Radar System Parameters Research Articles

Signal degradation through sediments on safety-critical radar sensors

Abstract. This paper focusses on a transmission line (TL) based model which allows to investigate the impact of multilayered obstructions in the propagating path of a radar signal at different distances and in combination with disturbances. Those disturbances can be water, snow, ice, and foliage at different densities, temperatures, positions, with a given thickness and layer combination. For the evaluation of the detectability of objects, the impulse response of the system can be obtained. Investigations employing state-of-the-art radar hardware confirm the consistency of theoretical and experimental results for 24 and 77 GHz. The analysis in this paper supports testing the specifications for radar systems, before carrier frequency and antenna layout are finally decided. Thereby, the radar system parameters can be adjusted toward employed carrier frequency, bandwidth, required sensitivity, antenna and amplifier gain. Since automotive standards define operational environmental conditions such as temperature, rain rate, and layer thickness, these parameters can be included and adapted. A novel optimisation methodology for radomes is presented which allows to boost the dynamic range by almost 6 dB with presence of a worst-case cover layer of water. The findings can be utilised to properly design radar systems for automotive applications in autonomous driving, in which other vulnerable road users have to be protected under all circumstances.

Analysis of ship wake features and extraction of ship motion parameters from SAR images in the Yellow Sea

The identifying features of ship wakes in synthetic aperture radar (SAR) remote sensing images are of great importance for detecting ships and for extracting ship motion parameters. A statistical analysis was conducted on the identifying features of ship wakes in SAR images in the Yellow Sea. In this study, 1091 ship wake sub-images were selected from 327 SAR images in the Yellow Sea near Qingdao. Analysis of the identifying features of ship wakes in SAR images revealed that both turbulent wakes and Kelvin wakes account for the majority of ship wakes, with turbulent wakes occurring approximately four times as frequently as Kelvin wakes. Narrow- V wakes and internal wave wakes were comparatively rare, which is due to the peculiarities of the radar system parameters and marine environments required to observe these wakes. Additionally, we extracted ship motion parameters from four types of ship wakes in the SAR images. Specifically, internal wave wakes in SAR images in the Yellow Sea were also used to extract ship motion parameters. Validation of the extracted parameters indicated that the extraction of these parameters from ship wakes is a viable and accurate approach for the acquisition of ship motion parameters. These results provide a solid foundation for the commercialization of SAR-based technologies for detecting ships and extracting ship motion parameters.

Soil Moisture Retrival Based on Sentinel-1 Imagery under Sparse Vegetation Coverage.

Soil moisture is an important aspect of heat transfer process and energy exchange between land-atmosphere systems, and it is a key link to the surface and groundwater circulation and land carbon cycles. In this study, according to the characteristics of the study area, an advanced integral equation model was used for numerical simulation analysis to establish a database of surface microwave scattering characteristics under sparse vegetation cover. Thus, a soil moisture retrieval model suitable for arid area was constructed. The results were as follows: (1) The response of the backscattering coefficient to soil moisture and associated surface roughness is significantly and logarithmically correlated under different incidence angles and polarization modes, and, a database of microwave scattering characteristics of arid soil surface under sparse vegetation cover was established. (2) According to the Sentinel-1 radar system parameters, a model for retrieving spatial distribution information of soil moisture was constructed; the soil moisture content information was extracted, and the results were consistent with the spatial distribution characteristics of soil moisture in the same period in the research area. (3) For the 0–10 cm surface soil moisture, the correlation coefficient between the simulated value and the measured value reached 0.8488, which means that the developed retrieval model has applicability to derive surface soil moisture in the oasis region of arid regions. This study can provide method for real-time and large-scale detection of soil moisture content in arid areas.

Analysis of Security Imaging Method for Walking Human Screening With Single Channel Synthetic Aperture Radar

In this paper, a security screening imaging method for walking human with single channel synthetic aperture radar (SAR) technology is proposed. According to the theory of SAR imaging, the imaging response for each single echo of the three dimensional (3D) moving target is analyzed. Then, the relationships between the accurate degree of imaging result and radar system parameters are presented with the global human walking model, which can be summarized as: positive correlations with radar angular velocity and rotation radius, negative correlations with aperture time and motion velocity, and uncertainty with radar initial angle. Hence, the short synthetic aperture time and high-resolution of terahertz (THz) radar makes it particularly suitable for walking human security imaging. Meanwhile, the main Doppler frequency shift of walking human imaging is corrected by the back-projection (BP) algorithm modified with the estimated velocity detected by the range profile. Besides, the numerical simulation experiments of point targets are provided to verify the conclusion of moving target imaging response. Furthermore, the experiments of walking human are processed with different radar system parameters to demonstrate the performance and effectiveness of our method.

