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Active defense represents an innovative way of protecting military vehicles. It is based on the employment of a set of radar sensors which detect an approaching threat missile and activate a suitable counter-measure. Since the radar sensors are supposed to detect flying missiles very fast and, at the same time, distinguish them from stationary or slow-moving objects, CW Doppler radar sensors can be employed with a benefit. The submitted article deals with a complex noise analysis of this type of sensors. The analysis considers the noise of linear and quasi-linear RF components, phase-noise of the local oscillator as well as the noise of low-frequency circuits. Since the incidence of the phase-noise depends strongly upon the time delay between the reference and the cross-talked signals, a new method of measuring noise parameters utilizing a reflecting wall has been developed and verified. The achieved results confirm potentially high influence of the phase-noise on the noise parameters of the mentioned type of radar sensors. Obtained results can be used for the analysis of noise parameters of the similar but even more complex sensors.

International audience ; For obvious reasons of cost, discretion and reliability costs, locating and tracking aerial targets under an electromagnetically completely passive paradigm, relying exclusively on illuminators of opportunity, is very appealing for military but also civilian tasks. Such a passive radar system could exploit signals emitted by existing commercial television or radio stations or even satellite signals, such as the ones belonging to the GPS. This paper focuses on target locating and tracking using a network of passive receivers and/or non-cooperative illuminators, forming a multi-static radar configuration. The central idea is to make use of the bi-static Doppler shift. To make tracking possible, more than one bistatic Doppler shift has to be measured and the information combined. It is the purpose of the paper to describe this kind of technique and to present its main issues and workarounds, using a gradual approach. Conclusions and perspectives are drawn in the end.

International audience ; For obvious reasons of cost, discretion and reliability costs, locating and tracking aerial targets under an electromagnetically completely passive paradigm, relying exclusively on illuminators of opportunity, is very appealing for military but also civilian tasks. Such a passive radar system could exploit signals emitted by existing commercial television or radio stations or even satellite signals, such as the ones belonging to the GPS. This paper focuses on target locating and tracking using a network of passive receivers and/or non-cooperative illuminators, forming a multi-static radar configuration. The central idea is to make use of the bi-static Doppler shift. To make tracking possible, more than one bistatic Doppler shift has to be measured and the information combined. It is the purpose of the paper to describe this kind of technique and to present its main issues and workarounds, using a gradual approach. Conclusions and perspectives are drawn in the end.

Abstract. The article reports on the impact of the assimilation of wind vertical
profile data in a kilometre-scale NWP system on predicting heavy
precipitation events in the north-western Mediterranean area. The data
collected in diverse conditions by the airborne W-band radar RASTA (Radar
Airborne System Tool for Atmosphere) during a 45-day period are assimilated
in the 3 h 3DVAR assimilation system of AROME. The impact of the length of
the assimilation window is investigated. The data assimilation experiments
are performed for a heavy rainfall event, which occurred over south-eastern
France on 26 September 2012 (IOP7a) and over a 45-day cycled period. Results
indicate that the quality of the rainfall accumulation forecasts increases
with the length of the assimilation window, which recommends using
observations with a large period centred on the assimilation time. The
positive impact of the assimilation of RASTA wind data is particularly
evidenced for the IOP7a case since results indicate an improvement in the
predicted wind at short-term ranges (2 and 3 h) and in the 11 h
precipitation forecasts. However, in the 45-day cycled period, the comparison
against other assimilated observations shows an overall neutral impact.
Results are still encouraging since a slight positive improvement in the 5,
8 and 11 h precipitation forecasts was demonstrated.

Пропонується розробка авіаційної радіолокаційної системи з фазованою антеною решіткою повітряного базування військових літаків та вертольотів для попередження екіпажу про ракетну атаку наземних комплексів протиповітряної оборони противника. ; Предлагается разработка авиационной радиолокационной системы с фазированною антенной решёткой воздушного базирования военных самолетов и вертолетов для предупреждения экипажа о ракетной атаке наземных комплексов противовоздушной обороны противника. ; Antenna pattern, effective surface of dispersion, polarity, pulsewise - the Doppler radar-tracking system, the phased antenna array, military flight vehicles polarisation, electrical vector.

