The Experts below are selected from a list of 3903 Experts worldwide ranked by ideXlab platform
Robert Wang - One of the best experts on this subject based on the ideXlab platform.
-
very high resolution sar imaging with dgps supported airborne x band data
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2020Co-Authors: Yashi Zhou, Yunkai Deng, Lei Zhang, Pei Wang, Zhen Chen, Qingchao Zhao, Wei Wang, Robert WangAbstract:High spatial resolution imaging in synthetic-aperture radar (SAR) can provide accurate monitoring capacity and has been gaining great attention recently in the fields of military and civilian. Apparently, the Slant Range resolution of the SAR system depends on the radar operating bandwidth. Currently, the large bandwidth signal synthesizing technology of the stepped frequency chirp signal waveform is highly practical for achieving high spatial resolution. However, the system structure and the corresponding signal processing technology become more complex. In order to verify the feasibility and operability of the large full-bandwidth system, a 3.6-GHz full-bandwidth airborne experimental SAR system operating at X-band, featured by full-bandwidth transmitting and receiving, has been designed by the Department of Space Microwave Remote Sensing System, Institute of Electronics, Chinese Academy of Sciences, as a test bed for the development and implementation of the future spaceborne realizations. For this large full-bandwidth SAR system, in addition to the hardware resource, the motion compensation (MOCO) is an urgent problem. The improvement of spatial resolution will aggravate the effect of motion errors. In order to focus the SAR images accurately, this article presents a technical approach by utilizing the differential global positioning system (DGPS) technology to improve the position accuracy of the inertial measurement unit device. Meanwhile, considering the significant deviation of Range cell migration correction (RCMC) due to the residual Range-variant errors, this article proposes an accurate MOCO strategy with DGPS-supported to implement the second-order MOCO, space-variant residual Range envelope, and space-variant residual phase error in azimuth before RCMC. Finally, this article presents the outfield experiment and reports the corresponding analysis and processing results of an outfield flight experiment successfully conducted in March 2019.
-
image formation processing for sliding spotlight sar with stepped frequency chirps
IEEE Geoscience and Remote Sensing Letters, 2014Co-Authors: Xiulian Luo, Yunkai Deng, Robert Wang, Yunhua Luo, Lei GuoAbstract:This letter extends the “two-step” focusing approach to sliding spotlight (SS) synthetic aperture radar (SAR) with stepped frequency chirps, where two major points should be looked out. One is the Slant-Range variation among one group of subpulses introduced by the radar platform position changing. In the stripmap mode, an effective approach to compensate this variation is to multiply each subband echo with a phase ramp in the Doppler domain. Herein, we apply this approach to the SS SAR. The other is the residual Doppler bandwidth after azimuth deramping with a fixed reference function. To remove this residual bandwidth, a Range-frequency-dependent reference function (FDRF) combined with azimuth zero-padding was developed in a spotlight SAR with a single subband. In this letter, we extend the FDRF to the multiple-subband SS SAR, where the FDRF also depends on the subband carrier frequency. The main contribution of this letter is that the chirp $z$ transform is employed to acquire an identical azimuth output pixel interval for different Range frequencies and different subbands. All the aforementioned processing and the bandwidth synthesis are imbedded into the “two-step” focusing approach, which is validated by simulation results.
-
model and signal processing of bistatic frequencymodulated continuous wave synthetic aperture radar
Iet Radar Sonar and Navigation, 2012Co-Authors: Robert Wang, O Loffeld, X WangAbstract:Bistatic frequency-modulated continuous wave (FMCW) synthetic aperture radar (SAR) mounts the radar transmitter and receiver on separate platforms, which offers considerable capabilities, reliability and flexibility in designing FMCW SAR missions. Moreover, the spatial separation achieves better isolation between transmission and reception channels compared with the monostatic FMCW SAR where the two separate dedicated antennas are fixed on one platform. In this study, a bistatic FMCW SAR signal model is proposed to formulate the bistatic Slant Range history in bistatic FMCW configuration. Based on the preceding model, an approach is presented to deal with the double-square-root (DSR) term, and thus an accurate FMCW bistatic point target reference spectrum (BPTRS) is derived. Besides accurately addressing the signal characteristics of bistatic FMCW SAR, the proposed spectrum also significantly simplifies the signal processing of bistatic FMCW SAR, which will really push the applications of bistatic FMCW SAR in remote sensing fields. Furthermore, based on the proposed BPTRS, an extended inverse chirp-Z transform (EICZT) algorithm is proposed to process the bistatic FMCW SAR data by introducing a perturbation function to deal with the Range-variance of second- and third-order Range-azimuth coupling terms. Two simulation experiments are carried out to verify the accuracy of this novel formulation and highlight the performance of the proposed focusing approach.