Off‐grid effects mitigation exploiting knowledge of the clutter ridge for sparse recovery STAP

In this study, a novel method for overcomplete dictionary construction for sparse recovery (SR) space–time adaptive processing (STAP) is proposed, which can effectively mitigate the off-grid effect. The proposed method utilises the clutter ridge, calculated via some prior knowledge such as radar system parameters and modern inertial navigation system information, to discretise the grids in the angle–Doppler plane. The authors also investigate the accuracy of clutter ridge in the presence of several typical non-ideal factors such as array errors, intrinsic clutter motion and aircraft crab. In particular, a parameter is introduced to adaptively adjust the grid interval to avoid the strong column coherence of the dictionary. The simulation results show that the signal-to-clutter-plus-noise ratio for the SR STAP with the proposed dictionary is significantly improved, compared with the one utilising conventional dictionary. Moreover, it is shown that the novel method not only works more robustly for the side-looking array, but also has better performance for other array orientations.

Geomorphometric analysis of the 2014–2015 Bárðarbunga volcanic eruption, Iceland

Topographical information is of fundamental interest for a wide range of disciplines including glaciology, agriculture, communication network planning, or hazard management. In volcanology, elevation data are of particular importance when assessing material flows throughout a volcanic system. To obtain accurate estimates of time-varying topography in volcanic active regions, high-resolution digital elevation models (DEMs) are required. To monitor and evaluate topographical changes and especially volumetric gains and losses during the 2014–2015 Bárðarbunga eruption, Iceland, multi-temporal TanDEM-X DEM sequences were evaluated.The 2014–2015 volcanic eruption was associated with the rare event of a caldera collapse, visible on the surface of the Vatnajökull glacier, as well as major lava effusion in the Holuhraun plain. Before investigating topographical change at the two study areas, the TanDEM-X DEMs were analysed for absolute and relative height errors resulting from the radar system parameters, the SAR processing or the local environment. The uncertainty investigation determined that acquisitions over the snow-covered Bárðarbunga caldera were primarily affected by microwave penetration into snow and DEMs over the Holuhraun lava field exhibited increased height errors due to active lava flows and dynamic outwash plain.The topographical analysis of the 2014–2015 Bárðarbunga eruption revealed a maximum vertical displacement of approximately −65m and +43m at the study area of the Bárðarbunga caldera and Holuhraun lava field respectively. With a total subsidence volume of −1.40±0.13km3 and a dense-rock equivalent (DRE) lava volume of +1.36±0.07km3, known uncertainties in volume were decreased by approximately 35% and 77% accordingly. Taking into account the calculation of rates, the temporal development of caldera collapse and lava effusion was found to exhibit a near-exponential decrease. The ratio between subsidence and DRE lava volume moreover indicated the coupling between piston collapse and magma drainage.

Study on the Simulation System of MPL

In this paper, according to the working principle of lidar and standard atmosphere model ,a micro-pulse lidar simulation model is designed. By simulated atmospheric echo signal strength, we can demonstrate the effectiveness of radar system parameters, and determine the optimal value of each parameter.

Time-frequency tomographic imaging of a rotating object in a narrow-band radar

The backscatter from radar object carries Doppler information of scatterers on the object determined by the radial velocity of scattering points and the radar transmitted frequency. For a rotating object this information is contained in the frequency characteristics over varying aspect angle. Frequency characteristics are used to create projections for Doppler radar tomographic imaging. This paper presents a method for high resolution imaging of a rotating target using a time-frequency transform of a returned signal as tomographic projections. The resolution of a tomographic image depends not only on radar system parameters but also depends on the resolution of input projections. The reassigned spectrogram is proposed for building of tomographic projections, due to its possibility of squeezing of frequency spread. The reassigned spectrogram is sensitive to noise so the denoising procedure in the time-frequency domain must be performed before the reassignment procedure. The denoising is performed by removing Short Time Fourier Transform (STFT) noise coefficients below the appropriate threshold. The STFT is a linear time-frequency transform and coefficients, which belong to the signal and coefficients which belong to noise can be analyzed separately. The efficiency of the proposed idea of imaging is supported by results of numerical experiments.

