Ground-based Radar System Research Articles

MIMO Radar and Ground-Based SAR Imaging Systems: Equivalent Approaches for Remote Sensing

Currently there is an increasing interest in multiple-input multiple-output (MIMO) radars, because MIMO technology is able to provide a level of performance similar to that of a conventional antenna array, while also providing hardware and cost-related benefits. In this paper, we describe an upgrade of an existing ground-based synthetic aperture radar system (which is used for landslide monitoring) to a low-cost MIMO system. We also describe the associated low-cost/high-performance remote sensing benefits that this new configuration provides and present the results gathered by the new system. We conclude by outlining two configurations of the MIMO system with particular emphasis on antenna positioning, which has a key role in the overall performance.

Application of Integrated Modeling and Analysis to Development of Complex Systems

Model-based systems engineering (MBSE) is an approach to improve traditional document-based systems engineering approach through the use of a system model. In the current practice of system developments, there exists a large gap between systems engineering activities and engineering analyses, because systems engineers and engineering analysts are using different models, tools and terminology. The gap results in inefficiencies and quality issues that can be very expensive to fix. An integrated modeling and analysis capability was developed that bridges the gap. The technical approach is based on integrating SysML modeling tools with a process integration and design optimization framework. A capability was developed to automatically generate analysis models from a system model and then execute the analytical models. The integrated toolset enables engineers to quickly evaluate system configurations using realistic analysis models and automatically check requirements compliance. The capability was applied to a number of system development projects in industry, including a ground-based radar system. The integrated approach allowed the design teams to perform continuous design, analysis, and trade studies throughout the design process, and respond quickly to changes in requirements and design configurations.

Persistent wide area surveillance from an airship

Herein we have outlined a framework for investigation into the feasibility of using an airship equipped with a GMTI radar payload to provide persistent wide area surveillance sufficient to monitor vehicle and personnel movement on the ground. A study and analysis needs to be performed in order to determine the system requirements and the feasibility of modifying a currently existing radar system to adequately perform the required functions. This has described a methodology for determining if and how, existing airborne or ground-based MTI radar systems could be modified to perform these functions.

GB-SAR 간섭기법으로 측정된 X-밴드 대기 굴절률의 상대습도, 기온 및 기압에 따른 변화

이 논문은 X-밴드 Ground-Based Synthetic Aperture Radar (GB-SAR) 시스템을 이용하여 5개의 삼각삼면반사체(triangular trihedral corner reflector)의 시간에 따른 위상변화를 분석하였다. 각각의 반사체는 시스템으로부터의 거리를 다르게 설정하여 고정시켰고 모든 편파에 대한 영상을 20 분 간격으로 123 회, 총 40 시간 동안 연속 측정하였다. SAR 간섭기법(interferometry)을 이용한 분석 결과 반사체는 고정된 상태임에도 불구하고 시간에 따라 최대 2 radian의 위상차가 나타났으며 기상요소와 유사한 추세를 보였다. 대기 중 굴절률을 고려한 GB-SAR 위상관계식을 통하여 대기 중 습도, 기온 및 기압의 변화에 따른 마이크로파 굴절률의 변화 양상을 회귀분석을 통하여 살펴보았다. 그 결과 X-밴드의 굴절률은 습도 및 기온과 비교적 높은 선형적 관계를 보였으나(평균 결정계수 각각 0.72, 0.76) 기압과는 그렇지 않았다(결정계수 0.34). 실험 기간 동안 습도는 약 50 %에서 90 %까지, 기온은 <TEX>$-1^{\circ}C$</TEX>에서 <TEX>$9^{\circ}C$</TEX>까지 변하였으며 X-밴드 굴절률의 변화는 약 <TEX>$3.14{\times}10^{-5}$</TEX>였다. 향후 보다 다양한 기상조건에서 실험이 이루어진다면 습도, 기온 및 기압 조건에 따른 굴절률의 포괄적 관계식을 유추할 수 있을 것으로 기대된다. In this paper, we analyzed the phase change of 5-triangular trihedral comer reflectors by using X-band Ground-Based Synthetic Aperture Radar (GB-SAR) system. Each reflector was set as a stationary target at a different distance from the system. We obtained total 123 full-polarization images during 40 hours continuously at 20 minute interval. Results of SAR interferometric analysis showed phase changes of maximum 2 radians and followed similar pattern with atmospheric data. Through a GB-SAR phase formula that includes refractive index in the air, we performed regression analysis for refractive index as a function of atmospheric humidity, temperature and pressure. As a result, refractive index of air in X-band showed relatively high coefficient of determination with humidity and temperature (0.72 and 0.76 on average, respectively) but not so with pressure (0.34). The refractive index of air in X -band changed by <TEX>3.14\;{\times}\;10^{-5}$</TEX> during the measuring time with a humidity range of 50% ~ 90% and a temperature range of <TEX>$-1^{\circ}C$</TEX> ~ <TEX>$9^{\circ}C$</TEX>. We expect that a total expression of refractive index of air including humidity, temperature and pressure can be calculated when more extensive data would be collected at various atmospheric conditions.

