Short-Wavelength Technology and the Potential For Distributed Networks of Small Radar Systems

David McLaughlin, David Pepyne, Brenda Philips, James Kurose, Michael Zink, David Westbrook, Eric Lyons, Eric Knapp, Anthony Hopf, Alfred Defonzo, Robert Contreras, Theodore Djaferis, Edin Insanic, Stephen Frasier, V. Chandrasekar, Francesc Junyent, Nitin Bharadwaj, Yanting Wang, Yuxiang Liu, Brenda Dolan, Kelvin Droegemeier, Jerald Brotzge, Ming Xue, Kevin Kloesel, Keith Brewster, Frederick Carr, Sandra Cruz-Pol, Kurt Hondl, and Pavlos Kollias, 2009: Short-Wavelength Technology and the Potential For Distributed Networks of Small Radar Systems. Bull. Amer. Meteor. Soc., 90, 1797–1817. doi: http://dx.doi.org/10.1175/2009BAMS2507.1 -
http://journals.ametsoc.org/doi/abs/10.1175/2009BAMS2507.1

Flow diagram depicting the major processing steps of the closed-loop software architecture

Abstract. Dense networks of short-range radars capable of mapping storms and detecting atmospheric hazards are described. Composed of small X-band (9.4 GHz) radars spaced tens of kilometers apart, these networks defeat the Earth curvature blockage that limits today's long-range weather radars and enables observing capabilities fundamentally beyond the operational state-of-the-art radars. These capabilities include multiple Doppler observations for mapping horizontal wind vectors, subkilometer spatial resolution, and rapid-update (tens of seconds) observations extending from the boundary layer up to the tops of storms. The small physical size and low-power design of these radars permits the consideration of commercial electronic manufacturing approaches and radar installation on rooftops, communications towers, and other infrastructure elements, leading to cost-effective network deployments. The networks can be architected in such a way that the sampling strategy dynamically responds to changing weather to simultaneously accommodate the data needs of multiple types of end users. Such networks have the potential to supplement, or replace, the physically large long-range civil infrastructure radars in use today.

AN/TPS-59 radar

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Abandoned Radar Station - RAF Stenigot, Lincolnshire, England

After the invention of radar in the late 1930s, the UK built a string of early-detection systems along its coastline. A major hub in this "Chain Home" was the RAF Stenigot, in Lincolnshire. In the 1950s, the station was updated with tropospheric scatter dishes, which allowed the army to transit and receive microwave signals by beaming them through the troposphere-the lowest level of the Earth's atmosphere. They were eventually decommissioned in the 1980s, and today the abandoned dishes are used for everything from climbing to skateboarding.

Photo: DigiTaL~NomAd

Concrete Ears - WWII acoustic listening devices

Somewhere in Kent

Photos by Peter Pearson

US Navy Awards $217m Radar Contract to Raytheon

The US Navy has awarded a $217m contract to Raytheon to provide two volume search radar (VSR) arrays for the Zumwalt Class destroyer programme and the USS Gerald R Ford (CVN 78).

The architecture of the navy's dual-band radar (DBR) allows automatic operation with minimal human intervention and the integration of the S-band VSR radar arrays with SPY-3 X-band multi-function radar capabilities enhances the technology.

DBR is now under testing at the navy's engineering test centre in Virginia.

Under this contract the company will secure materials for the VSR as well as manufacture, test and deliver the radar system for the CVN 78 to support carrier air operations.

A second VSR unit for the Zumwalt Class destroyer programme will also be included in the contract.

The workplaces will be Raytheon's Surveillance and Sensor Center in Massachusetts and Lockheed Martin in New Jersey.

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Приемная радиолокационная станция РЛС Даугава

В середине 50-х годов была начата работа по созданию системы предупреждения ракетного нападения. Уже существовавшие на тот момент отдельные радиолокационные станции должны были объединиться в комплексы, из которых в дальнейшем комплектовались радиолокационные узлы.

