Effect of horizontal gradients on ionospherically reflected or transionospheric paths using a precise homing-in method

The high-frequency hybrid sky-surface wave radar (HF HSSWR) has recently been used to monitor large-area sea states. However, most of the HF HSSWR detection methods are based on the assumption of a no-tilt and constant height ionospheric model, and the influences caused by uneven electron density are ignored. This paper proposes a new surface current inversion scheme for the HF distributed HSSWR system, which considers the unknown ionospheric state as a black box and extracts the key parameters to compute the surface current based on a scattering model. The computational formula of the component of the current vector is explored using spatial scattering theory instead of an approximate bistatic model. In addition, the Fourier series expansion method is applied to the HF data to extract the real first-order Bragg frequency. Subsequently, the grazing angle and the bistatic angle can be found by inversion using the first-order Bragg frequency formula after searching out the common scattering patch of two receiving stations. Simultaneously, the coordinate registration of the currents can also be determined. The feasibility and effectiveness of this new algorithm are verified with field experimental results by comparing the current vectors derived from HSSWR and traditional HF SWR. The RMS differences of the magnitude and direction of the current vectors within the core common area of the two detection systems are about 10.2 cm/s and 9.5°, respectively.

Ocean Surface Current Extraction Scheme With High-Frequency Distributed Hybrid Sky-Surface Wave Radar System

The performance of the high-frequency hybrid sky-surface wave radar is often degraded due to the distortion of radar echoes induced by time-varying ionosphere. Here a modified S-transform method based on the direct wave for ionosphere decontamination of high-frequency hybrid sky-surface wave radar is presented. First, we extract the time-varying-ionosphere-distorted phase of the echoes from the direct wave of high-frequency hybrid sky-surface wave radar by using the modified S-transform. Then this phase function is used to decontaminate the ionosphere distortion of radar echo at each range bins. Simulations and experimental data are conducted to validate the performance of the proposed method on decontaminating the distortion. The experimental data are acquired by Wuhan Universitys ocean state measuring and analyzing radar. A mass of radar data is processed and analyzed, demonstrating that the decontamination effect is statistically significant. The method is not only effective to remove the Doppler shift of direct wave and Bragg peaks caused by ionosphere but also able to narrow the broadened direct wave and Bragg peaks. Meanwhile, the SNR is improved in most range bins; the background noise is reduced detectably, sometimes significantly; and some isolated radar echoes near direct wave or Bragg peaks are recovered or enhanced. These results indicate that the proposed decontamination algorithm works well.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018RS006645

Correction of Ionospheric Distortion on HF Hybrid Sky-Surface Wave Radar Calibrated by Direct Wave

Dans ce memoire sont resumes mes travaux de recherche dans le domaine de la caracterisation large bande de frequence Apres une presentation des techniques large bande, deux applications sont decrites : le cas du radar pour l'etude de la SER de cibles aeriennes en vue de leur identification, et le cas des systemes de radiocommunications, l'etude et la modelisation du canal de propagation Ce memoire se decompose donc en deux parties principales La premiere est consacree au developpement de systemes radars HF – VHF a large bande de frequence et a diversite de polarisation pour la classification et l'identification de cibles aeriennes Deux approches sont etudiees, une multifrequence et l'autre a balayage de frequence Dans un premier temps, les systemes utilisant ces techniques, ainsi que leurs performances, sont decrits Des exemples de mesures de SER d'avions non cooperatifs sont presentes Les methodes d'identification de cibles reposent generalement sur la comparaison de mesures a une base de donnees Dans un second temps, les methodes numeriques utilisees pour la simulation de SER sont decrites et analysees Dans un troisieme temps, les methodes d'identification developpees sont presentees, discutees et illustrees par des resultats d'identification sur des cibles reelles Dans la deuxieme partie sont regroupes mes travaux sur la caracterisation large bande de frequence et la modelisation du canal de propagation Les differents chapitres de cette partie s'organisent en fonction de la frequence On trouve tout d'abord la bande HF dans laquelle un modele de previsions de propagation a ete developpe afin d'evaluer le comportement large bande du canal Differentes applications, telles que la reactualisation et la localisation a station unique, illustrent cette partie Dans la bande UHF, des travaux ont ete menes sur la caracterisation du canal de propagation radio-mobile et le developpement de nouveaux outils de sondage Des campagnes de mesures ont ete menees a l'aide d'un sondeur a correlation glissante SIMO (Single Input – Multiple Output) en milieu urbain La technique de mesure par balayage de frequence a aussi ete etudiee par le developpement d'un nouveau sondeur, l'objectif etant de realiser un equipement MIMO (Multiple Input – Multiple Output) permettant la mesure simultanee de tous les canaux de propagation Dans la bande EHF, le canal etudie concerne les applications des radars dans le domaine de l'automobile Des mesures ont ete realisees et un modele de propagation en est deduit La caracterisation du canal s'est appuyee sur un analyseur de reseau vectoriel La methodologie est explicitee et des comparaisons entre les simulations et les mesures sont presentees La derniere partie conclut en effectuant un bilan provisoire de mes activites et en presentant les perspectives de mon travail sur la caracterisation a large bande de frequence dans le domaine du radar et du sondage de canal Enfin, une liste des mes publications, des differents encadrements, des contrats de recherche sur lesquels j'ai travaille, de mes activites pedagogiques et administratives et des fonctions electives et autres responsabilites, est donnee

Caracterisation large bande de frequence : application au radar et au sondage de canal

[1] Estimation of arrival angles and incoming signals is a challenging problem for HF channels where the signals are correlated and the separation between the signals can be as low as a couple of degrees In this paper, a new algorithm, Multipath Separation-Direction of Arrival (MS-DOA), is developed to estimate both the arrival angles in elevation and azimuth and the incoming signals at the output of the reference antenna with very high accuracy The MS-DOA algorithm provides reliable angle and signal estimates even with small separation of arrival angles and for low SNRs The minimum number of antennas that are required by the algorithm is only one more than the number of incoming signals In a narrowed down region of interest and for a few incoming signals, the computational search time for MS-DOA is only a couple of minutes in a standard PC

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002RS002606

Mode separation and direction of arrival estimation in HF links

We examine the effects of tilts in the reflecting layers, by using measurements of angles of arrival on radio circuits. A simple mathematical method. Is used to establish the relationships between angle deviation, electron density gradient, frequency and transmitter-receiver range. We analyse the first results from a number of different transmission paths, and compare them with an average ionospheric model. Finally, we present a statistical study of the relative measurements of the two propagation modes (ordinary "O" and extraordinary "X") on one type of link. >

http://ieeexplore.ieee.org/iel3/1166/7915/00337017.pdf

First analysis of ionospheric tilts and their effects observed with a HF goniopolarimeter

The purpose of this paper is to present the phase and amplitude characteristics of an active loop antenna, which can be easily fitted into a polarization diversity sensor built with two crossed loops. We shall first consider the determination of the intrinsic complex effective height of the loop, taking into account the propagation effects of an incoming wave from the ionosphere. The antenna aerials are connected to preamplifiers which increase effective height, and also match them to the rest of the measurement system. In a second part, we show how the complex effective height is modified after passage through the preamplifier. These developments are illustrated by experimental measurements which take into account of the phase and amplitude of several incoming HF skywaves, identified by their direction of arrival and polarization. Finally, the performances in terms of antenna factor, of a small active circular loop antenna (radius 0.65 meters) are compared with those of an eight meter high passive biconical antenna.

D. Lemur

Papers

First analysis of ionospheric tilts and their effects observed with a HF goniopolarimeter

HF active loop antenna response