Ice radar investigation at Dome A, East Antarctica: Ice thickness and subglacial topography

Dome A, located in the central East Antarctic ice sheet (EAIS), is the highest summit of the Antarctic ice sheet. From ice-sheet evolution modeling results, Dome A is likely to preserve over one million years of the Earth’s paleo-climatic and -environmental records, and considered an ideal deep ice core drilling site. Ice thickness and subglacial topography are critical factors for ice-sheet models to determine the timescale and location of a deep ice core. During the 21st and 24th Chinese National Antarctic Research Expedition (CHINARE 21, 2004/05; CHINARE 24, 2007/08), ground-based ice radar systems were used to a three-dimensional investigation in the central 30 km×30 km region at Dome A. The successfully obtained high resolution and accuracy data of ice thickness and subglacial topography were then interpolated into the ice thickness distribution and subglacial topography digital elevation model (DEM) with a regular grid resolution of 140.5 m×140.5 m. The results of the ice radar investigation indicate that the average ice thickness in the Dome A central 30 km×30 km region is 2233 m, with a minimal ice thickness of 1618 m and a maximal ice thickness of 3139 m at Kunlun Station. The subglacial topography is relatively sharp, with an elevation range of 949–2445 m. The typical, clear mountain glaciation morphology is likely to reflect the early evolution of the Antarctic ice sheet. Based on the ice thickness distribution and subglacial topography characteristics, the location of Kunlun Station was suggested to carry out the first high-resolution, long time-scale deep ice core drilling. However, the internal structure and basal environments at Kunlun Station still need further research to determine.

Comparison and Evaluation of Ship Detection and Identification Algorithms Using Small Boats and ALOS-PALSAR

The final goal of the present project is to develop a ship detection and identification system by integrating spacebome synthetic aperture radar (SAR), ground-based maritime radar and automatic identification system (AIS); and this article presents the results of the first phase experiments and current status toward achieving this goal. The data acquired by the Phased Array L-band SAR (PALSAR) on board of the Advanced Land Observing Satellite (ALOS) were used as SAR data, and X-band maritime radar including AIS were used as a ground-based system. The work is divided into two experimental phases. The first phase is to examine the ability of PALSAR to detect ships whose sizes are comparable with the SAR resolution cells, and the second is to incorporate the PALSAR data with those acquired by the ground-based radar with AIS. For the experiments in the first phase, we deployed three small fishing boats whose lengths ranged from approximately 8 m to 15 m in the Tosa Bay in Kochi, Japan in 2006. The experiments were carried out for four observation PALSAR modes: FBS (Fine Beam Single) 34.3, FBS 21.5, FBD (Fine Beam Double) 41.5, and PLR (PoLaRimetric) 20.5, where the numbers in each modes represent the off-nadir angles. For extracting the boats from the PALSAR images, five algorithms were considered, including amplitude-based, CFAR (Constant False Alarm Rate), MLCC (Multi-Look Cross-Correlation), CCF (Cross-Correlation Function) of HH- and HV-polarization amplitudes, and polarimetric analyses. This paper summarizes the results of the first phase experiments; the summary of the integrated system in the second phase will be reported in the near future.

A low-frequency ice-penetrating radar system adapted for use from an airplane: test results from Bering and Malaspina Glaciers, Alaska, USA

AbstractIce-thickness measurements are needed to calculate fluxes through fast-flowing outlet glaciers in Greenland, Alaska, Patagonia and Antarctica. However, relatively high attenuation of radio waves by dielectric absorption and volume scattering from englacial water hampers detection of the bed through warm deep ice. In the past we have had success measuring ice thickness of temperate glaciers using a ground-based monopulse radar system operating at low frequencies (2 MHz). Here we adapt the same system to operate from an airplane. Test flights over Bering Glacier, Alaska, USA, detected the bed through ice up to 1250m thick. Flights across the Seward–Malaspina Glacier system, Alaska, resolved the ice thickness of Malaspina Glacier, but strong hyperbolic-shaped returns obscured the bed echo through the Seward throat. It is likely that this clutter in the signal was caused by off-nadir returns from chaotic surface crevasses that are ubiquitous in the throat region.