Входящие в состав системы ракетно-космической обороны средства представляют собой сложные программно-аппаратные комплексы, обеспечиваемые инженерной поддержкой: конструкторы и инженеры постоянно стремятся к усовершенствованию систем обеспечения бесперебойного функционирования всех составляющих оборонного комплекса. В ходе этих работ решается ряд проблем научно-технического и производственного плана, что в итоге приводит к появлению усовершенствованной техники. Так, на основе центральной станции обнаружения баллистических объектов (ЦСО-П), работающей в метровом диапазоне, была разработана РЛС дальнего обнаружения типа «Дунай» с дальностью обнаружения объектов на расстоянии до 1 200 км, а созданная позже принципиально новая РЛС типа «Днестр» впоследствии была модифицирована до РЛС типа «Днепр».

Приемная радиолокационная станция (ПРЛС) «Даугава» создавалась в 1977 году как прототип РЛС нового типа «Дарьял». Ее антенна была в два раза меньше, чем у станции «Дарьял», но принимающая аппаратура, как и вычислительный комплекс, были оставлены без изменений. В этой станции была впервые применена гибридная СВЧ-технология, а также крупно-апертурные фазированные антенные решетки с фазовым управлением.

В 1978 году станция «Даугава» была установлена в Оленегорске в качестве дополнения к РЛС «Днепр», за счет чего была повышена устойчивость к помехам, вызываемым полярными сияниями, а также улучшило качество получаемой и обрабатываемой информации.

Впоследствии на базе РЛС Даугава и «Днепр» была создана станция нового поколения «Дарьял». Принимающая часть станции «Дарьял», размещенной в Мурманске, носила название «Даугава». Дальнейшая работа над проектом «Дарьял» привела к возникновению модификаций «Дарьял-У» и «Дарьял-УМ», по всем техническим характеристикам превышающих свой прототип - РЛС «Даугава».

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AN/MPQ-50 Photo gallery

An early production KJ-2000 Airborne Early Warning and Control system on short finals

KJ-200 AEW&C system in flight

EDA Approves Next-Gen Space-Based Military Surveillance System

The European Defence Agency (EDA) has agreed to approve a project for the next generation of European military earth observation satellites.

The multinational space-based imaging system (MUSIS) project has been launched by six European Union Member States: Belgium, Germany, Greece, France, Italy and Spain.

The MUSIS project aims at establishing a multinational space-based imaging system for surveillance, reconnaissance and observation to ensure continuity of services from the current French Helios II, German SAR LUPE and Italian Cosmo-Skymed and Pléiades systems, from 2015-2017 onwards.

EDA Head, Javier Solana said that he welcomed the initiative of the EU member states in approving this critical capability.

"Space-based related assets are critical to improve European military capabilities, including for information gathering," Solana said.

EDA's chief executive, Alexander Weis said that the EDA was proving its value by bringing together member states as well as by connecting military to civil space agendas.

"We will liaise with the commission and the European Space Agency to ensure complementing research and technology, and to seek other synergies," said Weis.

One of the roles for EDA will be to seek synergies with earth observation programmes on the civilian side, in particular with the global monitoring for environment and security (GMES) programme of the European Commission.

By Daniel Garrun.

RONSARD Radar: Implementation of Dual Polarization on a C-Band Doppler Weather Radar

The French C-band meteorological Doppler radar Recherche sur les Orages et Nuages par un Systeme Associe de Radars Doppler (RONSARD) was recently equipped with dual polarization. This modification required, on the one hand, an additional receiver and, on the other hand, a new design for the antenna geometry in order to decrease strongly the sidelobe level. This new radar configuration allows us to choose between two complementary modes: (1) the previous single-polarization mode, still preserved with fast Fourier transform calculations of the first three momentums of the Doppler spectrum, i.e., horizontal (H) reflectivity, radial wind velocity, and wind velocity variance calculated both in precipitation areas and clear air areas (depending on the gate), and (2) the dual-polarization mode with pulse pair processing of H and vertical reflectivities and velocities, differential phase shift, and coherence coefficient. Moreover, both modes work over contiguous gates along each direction, allowing fine radial range resolution. Thanks to the flexibility between these two modes, the RONSARD radar becomes a new major facility aimed at studying the dynamics-microphysics interactions within precipitation and their environment. - Reference

