Sidelobe Effects Research Articles

Novel Orthogonal Random Phase-Coded Pulsed Radar for Automotive Application

In contrast to remote sensing radar, automotive radar focuses on the detection of short-range targets in the 0–1000 m range. Conventional automotive pulsed radar usually uses a monostatic antenna and it requires high peak power for the transmission of the short duration pulses to reliably detect targets at close range with a high resolution. Unfortunately, it is difficult and expensive to generate high-powered pulses on the nanosecond scale. Meanwhile, the existing automotive radars suffer from bottlenecks, i.e., spatial resolution, sidelobe levels, and Inter-Sensor Interference (ISI). To overcome the above challenges, a bistatic antenna to transmit and receive large time-bandwidth product waveforms is firstly proposed in this paper. Secondly, high spatial resolution is implemented using a Digital Beam Forming (DBF) transmitter and the high range resolution is achieved by using the pulse compression technique. Additionally, the radial velocity of the target is calculated by applying pulse Doppler processing. Finally, to deal with the sidelobe effect of impulse response function of point target and the interference arising from neighboring radars, novel Orthogonal Random Phase-Coded (ORPC) radar signals are presented. Using these ORPC signals, the impulse response function of the radar can achieve a peak sidelobe ratio of –45 dB without any loss in the signal-to-noise ratio. Most importantly, interference can be significantly reduced by using the proposed signals. Extensive simulations demonstrate the effectiveness and advantages of the proposed radar.

Ultra-wideband FMCW ISAR imaging with a large rotation angle based on block-sparse recovery

Ultra-wideband frequency modulated continuous wave (FMCW) radar has the ability to achieve high-range resolution. Combined with the inverse synthetic aperture technique, high azimuth resolution can be realized under a large rotation angle. However, the range-azimuth coupling problem seriously restricts the inverse synthetic aperture radar (ISAR) imaging performance. Based on the turntable model, traditional match-filter-based, range Doppler algorithms (RDAs) and the back projection algorithm (BPA) are investigated. To eliminate the sidelobe effects of traditional algorithms, compressed sensing (CS) is preferred. Considering the block structure of a signal at high resolution, a block-sparsity adaptive matching pursuit algorithm (BSAMP) is proposed. By matching pursuit and backtracking, a signal with unknown sparsity can be recovered accurately by updating the support set iteratively. Finally, several experiments are conducted. In comparison with other algorithms, the results from processing the simulation data, some simple targets, and a complex target indicate the effectiveness and superiority of the proposed algorithm.

Application of Artificial Neural Networks to Ship Detection from X-Band Kompsat-5 Imagery

For ship detection, X-band synthetic aperture radar (SAR) imagery provides very useful data, in that ship targets look much brighter than surrounding sea clutter due to the corner-reflection effect. However, there are many phenomena which bring out false detection in the SAR image, such as noise of background, ghost phenomena, side-lobe effects and so on. Therefore, when ship-detection algorithms are carried out, we should consider these effects and mitigate them to acquire a better result. In this paper, we propose an efficient method to detect ship targets from X-band Kompsat-5 SAR imagery using the artificial neural network (ANN). The method produces the ship-probability map using ANN, and then detects ships from the ship-probability map by using a threshold value. For the purpose of getting an improved ship detection, we strived to produce optimal input layers used for ANN. In order to reduce phenomena related to the false detections, the non-local (NL)-means filter and median filter were utilized. The NL-means filter effectively reduced noise on SAR imagery without smoothing edges of the objects, and the median filter was used to remove ship targets in SAR imagery. Through the filtering approaches, we generated two input layers from a Kompsat-5 SAR image, and created a ship-probability map via ANN from the two input layers. When the threshold value of 0.67 was imposed on the ship-probability map, the result of ship detection from the ship-probability map was a 93.9% recall, 98.7% precision and 6.1% false alarm rate. Therefore, the proposed method was successfully applied to the ship detection from the Kompsat-5 SAR image.