Influence of significant radar system parameters on resolution of image in Doppler Radar Tomography

Doppler radar tomography is a method of creation of a target image from Doppler profiles of a rotating target. Electromagnetic backscattering from rotating objects generates time-varying Doppler spectra which can be a base of tomographic projections in the time-frequency approach. In this paper the influence of projections and significant radar system parameters on the final image resolution is considered. The results of simulations of the proposed imaging method are also presented. Streszczenie. Dopplerowska tomografia radarowa jest metodą formowania obrazow obracających sie obiektow radarowych z profili Dopplerowskich. Rozpraszanie fali elektromagnetycznej przez rotujacy obiekt powoduje powstanie czasowo zmiennych charakterystyk czestotliwościowych, ktore są bazą rzutow tomograficznych w podejściu czas-czestotliwośc. Rozwazono wplyw jakości rzutow tomograficznych oraz istotnych dla zobrazowania parametrow systemu radarowego na rozdzielczośc tworzonego obrazu. Przedstawiono rowniez rezultaty symulacji. Wplyw parametrow radaru na rozdzielczośc obrazu Dopplerowskiej Tomografii Radarowej

Robust space-time adaptive processing for nonhomogeneous clutter in the presence of model errors

In this paper, we first develop a novel array self-calibration method for estimating array gain-phase errors by computing the clutter subspace from the radar system parameters and using the clutter data in space-time adaptive processing (STAP). The proposed algorithm is shown to perform well even in nonhomogeneous clutter, and it can improve the performance of existing STAP algorithms, such as the clutter subspace-based method in the presence of array gain-phase errors.We also develop a two-stage STAP approach for suppressing nonhomogeneous clutter in the presence of model errors in addition to array gain-phase errors. In our two-stage STAP approach, the first stage explores the clutter subspace calculated from the radar system parameters to suppress the main clutter. The second stage employs the conventional method, such as the partially adaptive sample matrix inversion STAP method, to remove any residual clutter. Numerical results illustrate the benefits of the array self-calibration method and the effectiveness of the two-stage STAP method. Finally, the performance of the three STAP methods is compared via the well-known MCARM data set. The results further confirm that there is an improvement in performance when using array self-calibration together with the two-stage STAP method.

Limiting accuracy of the dual-frequency microwave interferometry measurement for sea surface monitoring from space

The method based on the dual-frequency correlation function of reflected signals is one of the effective approaches for sea wave height estimation in radar altimetry. This method, however, has been applied for relatively low-altitude flights. As shown in our early studies, for the estimation of the sea wave heights using the dual-frequency correlation function, it is necessary to synthesize the array antennas, which are perpendicular to the flight direction. In this paper, we derived the limiting accuracy of the measurement of the sea wave heights using the dual-frequency microwave interferometry, and analyzed its dependence on the sea wave heights and the radar system parameters. Evaluation of the limiting accuracy of the measurement of the sea wave heights shown in the paper verified its high accuracy for sea status monitoring using a small remote sensing spacecraft.

Multiaircraft formation identification for narrowband coherent radar in a long coherent integration time

In this paper, we first propose a novel multiaircraft formation (MAF) signal model for narrowband coherent radar in a long coherent integration time (LCIT). We then give a quantitative analysis on the phase order approximation of the MAF echoes according to the LCIT duration with a given set of target motion and radar system parameters. It is shown that these echoes in a certain LCIT can be well approximated by multiple chirp signals or multiple cubic phase signals for MAFs with rigid or nonrigid structures,respectively. Subsequently, we propose to apply third-order polynomial Fourier transform (PFT), to accurately estimate the MAF parameters, which include aircraft number and different order motion parameters for each aircraft. The performance of third-order PFT is compared with the existing third-order polynomial generalized Radon transform (GRT) in time-frequency domain. It is shown that the third-order PFT has higher parameter estimation resolution than the third-order polynomial GRT, as well as higher estimation accuracies with some additional computational complexity. Finally, some numerical experiments are provided to demonstrate the effectiveness of the proposed MAF model and the parameter estimation method by using simulation and real measured data.