Classification of Ground Clutter and Anomalous Propagation Using Dual-Polarization Weather Radar

This paper presents the results of a study designed to classify weather radar clutter echoes obtained from ground-based dual-polarization weather radar systems. The clutter signals are due to ground clutter, sea clutter, and anomalous propagation echoes, which represent sources of error in quantitative radar rainfall estimation. Fuzzy and Bayes classifiers are evaluated as an alternative approach to traditional polarimetric-based methods. Both systems were trained and validated by using C-band dual- polarization radar measurements, and a novel technique is proposed to calculate the texture function to mitigate against the edge effects at the boundaries of precipitation regions. A methodology is presented to extract the membership functions and conditional probability density functions to train the classifiers. The critical success index indicates that the Bayes classifier has, on average, a slightly better performance than the fuzzy classifiers. However, when optimal weighting was applied, the fuzzy classifier gave one of the best performances. The classifiers are sufficiently robust to be used when only single-polarization radar measurements are available.

Volcanic Ash Cloud Retrieval by Ground-Based Microwave Weather Radar

The potential of ground-based microwave weather radar systems for volcanic ash cloud detection and quantitative retrieval is evaluated. The relationship between radar reflectivity factor, ash concentration, and fall rate is statistically derived for various eruption regimes and ash sizes by applying a radar-reflectivity microphysical model. To quantitatively evaluate the ash detectability by weather radars, a sensitivity analysis is carried out by simulating synthetic ash clouds and varying ash concentration and size as a function of the range. Radar specifications are taken from typical radar systems at S-, C-, and X-band. A prototype algorithm for volcanic ash radar retrieval (VARR) is discussed. Starting from measured single-polarization reflectivity, the statistical inversion technique to retrieve ash concentration and fall rate is based on two cascade steps, namely: 1) classification of eruption regime and volcanic ash category and 2) estimation of ash concentration and fall rate. Expected accuracy of the VARR algorithm estimates is evaluated using a synthetic data set. An application of the VARR technique is finally shown, taking into consideration the eruption of the Grinodotacutemsvoumltn volcano in Iceland on November 2004. Volume scan data from a Doppler C-band radar, which is located at 260 km from the volcano vent, are processed by means of the VARR algorithm. Examples of the achievable VARR products are presented and discussed

Microphysical characterization of microwave Radar reflectivity due to volcanic ash clouds

Ground-based microwave radar systems can have a valuable role in volcanic ash cloud monitoring as evidenced by available radar imagery. Their use for ash cloud detection and quantitative retrieval has been so far not fully investigated. In order to do this, a forward electromagnetic model is set up and examined taking into account various operating frequencies such as S-, C-, X-, and Ka-bands. A dielectric and microphysical characterization of volcanic vesicular ash is carried out. Particle size-distribution (PSD) functions are derived both from the sequential fragmentation-transport (SFT) theory of pyroclastic deposits, leading to a scaled-Weibull PSD, and from more conventional scaled-Gamma PSD functions. Best fitting of these theoretical PSDs to available measured ash data at ground is performed in order to determine the value of the free PSD parameters. The radar backscattering from spherical-equivalent ash particles is simulated up to Ka-band and the accuracy of the Rayleigh scattering approximation is assessed by using an accurate ensemble particle scattering model. A classification scheme of ash average concentration and particle size is proposed and a sensitivity study of ash radar backscattering to model parameters is accomplished. A comparison with C-band radar signatures is finally illustrated and discussed.

Generation of digital terrain models with a ground-based SAR system

A novel technique for the retrieval of a digital terrain model (DTM) with a ground-based synthetic aperture radar (GB-SAR) system is described. A set of SAR images collected over a test site located at Salice d'Ulzio, Italy, is used to validate experimentally the proposed DTM retrieval technique. The topographic height is obtained using an algorithm specifically tailored for a GB-SAR system equipped with two receive antennas. The comparison with an existing DTM of the test site area shows that the retrieved DTM is accurate, with root mean square height differences between the two DTMs below 5 m.