Refined segmentation of ship target in SAR images based on GVF snake with elliptical constraint

ABSTRACTOcean surveillance is an important application of synthetic aperture radar (SAR) image interpretation. In the ocean, the ship target usually attracts the attention of researchers, hence many interpretation works focus on it. The precise ship segmentation can facilitate further processing, such as feature extraction and target recognition. This paper proposes a refined segmentation method for ship target, in which the ratio of exponentially weighted averages (ROEWA) operator is used to produce the edge map and the elliptical constraint (EC) is incorporated into the energy function of the gradient vector flow (GVF) snake model to extract the ship target precisely. With this prior shape constraint, the snake contour can overcome unexpected distortions stemming from speckle noise and side lobe effect, etc. experimental results based on TerraSAR X-band and RADARSAT-2 C-band data illustrate the effective performance of the proposed method on refined segmentation for ship targets.

Detection of weak maneuvering target based on keystone transform and matched filtering process

Detection of weak maneuvering target often suffers from the problems of the range migration (RM) and the Doppler frequency migration (DFM) within the coherent pulse interval. In order to eliminate the RM and DFM, a new coherent integration method based on keystone transform (KT) and matched filtering process (MFP), i.e., KT-MFP, is proposed. Specifically, this method firstly corrects the linear RM caused by the unambiguous velocity via KT and then the MFP, which jointly searching in the fold factor and acceleration domain, is carried out to remove the residual RM and compensate the DFM. At last, coherent integration of the target’s energy is achieved through the slow time Fourier transform (FT). The advantage of the proposed method is that it can obtain superior coherent integration and detection performance for both the slow-moving and fast-moving target, in comparison with the existing algorithms. In addition, KT-MFP could avoid the blind speed sidelobe (BSSL) effect. Numerical simulations are performed to assess the performance from different aspects, i.e., computational complexity, coherent integration for a low-speed target, detection performance for a low-speed target, coherent integration for a high-speed target, detection performance for a high-speed target and coherent integration for multi-targets.

Saturated two-photon excitation fluorescence microscopy with core-ring illumination.

We demonstrated resolution improvement in two-photon excitation microscopy by combining saturated excitation (SAX) of fluorescence and pupil manipulation. We theoretically estimated the resolution improvement and the sidelobe effect in the point spread function with various pupil designs and found that the combination of SAX and core-ring illumination can effectively enhance the spatial resolution in 3D and suppress sidelobe artifacts. The experimental demonstration shows that the proposed technique is effective for observation with a depth of 100μm in a tissue phantom and can be applied to 3D observations of tissue samples with higher spatial resolution than conventional two-photon excitation microscopy.

Using instantaneous frequency and colored inversion attributes to distinguish and determine the sandstones facies of the Late Ordovician Mamuniyat reservoir, R-field in Murzuq Basin, Libya

The Mamuniyat petroleum reservoir in southwestern Libya is comprised of clean sandstones and intercalated shale and sand facies that are characterized by spatial porosity variations. Seismic reflection data from the field exhibit relatively low vertical seismic resolution, side lobes of reflection wavelets, reflection interference, and low acoustic impedance contrast between the reservoir and the units underneath the reservoir, which make mapping those facies a difficult task. In the absence of broadband seismic data, optimizing frequency bands of bandlimited data can be used to suppress pseudoreflectors resulting from side-lobe effects and help to separate the clean sandstone facies of the reservoir. We have optimized the data based on our investigation of seismic frequency bands and used instantaneous frequency analysis to reveal the reflection discontinuity that is mainly associated with the reservoir boundary of the sandstone facies of the clean Mamuniyat reservoir. We also preformed rock-physics diagnostic modeling and inverted the seismic data using spectral-based colored inversion into relative acoustic impedance. The inverted impedance matches the up-scaled impedance from the well data and the inversion of relative acoustic impedance confirms the conclusion that was drawn from the instantaneous frequency results. The interpretation of facies distributions based on the instantaneous frequency was supported by the inversion results and the rock-physics models.

Radar maneuvering target detection and motion parameter estimation based on TRT-SGRFT

In this paper, we address the detection and motion parameter estimation problem for a maneuvering target with complex motions, where range migration (RM, including range walk and range curvature) and Doppler frequency migration (DFM) occur during the coherent observation time. A method based on time reversing transform (TRT) and special generalized Radon Fourier transform (SGRFT), i.e., TRT-SGRFT, is proposed to achieve the detection and motion parameters estimation. More specifically, the TRT is firstly applied to separate the motion parameters and reduce the order of RM and DFM. Then the SGRFT operation is employed to estimate part of the motion parameters. After that, the residual motion parameters could be achieved via the second SGRFT operation. The advantage of the TRT-SGRFT algorithm is that it could avoid the blind speed sidelobe (BSSL) effect and obtain a good tradeoff between the computational cost and estimation performance, in comparison with generalized Radon Fourier transform. Several numerical experiments are provided to demonstrate the its effectiveness.