Introduction/purpose: This paper presents a model of a high speed target radar tracking system that is much simpler than the existing ones. The Doppler shift is compensated before signal compression, simultaneously with the modification of the clock signal in the compression filter. This is possible thanks to the development of FPGA technology. The most important for this application are very fast clock control units which enable operation with different frequency references up to 1 GHz with an accuracy far below 1 Hz. Methods: In this paper, the methodology of mathematical modeling and simulation is used. Results: The results of the analysis of the most important effects in radars caused by high-speed targets are presented and discussed - target migration through resolution cells and compression filter response distortion due to high target acceleration. Conclusion: Thanks to flexible RF and signal processing hardware, complex radar processing procedures are not required. The sensitivity of the BPSK signal to the Doppler shift (which is usually considered a disadvantage) can be used to reject targets at a slightly different rate. This system can be used in space debris tracking, airspace target tracking, car driving, etc.

Doppler radar installation by the National Weather Service (NWS) improved tornado warning performance, raising the probability of detection and mean lead time while reducing the false alarm ratio. Research on tornado casualties has established that a warning reduces tornado injuries while lead times of up to fifteen minutes also reduce tornado fatalities. In this paper we estimate the decrease in tornado casualties attributable to the observed change in the distribution of warning lead times, and thus provide evidence on the benefit to society of weather warning systems. We find that increases in warning lead times accounts for 30–50 percent of the reduction in injuries but no more than 1/4 of the reduction in fatalities which occurred with the installation of Doppler radar by the NWS. Future improvements in warning performance to further reduce tornado fatalities by 18 percent and injuries by 24 percent.

1 Elementary Electromagnetics and the Radar Range Equation -- Radio Waves -- A Simple Radar -- The Radar Range Equation -- Surveillance -- Tracking -- Exercises -- References -- 2 Antennas -- A Parabolic Reflector -- The Antenna Pattern -- The Interferometer -- Finding Sidelobe Levels -- Array Radars -- Element Spacing -- Array Gain -- Array Thinning -- Array Design Considerations -- Exercises -- References -- 3 Detection and Tracking -- The Problem of Detection -- Noise Distributions -- Signal-to-Noise Ratio -- Designing Thresholds -- Some Detection Techniques -- Tracking -- Exercises -- References -- 4 Radar Cross Section -- RCS of a Sphere -- RCSs of Simple Objects -- Polarization -- Chaff Characteristics -- Diffuse Targets and Clutter -- Radar Signatures -- Exercises -- References -- 5 Waveforms and Signal Processing -- Characteristics of the Simple Pulse -- Range Measurement -- Doppler Measurements -- Pulse Compression -- Time Sidelobes -- Pulse Burst Waveforms -- Ambiguity Functions -- Signal Processing -- Exercises -- References -- 6 Electronic Countermeasures (ECM) -- Mainbeam Jamming -- Sidelobe Jamming -- Low-Probability-of-Intercept Radar (LPIR) -- Other Jamming Techniques -- Passive ECM -- Exercises -- References -- 7 Systems Applications -- Over-the-Horizon Radars -- Radar Altimeters -- Ionospheric Radars -- Advanced Technology Radars -- Pulse-Doppler Radars -- Synthetic Aperture Radar -- Laser Radars -- Exercises -- References -- 8 Loose Ends of Radar Lore -- Radar Horizon -- Properties of the Medium -- Ionosphere -- Troposphere -- Far Field of an Antenna -- Convenient Radar Rules of Thumb -- Exercises -- References -- 9 Radar Potentials and Limitations -- Surveillance -- Navigation -- Signatures -- Science -- Summary -- Appendix 1 Conversion to Decibels -- Appendix 2 The Electromagnetic Spectrum -- Appendix 3 Fourier Series and Transforms -- Fourier Series -- Fourier Transforms -- Appendix 4 Answers to Exercises -- Appendix 5 Glossary.