Statistical analysis of the zero-phase method for aligning noisy high-resolution radar signals

Automatic target recognition using high-range resolution radars is a difficult task. Variations in the distance to the target cause circular shifts of the received signal, and most of the classification algorithms are very sensitive to shifts over the input signal. This fact makes the alignment of each signal prior to any classification stage very important. Here the alignment of noisy signals using the zero phase method is studied. In order to evaluate the performance of the alignment method, a theoretical analysis of the sensitivity to noise of this alignment method is carried out. As a result, an analytical expression that predicts the error of the alignment method is obtained. The validity of this expression is also confirmed by experimental results. A database of high-range resolution radar profiles containing patterns belonging to six different targets has been used, and a comparative study of the sensitivity to noise estimated using the profiles of the database and predicted by the analytical expression is carried out. The results demonstrate that the proposed analytical expression is useful to analyse the sensitivity to noise of the zero-phase alignment method for medium and high signal-to-noise ratio values. - Reference

Discrete frequency-coded radar signal design

A modified simulated annealing algorithm (MSAA) is proposed as combinatorial multivariable optimisation technique to design discrete frequency-coding (DFC) sequence sets with good auto- and cross-correlation properties. The proposed algorithm is a combination of simulated annealing and Hamming scan algorithm. MSAA has global minimum estimation capability of simulated annealing and fast convergence rate of Hamming scan algorithm. Some of the synthesised results are presented, the properties of the sequence sets are shown to be better than the other sequence sets known in the literature. Synthesised DFC sequence sets have properties far better than polyphase sequence sets. The synthesised DFC sequence sets are promising for practical application to netted radar/multiple radar systems. - Reference

Three uncertainty relations for real signals associated with linear canonical transform

Uncertainty principle plays an important role in signal processing, physics and mathematics, and it represents the relations between time spread and frequency spread (or position and velocity). Linear canonical transform (LCT) is one generalisation of Fresnel transform, fractional Fourier transform and others. The LCT has been used in physical optics and signal processing. Three novel results of uncertainty principle in the LCT domains are obtained here, in which one is connected with parameters a and b and the other one is connected with c and d; the last one is connected with the four transformation parameters a, b, c and d. Their physical meanings are given as well. These results disclose the inequalities¿ relations between two spreads, between two group delays and between one spread and one group delay in the LCT domains. It also shows that any one of the three cases can reduce to classical uncertainty principle in time/frequency domain. The effects of time scaling on these results; bounds are also involved. - Reference

Composite spectrogram using multiple Fourier transforms

The authors propose a time-frequency (T-F) analysis method that uses a time- and frequencydependent resolution to represent a signal. The method is based on the idea of splitting the T-F plane into equal-TF-area Heisenberg boxes in some optimal way that closely matches spectral events. Compared with existing methods based on orthogonal decompositions, by lifting the orthogonality constraint, extra freedom is gained in the way the T-F plane can be partitioned, which enables time and frequency adaptation at the same time. A best tiling selection algorithm of quadratic complexity is derived using dynamic programming to find the optimal frame from a family. Experiments show the advantage of this more flexible representation. - Reference

A Polarimetric Radar Forward Operator for Model Evaluation

A polarimetric radar forward operator has been developed as a tool for the systematic evaluation of microphysical parameterization schemes in high-resolution numerical weather prediction (NWP) models. The application of such a forward operator allows a direct comparison of the model simulations to polarimetric radar observations. While the comparison of observed and synthetic reflectivity gives information on the quality of quantitative precipitation forecasts, the information from the polarimetric quantities allows for a direct evaluation of the capacity of the NWP model to realistically describe the processes involved in the formation and interactions of the hydrometeors and, hence, the performance of the microphysical parameterization scheme. This information is expected to be valuable for detecting systematic model errors and hence improve model physics. This paper summarizes the technical characteristics of the synthetic polarimetric radar (SynPolRad). Different polarimetric radar quantities are computed from model forecasts using a T-matrix scattering code and ice phase hydrometeors are explicitly considered. To do so, the sensitivities of the scattering processes to the microphysical characteristics of different ice hydrometeors are investigated using sensitivity studies. Furthermore, beam propagation effects are considered, including attenuation and beam bending. The performance of SynPolRad and the consistence of the assumptions made in the derivation of the input parameters are illustrated in a case study. The resulting synthetic quantities as well as hydrometeor classification are compared with observations and are shown to be consistent with the model assumptions.- Reference