Information-Aided Smart Schemes for Vehicle Flow Detection Enhancements of Traffic Microwave Radar Detectors

For satisfactory traffic management of an intelligent transport system, it is vital that traffic microwave radar detectors (TMRDs) can provide real-time traffic information with high accuracy. In this study, we develop several information-aided smart schemes for traffic detection improvements of TMRDs in multiple-lane environments. Specifically, we select appropriate thresholds not only for removing noise from fast Fourier transforms (FFTs) of regional lane contexts but also for reducing FFT side lobes within each lane. The resulting FFTs of reflected vehicle signals and those of clutter are distinguishable. We exploit FFT and lane-/or time stamp-related information for developing smart schemes, which mitigate adverse effects of lane-crossing FFT side lobes of a vehicle signal. As such, the proposed schemes can enhance the detection accuracy of both lane vehicle flow and directional traffic volume. On-site experimental results demonstrate the advantages and feasibility of the proposed methods, and suggest the best smart scheme.

Angular two-point correlation of NVSS galaxies revisited

We measure the angular two-point correlation and angular power spectrum from the NRAO VLA Sky Survey (NVSS) of radio galaxies. They are found to be consistent with the best-fit cosmological model from the Planck analysis, and with the redshift distribution obtained from the Combined EIS-NVSS Survey Of Radio Sources (CENSORS). Our analysis is based on an optimal estimation of the two-point correlation function and makes use of a new mask, that takes into account direction dependent effects of the observations, sidelobe effects of bright sources and galactic foreground. We also set a flux threshold and take the cosmic radio dipole into account. The latter turns out to be an essential step in the analysis. This improved cosmological analysis of the NVSS emphasizes the importance of a flux calibration that is robust and stable on large angular scales for future radio continuum surveys.

The Application based on Fourier Transform in Time Lens

Using the similarity between the transmission of narrow band light pulses in the dispersion media and the transmission of spatial beam in paraxial diffraction, build a time lens system similar to the space lens. Space lens can achieve compression and amplification of imaging function, and it has the nature of Fourier transform in light field. Then the time lens can also realize the compression and amplification of the light pulse and its Fourier transform. Using the function of Fourier transform in the time domain of time lens system, achieved the effect of eliminating noise and removing side lobe, improved the white noise which generally exist in the communication system and the side lobe effect which will produce in the relevant processes.

Design and properties of Gaussian-type 1–3 piezoelectric composites

Here we developed three types of 1–3 connectivity piezoelectric composites consisting of the piezoelectric ceramic rods of gauss variation. The piezoelectric strain constant of the composites exhibits good gauss distribution along the length or radial directions of the composites. The electromechanical and acoustic properties of the piezoelectric composites are greatly improved. The kt value of the Gaussian area array composite is 65.02%, which increases by 30% compared with the piezoelectric ceramic. The acoustic impedance value of the composites with Gaussian linear array, Gaussian orthotropic linear array and Gaussian area array is 5.15, 4.74 and 5.93MRayl, respectively. Our work shows that the ultrasonic transducer which has broad bandwidth, good acoustic impedance matching ability and small acoustic beam side lobe effect can be achieved based on the proposed Gaussian piezoelectric composites.

Horizontal resolution of seismic acquisition geometries

      , , ,  , SUMMARY Spatial sampling has a crucial influence on the horizontal resolution of seismic imaging, but how to quantify the influence is still controversial especially in complex media. Most of the studies on horizontal resolution focus on the measurement of wavelet widths for seismic migration, but neglect to evaluate the effect of side-lobe perturbations on spatial resolution. The side-lobe effect, as a migration noise, is important for seismic imaging in complex media. In this article, with focal beam analysis, we define two parameters to represent the horizontal resolution of an acquisition geometry: the width of the main lobe (WML) along the inline and crossline directions and the ratio of the main-lobe amplitude to the total amplitude (RMT) in a focal beam. We provide examples of typical acquisition geometries to show that how spatial sampling affects the horizontal resolution, measured in terms of WML and RMT values. WML defines the horizontal resolution to image the target, whereas RMT describes the clarity of the imaging. Migration noise reduces with increasing RMT, indirectly improving both the vertical and horizontal resolutions of seismic imaging. Case studies of seismic migration with 3D seismic data demonstrate how the acquisition geometries with different WML and RMT values influence the performance of seismic imaging. A prior WML and RMT analysis to predict the quality of acquired datasets can optimize acquisition geometries before the implementation of seismic acquisition.