Development of a ground-based polarimetric broadband SAR system for noninvasive ground-truth validation in vegetation monitoring

We have developed a ground-based polarimetric broadband synthetic aperture radar (SAR) system for noninvasive ground-truth validation in polarimetric SAR remote sensing of terrestrial vegetation cover. This system consists of a vector network analyzer, one dual-polarized antenna, and an antenna positioner. It can be operated in a frequency range from 50 MHz to 20 GHz, with a scanning aperture of 20 m in the horizontal and 1.5 m in the vertical direction. Tests carried out with standard reflectors showed that the polarimetric measurement capabilities of this system are satisfactory. Using the polarimetric ground-based SAR (GB-SAR) system, we carried out measurements on a specific vegetation cover pertinent to the remote sensing of forested regions within Sendai City, consisting of three different kinds of trees common within the Kawauchi Campus of Tohoku University. Measurements were collected in spring, summer, and autumn. Three-dimensional (3-D) polarization-sensitive images were reconstructed from the acquired data. Analysis of the 3-D polarimetric images of each measurement found differences (at times strong differences) among the polarization signatures. There were stronger reflections in all of the HH, VH, VV images in the second (summer) measurement, especially in the VH image, due to the substantial growth of branches and leaves in summer. This ground-truth validation system provided valuable information about the scattering mechanisms of the three trees selected for analysis in different seasons, which can be detected by broadband polarimetric ground-based SAR measurements. The experimental results demonstrate the excellent polarimetric performance of the newly developed SAR imaging system, which should find many useful and immediate applications in noninvasive ground-truth validation of diverse terrestrial vegetation covers.

On the Flux of Extrasolar Dust in Earth’s Atmosphere

Micron-size extrasolar dust particles have been convincingly detected by satellites. Larger extrasolar meteoroids (5-35 μm) have most likely been detected by ground-based radar at Arecibo and New Zealand. We present estimates of the minimum detectable particle sizes and the collecting areas for both radar systems. We show that particles larger than ~10 μm can propagate for tens of parsecs through the interstellar medium, opening up the possibility that ground-based radar systems can detect AGB stars, young stellar objects such as T Tauri stars, and debris disks around Vega-like stars. We provide analytical and numerical estimates of the ejection velocity in the case of a debris disk interacting with a Jupiter-mass planet. We give rough estimates of the flux of large micrometeoroids from all three classes of sources. Current radar systems are unlikely to detect significant numbers of meteors from debris disks such as β Pictoris. However, we suggest improvements to radar systems that should allow for the detection of multiple examples of all three classes.

Vector subspace detection in compound-Gaussian clutter. Part II: performance analysis

For pt. I see ibid., vol. 38, no. 4, p. 1295 (2002). In this second part we deal with the problem of detecting subspace random signals against correlated non-Gaussian clutter modeled by the compound-Gaussian distribution. In the first part of the paper, we derived the optimum Neyman-Pearson (NP) detector, the generalized likelihood ratio test (GLRT), and a constant false-alarm rate (CFAR) detector; we also provided some interesting interpretations of them. In this second part, these detectors are tested against both simulated data and measured high resolution sea clutter data to investigate the dependence of their performance on the various clutter and signal parameters. Numerical examples concern a space-time adaptive processing (STAP) scenario and a ground-based surveillance radar system scenario.

Scattering of VHF radio waves from within the top 700 m of the Antarctic ice sheet and its relation to the depositional environment: a case-study along the Syowa–Mizuho–Dome Fuji traverse

AbstractRadio-wave scattering is a convenient method to image the properties of large internal regions of ice sheets. We used a ground-based radar system with short pulses of 60 and 179MHz frequencies to scatter off internal strata within 100–700 m of the surface in the ice sheet of East Antarctica. Data were examined along an 1150 kmlong traverse line that was approximately along the ice flowline from inland of Dome Fuji station to the coast. The scattered waves are from strata, and the dominant cause of the scattering was changes in dielectric permittivity across the strata. Therefore, density fluctuations primarily cause the scattering, although variations in ice-crystal fabrics and acidity could also have effects. The power scattered from the same depths varied by &gt; 15 dB from one location to another. These variations correlate with the accumulation rate, changes in the surface slope, and subglacial bedrock undulations. Variations of the scattered power suggest that density contrasts in the strata are highly variable depending on these interdependent local conditions. The distribution of strata along the route allowed estimates of the ice-flow trajectories to depths of about 250 m.