An Analysis of Errors in Drop Size Distribution Retrievals and Rain Bulk Parameters with a UHF Wind Profiling Radar and a Two-Dimensional Video Disdrometer

Vertically pointed wind profiling radars can be used to obtain measurements of the underlying drop size distribution (DSD) for a rain event by means of the Doppler velocity spectrum. Precipitation parameters such as rainfall rate, radar reflectivity factor, liquid water content, mass-weighted mean drop diameter, and median volume drop diameter can then be calculated from the retrieved DSD. The DSD retrieval process is complicated by the presence of atmospheric turbulence, vertical ambient air motion, selection of fall speed relationships, and velocity thresholding. In this note, error analysis is presented to quantify the effect of each of those factors on rainfall rate. The error analysis results are then applied to two precipitation events to better interpret the rainfall-rate retrievals.

It was found that a large source of error in rain rate is due to unaccounted-for vertical air motion. For example, in stratiform rain with a rainfall rate of R = 10 mm h⁻¹, a mesoscale downdraft of 0.6 m s⁻¹ can result in a 34% underestimation of the estimated value of R. The fall speed relationship selection and source of air density information both caused negligible errors. Errors due to velocity thresholding become more important in the presence of significant contamination near 0 m s⁻¹, such as ground clutter. If particles having an equivalent volume diameter of 0.8 mm and smaller are rejected, rainfall rate errors from −4% to −10% are possible, although these estimates depend on DSD and rainfall rate.- Reference

Coupled Contributions in the Doppler Radar Spectrum Width Equation

Contrary to accepted usage, the second central moment of the Doppler spectrum is not the sum of the second central moments of individual spectral broadening mechanisms. A rigorous theoretical derivation of the spectrum width observed with short dwell times reveals that the sum cannot strictly be taken for the variances associated with various spectral broadening mechanisms and that an added-term coupling shear with turbulence is needed. Furthermore, shear and antenna rotation are coupled. The theoretical expressions derived herein apply to radars with fixed or scanning beams.- Reference

Clutter Suppression for Staggered PRT Waveforms

This paper presents a clutter suppression methodology for staggered pulse repetition time (PRT) observations. It is shown that spectral moments of precipitation echoes can be accurately estimated even in cases where clutter-to-signal ratios are high by using a parametric time domain method (PTDM).

Based on radar signal simulations, the accuracy of the proposed method is evaluated for various observation conditions. The performance of PTDM is demonstrated by the implementation of the staggered PRT at the Colorado State University–University of Chicago–Illinois State Water Survey (CSU–CHILL). Based on this study, it is found that the accuracy of the retrieval is comparable to the current state of the art methods applied to the uniformly sampled observations and that the estimated velocity is unbiased for the complete Nyquist range.- Reference

Effects of Multiple Scattering on Attenuation-Based Retrievals of Stratiform Rainfall from CloudSat