Assessment of radar‐derived snow depth over Arctic sea ice

AbstractKnowledge of contemporaneous snow depth on Arctic sea ice is important both to constrain the regional climatology and to improve the accuracy of satellite altimeter estimates of sea ice thickness. We assess new data available from the NASA Operation IceBridge snow radar instrument and derive snow depth estimates across the western Arctic ice pack using a novel methodology based on wavelet techniques that define the primary reflecting surfaces within the snow pack. We assign uncertainty to the snow depth estimates based upon both the radar system parameters and sea ice topographic variability. The accuracy of the airborne snow depth estimates are examined via comparison with coincident measurements gathered in situ across a range of ice types in the Beaufort Sea. We discuss the effect of surface morphology on the derivation, and consequently the accuracy, of airborne snow depth estimates. We find that snow depths derived from the airborne snow radar using the wavelet‐based technique are accurate to 1 cm over level ice. Over rougher surfaces including multiyear and ridged ice, the radar system is impacted by ice surface morphology. Across basin scales, we find the snow‐radar‐derived snow depth on first‐year ice is at least ∼60% of the value reported in the snow climatology for the Beaufort Sea, Canada Basin, and parts of the central Arctic, since these regions were previously dominated by multiyear ice during the measurement period of the climatology. Snow on multiyear ice is more consistent with the climatology.

Transmit Subaperturing for Range and Angle Estimation in Frequency Diverse Array Radar

Different from conventional phased-array, which provides only angle-dependent beampattern, frequency diverse array (FDA) employs a small frequency increment across the antenna elements and results in a range-angle-dependent beampattern. This beampattern offers a potential to localize the targets in two dimensions in terms of slant ranges and azimuth angles. However, it is difficult to obtain the target location information from a standard FDA radar due to the couplings in range and angle responses. In this paper, we propose a transmit subaperturing scheme on the FDA radar for range and angle estimation of targets. The essence is to divide the FDA elements into multiple subarrays and optimize the transmit beamspace matrix with the use of convex optimization. We also discuss several practical issues for designing the FDA radar system parameters. Since the subarrays offer decoupled range and angle responses, the targets can be located using the beamspace-based multiple signal classification algorithm. The range and angle estimation performance is evaluated by comparing with the Cramer-Rao lower bound.

ASSESMENT AND EVLUATION OF THE IMPACT OF USING POLSAR IMAGERIES WITH DIFERENT INCIDENT ANGLES IN FOREST CLASSIFICATION

Abstract. Forests are a dominant biome of the earth and have an important impact on its economic and environmental well-being. Forestry applications of radar remote sensing are addressed in the context of both forest management and ecosystem understanding, modelling and monitoring. Nowadays, radar remote sensing is being used for a lot of applications in various fields. Due to the applications of polarimetric radar in recent decades, many researchers have tended to this field. One of the main advantages of SAR images is that these images are independent over the time (day and night) and weather condition. The polarimetric SAR (POLSAR) images compared with other remote sensing images are more informative. Classification of radar images is a way by which we can separate different types of forest species. In addition to the main characteristics of the target, the backscatter from a SAR image is widely dependant on various radar system parameters. One of these system parameters is the incident angle of the radar system. In this paper, the impact of using PolSAR images with different incidence angles for the classification of forest areas is investigated. Two polSAR images with different incident angles taken by RADARSAT-2 in fine quad polarized mode (FQ4 and FQ18) have been used in this study. The study area is located in the Petawawa Research Forest (PRF) near Chalk River, Ontario, Canada The methodology of this paper contains three steps: (1) preprocessing, (2) wishart classification and (3) evaluating & analyzing the results. The preprocessing steps consist of the speckle noise filtering, covariance matrix extraction and georeferencing. In the second step, each incidence angle image was classified by using the supervised Wishart classification. The Wishart classification method has the capability of having multiple images at the same time. Thus, in the next experiment the classification was performed using both incidence angle images. Finally, the obtained results from each class and the classification results in each of three cases were evaluated and analyzed. The results showed that Wishart classification provides an overall accuracy of % 67.17 using the lower incidence angle PolSAR image and % 65.38 for the higher incidence angle POLSAR image. Also, the overall accuracy of the simultaneous classification by using the extracted covariance matrix from both images is 72.63 %. Those results showed a better performance of the image with lower incident angle compared to that of an image with higher incident angle for forest classification. It is also shown that combining extracted covariance matrix from the FQ4 image with extracted covariance matrix from the FQ18 image can significantly improve the classification accuracy (overall accuracy).