This work develops an algorithm to retrieve the vertical structure of the raindrop size distribution (DSD) of rain from simultaneous observations of 47 MHz Equatorial Atmosphere Radar (EAR) and 1.3 GHz Boundary Layer Radar (BLR) at Koto Tabang, West Sumatra, Indonesia (0.20°S, 100.32°E, 865 m above sea level). EAR is sensitive to the detection of turbulence, and BLR is susceptible to identifying precipitation echo. The EAR Doppler spectrum broadening effects due to turbulence and finite radar beam width were reduced using the convolution process. The Gaussian function was used to model the turbulence Doppler spectrum. A non-linear least-squares fitting method was applied to retrieve DSD parameters. Subsequently, the equations to estimate DSD using this dual-frequency algorithm assume the gamma DSD model to retrieve the distribution from the Doppler spectrum of precipitation echo. The precipitation events on April 23, 2004 on the Coupling Processes in the Equatorial Atmosphere (CPEA-I) project have been analyzed. Results show that the precipitation spectrum obtained using the dual-frequency method is higher, more precise, and well-fitted than the single-frequency method, meaning the dual-frequency method has great potential to be used in observing the microphysical process and remote sensing application analysis of DSD in Indonesia, particularly at Koto Tabang. The analyses show various microphysical processes that occur in the rain, such as coalescence, evaporation, break-up, and condensation. Furthermore, for the purpose of easier remote sensing application analysis of profile DSD characteristics, we use a DSD ΔΖMP parameter. ΔΖMP is a rain rate insensitive DSD parameter representing mean drop size. The trend of ΔZMP is not totally uniform with regards to rain rate and reflectivity factors, with ΔZMP higher in the first half of the event and becoming lower toward the end. This suggests that we have to use different Z-R relations within the event. Doi: 10.28991/ESJ-2022-06-03-02 Full Text: PDF

Abstract. Weather radar observations are currently the most reliable method for remote sensing of precipitation. However, a number of factors affect the quality of radar observations and may limit seriously automated quantitative applications of radar precipitation estimates such as those required in Numerical Weather Prediction (NWP) data assimilation or in hydrological models. In this paper, a technique to correct two different problems typically present in radar data is presented and evaluated. The aspects dealt with are non-precipitating echoes – caused either by permanent ground clutter or by anomalous propagation of the radar beam (anaprop echoes) – and also topographical beam blockage. The correction technique is based in the computation of realistic beam propagation trajectories based upon recent radiosonde observations instead of assuming standard radio propagation conditions. The correction consists of three different steps: 1) calculation of a Dynamic Elevation Map which provides the minimum clutter-free antenna elevation for each pixel within the radar coverage; 2) correction for residual anaprop, checking the vertical reflectivity gradients within the radar volume; and 3) topographical beam blockage estimation and correction using a geometric optics approach. The technique is evaluated with four case studies in the region of the Po Valley (N Italy) using a C-band Doppler radar and a network of raingauges providing hourly precipitation measurements. The case studies cover different seasons, different radio propagation conditions and also stratiform and convective precipitation type events. After applying the proposed correction, a comparison of the radar precipitation estimates with raingauges indicates a general reduction in both the root mean squared error and the fractional error variance indicating the efficiency and robustness of the procedure. Moreover, the technique presented is not computationally expensive so it seems well suited to be implemented in an operational environment.

Active electronically scanned antenna (AESA)-based radars imbibe the desirable feature of 'graceful degradation'. Such radars use miniaturised transmit-receive (TR) modules and a failure of few modules does not lead to failure of the mission. For example, in AESA-based ground MTI radar, failure of a few modules does not affect the array performance. In such a case, the static ground clutter is centred on zero frequency does not have a motion dependent Doppler spread. However, in airborne AESA radars, the ground clutter has an angle dependent Doppler frequency due to the platform motion and clutter leaking in through antenna side-lobes. Hence, the antenna side lobe levels dictate the side lobe clutter against which target detection is to be performed. The detection performance is governed by the signal to interference plus noise ratio (SINR). For Airborne surveillance radar the effect of random and systematic failures of TR modules and their effect on SINR is characterised. It is shown that single channel processing does not effectively provide the graceful degradation feature as the SINR loss due to failures is significant. However, the effect of systematic failure on SINR loss is less as compared to random failures. An effective scheme for feeding the array is also proposed.