A low complexity coherent integration method for maneuvering target detection

This paper considers the coherent integration problem for detecting a maneuvering target with complex motions, where the velocity, acceleration and jerk result in respectively the range migration (RM), linear Doppler frequency migration (LDFM) and quadratic Doppler frequency migration (QDFM) within the coherent pulse interval. A new coherent integration algorithm based on keystone transform (KT) and generalized dechirp process (GDP), i.e., KTGDP, is proposed. In this method, KT and fold factor searching are first employed to correct the RM, and then GDP is applied to estimate the target's radial acceleration and jerk. With the estimated motion parameters, LDFM and QDFM can be compensated and the coherent integration can be achieved via Fourier transform. In addition, at the cost of some performance loss, a fast coherent integration method combing KT and cubic phase function (CPF), i.e., KTCPF, is also introduced to further reduce the computational complexity. Compared with the generalized Radon–Fourier transform (GRFT) method, the proposed algorithms can avoid the blind speed side lobe (BSSL) effect and have much lower computational burden. Finally, we evaluate the performance via some numerical simulations.

Improvement of sound source localization in a finite duct using beamforming methods

This paper presents work to identify the sound source location within a finite length duct with beamforming methods. Two types of problems were studied in this paper. First, the deconvolution approach for the mapping of acoustic sources (DAMAS) method is applied to minimize the side-lobe effects, and improve the spatial resolution at low frequencies. Second, the beamforming results may deteriorate when the sound frequency is close to the cut-on frequencies. In order to improve the results, an algorithm was developed. To validate the methods, both simulations and experiments were implemented. In the experiments, a synchronized system with forty-eight wall-mounted microphones in a finite length duct was established. The dependence of the azimuthal sound source localization and the planar sound source localization on the measurement frequency was studied. The results indicate that the accuracy of the localization is highly dependent on the number of the spinning modes that are able to propagate in the duct. The localization may fail when the frequency is close to the cut-on frequencies. Significant improvements can be achieved when DAMAS and the improved algorithm are implemented.

Motion detection improvement of a pencil-beam navigator echo using a gradient reversal technique

PurposeTo develop and demonstrate the feasibility of a pencil-beam navigator using a gradient reversal technique for reducing signal contamination from undesired excitation for precise motion detection and correction. Materials and methodsThe navigator echo was obtained using normal and reversed gradient waveforms sequentially in three-dimensional spoiled gradient-recalled echo imaging. These two signals were combined in the complex domain for generating the final navigator data, which were used for detecting the diaphragm motion to nullify the side lobe effects with the smallest radius from the beam center. The navigator signals were compared with and without the proposed technique in phantom and human scans. In addition, navigator-gated imaging was performed in the human scans. ResultsIn a phantom experiment, the proposed technique diminished signals from a phantom placed outside the beam’s area. In human scans, the proposed technique reduced undesired signals in the navigator data for all subjects. The resultant images had fewer motion-induced ghosts than the images from the conventional technique for 8 subjects out of 10. ConclusionsWe have demonstrated that the gradient reversal technique reduced undesired signals in a pencil-beam navigator. This technique can be an alternative for free-breathing abdominal scan when the conventional navigator technique cannot detect the patient’s respiratory motion precisely.

Effects of radar side-lobes on snow depth retrievals from Operation IceBridge

AbstractArctic snow depth data products from four years (2009–12) of Operation IceBridge (OIB) surveys are examined. In our analysis, we found spurious spikes in the snow depth distributions of both the multi-year and seasonal ice covers. These spikes are artifacts that stem from the incorrect identification of side lobes and main lobes of the impulse response of the snow radar as returns from the air–snow interface. The current OIB snow depth retrieval algorithm does not explicitly account for the presence of these side lobes and main lobes. As a result, overall accuracy of snow depth returns and related statistics is negatively affected. Although the range locations of these side lobes are predictable for each radar installation, they vary with individual airborne campaigns. Comparisons with limited in situ snow surveys show significant differences of >20 cm between OIB and in situ snow surveys. These artifacts affect OIB ice thickness estimates because they rely on estimates of sea-ice freeboard, which are calculated as the differences between coincident snow freeboard from lidar elevations and the retrieved snow depth estimates discussed here. Since these products are widely distributed to the scientific community, our results suggest that earlier geophysical studies based on these products may need to be re-examined.