Simulation of the parameters of the meteor radar system in order to optimize its operation

Since 1966 the Meteor Automated Radar System (MARS) has been operating at the Balakleya scientific testing ground of the Kharkov National University of Radio Electronics, which had provided with the unique scientific data on meteors and the earth's atmosphere.For a long time of operation the equipment has undergone considerable moral and physical obsolescence. The need to continue the meteoric research on the one hand, and the inability to do so on the available equipment on the other hand, requires the modernization of the complex with regard of the new objectives and new opportunities.Simple switch to the new element base without taking into account the changing of the working conditions and new research objectives is not reasonable. It is necessary to revise a number of parameters of the available equipment. A large number of factors can be found by means of modeling of the improved complex. However, the simulation can not be carried out without a major component - the model of the meteor-trail reflections. Therefore, the primary problem is to develop a model that would include the ground-based research equipment parameters and the model of the processes occurring in the meteor zone as well.The article proposes the structure of this model, presents the analytical concepts for some modeling stages and their graphic interpretation. The above model is implemented as a computer program. The above model is implemented as a computer program. It differs by the change of the signal amplitude in the meteor trail formation process; the ability to model meteor propagation to the "ultra-short" routs - between the main and offset points; as well as to determine the trail coordinates, which is necessary for further determination of the meteor radiant.

MOVING-TARGET VELOCITY ESTIMATION IN A COMPLEX-VALUED SAR IMAGERY

In the ground moving target indication with synthetic aperture radar (SAR) community, algorithms used to estimate the velocity of a detected moving target are important because they are relative to the topics about refocusing and azimuth displacement correction. The velocity is regarded as a vector with two components, one in azimuth and one in range direction, and new algorithms aiming at estimating the two components are proposed and verifled. The range velocity estimator transforms a detected patch containing a moving target to range Doppler domain by using the 1-D fast Fourier Transform in each range bin to achieve its range Doppler locus. The slope of the range Doppler locus is computed by using the Radon Transform on the range Doppler plane and the range velocity component is worked out according to radar system parameters and the slope value. Two estimators are proposed to compute the azimuth velocity component. One is based on symmetric defocusing in Doppler domain, the other is based on phase gradient in wave-number domain. Experiments conflrm the efiectiveness of the estimators by using simulated and fleld data.

Multistatic and Multiple Frequency Imaging Resolution Analysis-Application to GPS-Based Multistatic Radar

This paper focuses on the computation of the generalized ambiguity function (GAF) of a multiple antennas multiple frequencies radar system (MAMF). This study provides some insights into the definition of resolution parameters of a MAMF radar system. It turns out that the range and azimuth resolutions are not the most suitable criteria to specify the MAMF radar resolution. Therefore a new set of resolution parameters is introduced like the resolution ellipse which expresses the resolution anywhere in the image plane or δ→max, (δ→min) which expresses the highest (lowest) bound of the spatial radar resolution. To point out the pertinence of our study, we illustrate it with a MAMF radar system built around GPS satellites. The effect of the radar system geometry on resolution is investigated. For several scenarios, the GAF and its numerical form, the point spread function (PSF), are computed and their results are compared.

Extended ambiguity function for bistatic MIMO radar

This paper derives the extended ambiguity function for a bistatic multiple-input multiple-output (MIMO) radar system, which includes the whole radar system parameters: geometric sensor configuration, waveforms, range, range rate, target scattering and noise characteristics. Recent research indicates the potential parameter estimate performance of bistatic MIMO radars. And this ambiguity function can be used to analyze the parameter estimate performance for the relationship with the Cramer-Rao bounds of the estimated parameters. Finally, some examples are given to demonstrate the good parameter estimate performance of the bistatic MIMO radar, using the quasi-orthogonal waveforms based on Lorenz chaotic systems.

Polarimetric PALSAR Calibration

Polarimetric Phased-Array-type L-band Synthetic Aperture Radar (PALSAR) system parameters are assessed using data sets collected over several calibration sites. The data collected over the Amazonian rain forest help validate the hypothesis that Faraday rotation is zero near the equator. The analysis of the Amazonian forest data and the response of the corner reflectors deployed there during the PALSAR acquisitions lead to the conclusion that the antenna is highly isolated (better than -35 dB). These results are confirmed using the data collected over calibration sites located in Sweden and Canada. The 5-m-height corner reflector deployed at the Remningstorp (Sweden) calibration site by Chalmers University of Technology provides accurate measurement of antenna parameters and detection of a (2deg -3deg) Faraday rotation during day-time acquisitions, whereas no Faraday rotation was noted during night-time acquisitions. Small Faraday rotation angles (2deg-3deg) have been measured using acquisitions over the DLR Oberpfaffenhofen and the Ottawa calibration sites. The presence of small but still significant Faraday rotation (2deg-3deg) induces a corner reflector return at the cross-polarization HV and VH that should not be interpreted as the actual antenna crosstalk. These results show that the PALSAR antenna is highly isolated (better than -35 dB), and diagonal antenna distortion matrices (with zero crosstalk terms) can be used for accurate calibration of PALSAR polarimetric data.