On the application of MUSCAT to a ground-baseddual-Doppler radar system

The multiple-Doppler synthesis and continuity adjustment technique (MUSCAT), developed for at least a pair of Doppler observations, is based on both a simultaneous resolution of the equations relating the wind components to the measured radial velocities and of the continuity equation, and the use of second-order derivatives in the cost function. It has been developed to solve the geometrical limitations that result from a dual-Doppler radar configuration, and has been successfully applied to airborne radar equipped for a fore-aft scanning. This paper intends to show the performance of this method in the case of a differing geometry from a ground-based dual-Doppler radar system, using simulated Doppler data deduced from an analytical wind field. It is shown that the constraint on the second-order derivatives allows to also obtain reliable wind vectors outside the Doppler lobes, i.e., in regions along the radar baseline where ill-conditioned analysis occurs.

Coincident In Situ and W-Band Radar Measurements of Drop Size Distribution in a Marine Stratus Cloud and Drizzle

Abstract Investigation of precipitation formation requires measurements of the drop size distribution in a cloud. These measurements have usually been made using ground-based radar systems or aircraft in situ probes. Difficulties encountered in practice using these systems include accounting for the air motion at points remote from the radar systems and small sample volumes measured using the aircraft probes. An airborne W-band radar system provides a measurement from a much larger sample volume, close to the aircraft, with a correction for air motion possible using the data from the aircraft inertial navigation system. The Coastal Stratus Experiment conducted off the coast of Oregon in late 1995 provided W-band radar and microphysical probe data sampled from much of the same region of a marine stratus cloud. The unique combination of cloud probes and W-band radar on board the University of Wyoming King Air allowed the radar sampling to be only 60 m away from the probe sampling region. Doppler spectrum da...

Attenuation in Rain for X- and C-Band Weather Radar Systems: Sensitivity with respect to the Drop Size Distribution

Abstract This paper is devoted to a sensitivity study of the equation describing attenuation effects in rain for ground-based weather radar systems operating at X- or C-band wavelengths. First, the so-called attenuation equation, also termed the HB solution or HB algorithm in reference to the well-known paper by Hitschfeld and Bordan, is recalled. A procedure aimed at obtaining consistent relations between average values of the equivalent reflectivity factor Ze, the attenuation coefficient k, and the rain rate R as function of two parameters of the drop size distribution (DSD) is also presented. Then, a numerical simulation framework based on a simple description of rainfall characteristics and accounting for some of the radar measurement features is proposed to test the ability of the HB algorithm to perform attenuation correction of hypothetical rain-rate profiles. In a first step, the well-known instability of the solution is illustrated. For instance, it is shown that, even in the absence of radar cal...

Feasibility of employing artificial neural networks for emergent crop monitoring in SAR systems

An investigation into the feasibility of using high-resolution synthetic aperture radar (SAR) data and artificial neural networks for monitoring the stage of growth of a crop is presented. The high resolution data sets representing an experimentally simulated crop at three different stages of growth are acquired at X-band by means of a ground-based synthetic aperture radar (GB-SAR) system under development at the University of Sheffield. A hybrid classification system, developed in recent studies, is then applied to these image sets, providing very high training and test data accuracy (95.8% and 94.4%, respectively) for differences in growth of the order of a quarter of a wavelength, and acceptable results (79.9% and 71.9%, respectively) for differences of the order of a tenth of a wavelength. The procedures developed for the high-resolution data acquisition are described and the results obtained by applying the hybrid classification system to the acquired data are discussed.

Doppler Radar Analysis of the Northfield, Texas, Tornado of 25 May 1994

Abstract A large tornado was observed near Northfield, Texas, on 25 May 1994 during the Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX). An analysis of the tornado and its parent storm is discussed. Doppler wind velocity spectra of the tornado and its parent circulation, which were computed from data collected by a low-power, portable, FM-CW (frequency-modulated continuous-wave), 3-cm-wavelength Doppler radar, are presented at increments in the range of 78 m. The FM-CW radar data from the tornado are the first ever collected of high enough quality to analyze. The CW spectra computed from data collected by the portable radar, a pseudo-dual-Doppler analysis of airborne Doppler radar data collected by a National Oceanic and Atmospheric Administration P-3 aircraft, photogrammetric analysis of a video of the tornado, and a ground-based damage survey are discussed in the context of the FM-CW spectra. This study is unique in that both ground-based and airborne Doppler radar systems probe...