ADCP 표층유속 자료처리방법 개선을 통한 영산강 하구 표층 방류수 이류속도 산정

It has been customary to exclude top 10-20% of velocity profiles in the Acoustic Doppler Current Profiler (ADCP) measurement due to side lobe effects at the boundary. To better understand the mixing in the Yeongsan estuary, the freshwater advection speed (FAS) was recovered from highly contaminated ADCP data near the surface. The velocity profiles were measured by using ADCP at two stations in the Yeongsan estuary during August 2011: one was located in front of the Yeongsan estuarine dam and the other was deployed near Goha Island. The FAS was recovered from the ADCP data set by applying rigorous post-processing methods and compared with the sediment advection speed (SAS). The SAS was determined by the peak time difference of suspended sediment concentration between two stations in the channel, divided by the distance of two stations. The FAS and the SAS showed very similar value when the freshwater discharge was greater than ton and the SAS was a bit greater when the freshwater discharge was smaller. Since the FAS was on average about 0.8 m/s greater than the velocity at 0.8 of water depth from the bottom, the net discharge, estimated with recovered FAS and integrated over water depth and tidal cycle, was directed seaward during the high discharge contrary to the onshore direction of the net discharge estimated with 0.8 of water depth from the bottom. Moreover, the velocity shear and Richardson number changed when the FAS was used. Thus, the importance of the true FAS is appreciated in the investigation of the surface layer stability. If currents, temperature and salinity were observed for longer time in the future, it could be possible to more accurately understand the formation and decay of stratification as well as the suspended sediment transport processes.

On horizontal resolution for seismic acquisition geometries in complex 3D media

Abstract Spatial sampling has a crucial influence on the horizontal resolution of seismic imaging, but how to quantify the influence is still controversial especially in complex media. Most of the studies on horizontal resolution focus on the measurement of wavelet widths for seismic migration, but neglect to evaluate the effect of side-lobe perturbations on spatial resolution. The side-lobe effect, as a migration noise, is important for seismic imaging in complex media. In this article, with focal beam analysis, we define two parameters to represent the horizontal resolution of an acquisition geometry: the width of the main lobe (WML) along the inline and crossline directions and the ratio of the main-lobe amplitude to the total amplitude (RMT) in a focal beam. We provide examples of typical acquisition geometries to show how spatial sampling affects the horizontal resolution, measured in terms of WML and RMT values. WML defines the horizontal resolution to image the target, whereas RMT describes the clarity of the imaging. Migration noise reduces with increasing RMT, indirectly improving both the vertical and horizontal resolutions of seismic imaging. Case studies of seismic migration with 3D seismic data from an oil field of China, demonstrate how the acquisition geometries with different WML and RMT values influence the performance of seismic imaging. Prior WML and RMT analyses to predict the quality of acquired datasets can optimize acquisition geometries before the implementation of seismic acquisition.

A New Method to Analyze Broadband Antenna-Radome Interactions in Time-Domain

Based on the new time-domain finite integration theorem (TDFIT), a fast and accurate method is proposed to analyze broadband antenna-radome interactions in time domain. Due to the time-domain feature, broadband characteristic is obtained in a single simulation. In numerical simulations, the antenna array is placed inside an enclosed or semi-closed radome by using a presented local waveguide port. The staircase error in traditional finite-difference time-domain method is reduced by a novel conformal technique. An illustrating broadband antenna array with radome, operating at millimeter wave frequency is analyzed and optimized to show the high performance of our method. A new broadband transmittance of the antenna-radome system is proposed to incorporate the side lobe effect, and it is treated as the objective function to optimize the parameters of the antenna-radome system. Furthermore, the full wave simulation, combined with an artificial neural network (ANN) algorithm, is utilized to accelerate the antenna-radome optimization. About half of the time for computation has been reduced.