text]
  • High Frequency Surface Wave Radar
    Beyond the horizon: High Frequency Surface Wave Radar Frédéric Lamole1, François Jacquin1, Gilles Rigal2 1 Embedded Systems Dpt / HF division 5, rue Brindejonc des Moulinais, 31506 Toulouse Cedex 5 2 Embedded Systems Dpt / HF division Les Hauts de la Duranne, 370, rue René Descartes, 13857 Aix-en-Provence Cedex 3 ABSTRACT In this paper, we present a high-level view of the High Frequency Surface Wave Radar developed for the Radars for long distance maritime surveillance and SAR operations (RANGER) project ([1]). The over-the-horizon radar proposes a new system architecture, with new waveforms, new processing methods, and new antenna concepts to provide solutions to meet HFSWR (High Frequency Surface Wave Radar) challenges as increasing the long range distance detection for small vessels with improved accuracy. Keywords: Over-the-horizon (OTH) Radar; High Frequency (HF) Surface Wave Radar (SWR); maritime surveillance; Radar Cross Section (RCS) 1. INTRODUCTION The potential offered by HF surface wave radars for maritime surveillance and in particular for the entire Exclusive Economic Zone (EEZ), is a sea area for a state which has rights from its baseline out to 200 nautical miles from the coast defined by the United Nations Convention on the Law of the Sea in 1982[2], has recently been rediscovered, with the overhaul of national strategies related to security and surveillance of the maritime environment. Thus, over the past decade or so, the evolution of the strategic context has led to international instability, primarily affecting fragile states, promoting illicit and violent activities, generating potential risks for societies as: security threats, caused by trafficking (narcotics, psychotropic substances, weapons), illegal transport of migrants, maritime terrorism and piracy, have replaced the military threat.
    [Show full text]