An attenuation-based method to retrieve vertical profiles of rainfall rates from height derivatives/gradients of CloudSat nadir-pointing W-band reflectivity measurements is discussed. This method takes advantage of the high attenuation of W-band frequency signals in rain and the low variability of nonattenuated reflectivity due to strong non-Rayleigh scattering from rain drops. The retrieval uncertainties could reach 40%–50%. The suggested method is generally applicable to rainfall rates (R) in an approximate range from about 2–3 to about 20–25 mm h⁻¹. Multiple scattering noticeably affects the gradients of CloudSat measurements for R values greater than about 5 mm h⁻¹. To avoid a retrieval bias caused by multiple-scattering effects, a special correction for retrievals is introduced. For rainfall rates greater than about 25 mm h⁻¹, the influence of multiple scattering gets overwhelming, and the retrievals become problematic, especially for rainfalls with higher freezing-level altitudes. The attenuation-based retrieval method was applied to experimental data from CloudSat covering the range of rainfall rates. CloudSat retrievals were compared to the rainfall estimates available from a National Weather Service ground-based scanning precipitation radar operating at S band. Comparisons between spaceborne and conventional radar rainfall retrievals were generally in good agreement and indicated the mutual consistency of both quantitative precipitation estimate types. The suggested CloudSat rainfall retrieval method is immune to the absolute calibration of the radar and to attenuation caused by the melting layer and snow regions. Since it does not require surface returns, it is applicable to measurements above both land and water surfaces.- Reference

Quality Assessment of Weather Radar Wind Profiles during Bird Migration

Wind profiles from an operational C-band Doppler radar have been combined with data from a bird tracking radar to assess the wind profile quality during bird migration. The weather radar wind profiles (WRWPs) are retrieved using the well-known volume velocity processing (VVP) technique. The X-band bird radar performed range–height scans perpendicular to the main migration direction and bird densities were deduced by counting and normalizing the observed echoes. It is found that the radial velocity standard deviation (σ_r) obtained from the VVP retrieval is a skillful indicator of bird migration. Using a threshold of 2 m s⁻¹ on σ_r, more than 93% of the bird-contaminated wind vectors are rejected while over 70% of the true wind vectors are accepted correctly. For high bird migration densities the raw weather radar wind vectors have a positive speed bias of 8.6 ± 3.8 m s⁻¹, while the quality-controlled wind vectors have a negligible speed bias. From the performance statistics against a limited area numerical weather prediction model, it is concluded that all (significant) bird contamination is removed and that high-quality weather radar wind profiles can be obtained, even during the bird migration season.- Reference

High-Resolution Observations of Insects in the Atmospheric Boundary Layer

High spatial and temporal resolution S-band radar observations of insects in the atmospheric boundary layer (ABL) are described. The observations were acquired with a frequency-modulated continuous-wave (FMCW) radar during the 2002 International H₂0 Project (IHOP_2002) held in Oklahoma in the months of May and June 2002. During the observational period the boundary layer was convective with a few periods of rain. Rayleigh scattering from particulate scatterers (i.e., insects) dominates the return; however, Bragg scattering from refractive index turbulence is also significant, especially at the top of the afternoon boundary layer. There is a strong diurnal signal in the insect backscatter: minima in the morning and at dusk and maxima at night and midafternoon. Insect number densities and radar cross sections (RCSs) are calculated. The RCS values range from less than 10⁻¹² m² to greater than 10⁻⁷ m² and likewise have a strong diurnal signal. These are converted to equivalent reflectivity measurements that would be reported by typical meteorological radars. The majority of reflectivity measurements from particulate scatterers ranges from −30 to −5 dBZ; however, intense point scatterers (>10 dBZ) are occasionally present. The results show that although insects provide useful targets for characterization of the clear-air ABL, the requirements for continuous monitoring of the boundary layer are specific to time of day and range from −20 dBZ in the morning to −10 to −5 dBZ in the afternoon and nocturnal boundary layer (NBL).- Reference

UK Hails Latest Spy Plane as a Success

The UK Royal Air Force (RAF) has hailed the Airborne Stand-Off Radar (ASTOR) system on the Sentinel R1 aircraft as a success after returning from trials in Afghanistan.

The aircraft is capable of operating for over nine hours at a time, during which it recognises and detects moving, static and fixed targets on the ground.

UK Minister for Defence, Equipment and Support, Quentin Davies said that the hugely sophisticated system successfully demonstrated what it could do in Afghanistan.

"The ASTOR system is a key element of the modern network-enabled battlefield, through which our forces can learn about the movement of enemy forces and react to prevent those threats to our troops," he said.

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