"This book focuses on airborne radar system, radar detection enhancement, airborne self-deception jammer and spoofing. It presents the fundamentals of airborne radar, radar detection methods, space time adaptive processing STAP, jamming and spoofing fundamentals, jamming and spoofing methods, deception jamming, and Doppler effects. It outlines the radar platform and system modeling, target modeling, clutter modeling, jamming modeling"--

In 1998, the Naval Postgraduate School (NPS) Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) and the NPS Department of Electrical and Computer Engineering (ECE Dept.) collaborated on the acquisition of a mobile radar, the AN/MPQ-64 (Sentinel). This is a modern X-band, pulse Doppler radar used by the Army for forward area air defense. An SBIR project funded by the Office of Naval Research resulted in a contract to ProSensing, Inc., Amherst, MA to retrofit this radar with a weather processor. The intent is to provide a military capability to assess battlespace weather in real time. This capability will be developed using the NPS radar as a testbed. When the weather capability has been fully implemented on the NPS radar, it will also have application as a scientific instrument for severe storm research because of its mobility and cutting-edge capabilities. The modified radar has been designated the MWR-05XP (Mobile Weather Radar, 2005, X-band, Phased Array). This report presents the results of an analysis of numerous aspects of the radar's performance as a weather sensor. The ability of the MWR-05XP radar to detect rain with different levels of reflectivity, the ability of the radar to detect clear air turbulence with different structure parameters and echoes from birds and insects has been examined. Curves are provided to determine correlation and decorrelation times for weather signals with varying rms velocity spread. MWR-05XP post detection integration improvement has been computed for a Rayleigh weather target with varying pulse-to-pulse correlation and curves are provided to determine the improvement in terms of the number of pulses integrated. Lastly, scan strategy is discussed with emphasis on obtaining weather signal parameter estimates with small variance while at the same time achieving a rapid volumetric update rate. Electronic scan is the feature that enables the radar to achieve a rapid volumetric update rate. Data quality control is also discussed. ; Approved for public release; distribution is unlimited.

A ¨RADAR¨ system, from the English Acronym ¨Radio Detention and Ranging¨. Better known as ¨Radio Detection and Location¨ RDL. It is a system for detecting and positioning objects through shipping and reflection of electromagnetic waves in terms of the time of issue and the return of the waves and their speed (calculated by the Doppler effect of the electromagnetic signal received). Meanwhile, an autonomous unmanned vehicle, also known as Unmanned Aerial Vehicle, UAV, which is defined as an aircraft which does not carry a human operator, and uses aerodynamic forces to provide airlift by itself. Therefore, it can fly autonomously or it can be operated by remote control. This article focuses on the review of experiences where these two technologies are integrated, particularly UAVSAR (Uninhabited Aerial Vehicle Synthetic Aperture Radar). This is done in order to support research concerning the combination thereof to be applied in georeferencing humanitarian missions or military missions that require monitoring of airspace. ; Un sistema RADAR -del acrónimo en inglés ¨Radio Detention and Ranging¨, es decir, ¨Detección y Localización por Radio¨, es un sistema de detección y posicionamiento de objetos a través de envío y reflexión de ondas electromagnéticas en términos del tiempo de emisión y regreso de las ondas así como de su velocidad calculada mediante el efecto Doppler de la señal electromagnética recibida. En tanto, un vehículo autónomo no tripulado -cuyo nombre oficial es Unmanned Aerial Vehicle (UAV), se define como un vehículo motorizado aéreo que no lleva un operador humano, y utiliza las fuerzas aerodinámicas para proporcionar la elevación del mismo: es decir, puede volar de forma autónoma o ser dirigido por control remoto. El presente artículo se centra en la revisión de experiencias donde se integran estas dos tecnologías -particularmente la UAVSAR (Vehículos aéreos no tripulados con sistema RADAR de apertura sintética)-, con el fin de soportar investigaciones referentes a la combinación de las mismas para ...