-
Focus Squint FMCW SAR Data Using Inverse Chirp-Z Transform Based on an Analytical Point Target Reference Spectrum
IEEE Geoscience and Remote Sensing Letters, 2012Co-Authors: Yue Liu, Yunkai Deng, Robert WangAbstract:Frequency-modulated continuous-wave (FMCW) synthetic aperture radar (SAR) systems offer smaller size and lower cost compared with pulsed-mode systems. They are therefore widely used for Earth observation where frequent revisits at low costs or small sizes are desirable. By accurately formulating the instantaneous Slant Range during the transmitting and receiving operations, an analytical point target reference spectrum has been developed for the FMCW SAR system, where an additional Range-azimuth coupling term is found. Based on previous work, this letter presents a modified inverse chirp-Z transform (ICZT) algorithm to deal with the Range-azimuth coupling term, which appears to be a scaling factor in Range. The new scaling factor is formulated in this letter for the first time. An ICZT is well suited for FMCW SAR since it can handle a dechirped signal without interpolations, thus reducing the computing load. Simulation experiment and real data processing result validate the proposed focusing algorithm.
-
frequency domain bistatic sar processing for spaceborne airborne configuration
IEEE Transactions on Aerospace and Electronic Systems, 2010Co-Authors: Robert Wang, Otmar Loffeld, Holger Nies, S Knedlik, Q Ulann, A Medranoortiz, Joachim H G EnderAbstract:This paper focuses on the bistatic synthetic aperture radar (BiSAR) signal processing in the spaceborne/airborne configuration. Due to the extreme differences in platform velocities and Slant Ranges, the airborne system operates in the inverse sliding spotlight mode, while the spaceborne system works in the sliding spotlight mode to achieve a tradeoff between the azimuth scene size and azimuth resolution. Such a mode is generally called double sliding spotlight mode. In this configuration, the echoed signal has two characteristics. Firstly, both transmitter and receiver have very short synthetic aperture times. Secondly, the airborne platform operates with wide squint difference, while the spaceborne platform works in the small squint case. According to these two features, we use different Taylor expansions to address the Slant Range histories of transmitter and receiver. Based on the presented model, a two-dimensional space-variant bistatic point target reference spectrum (BPTRS) is derived. Furthermore, we linearize the BPTRS to derive the transfer function of the baseband scene. From the transfer function, the signal features of the spaceborne/airborne configuration become very clear. Using the transfer function, the two-dimensional inverse scaled Fourier transform (ISFT) is used to focus the bistatic signal in the spaceborne/airborne configuration.
Mengdao Xing - One of the best experts on this subject based on the ideXlab platform.
-
robust clutter suppression and moving target imaging approach for multichannel in azimuth high resolution and wide swath synthetic aperture radar
IEEE Transactions on Geoscience and Remote Sensing, 2015Co-Authors: Shuangxi Zhang, Mengdao XingAbstract:This paper describes a clutter suppression approach and the corresponding moving target imaging algorithm for a multichannel in azimuth high-resolution and wide-swath (MC-HRWS) synthetic aperture radar (SAR) system. Incorporated with digital beamforming processing, MC-HRWS SAR systems are able to suppress the Doppler ambiguities to allow for HRWS SAR imaging and null the clutter directions to suppress clutter for ground moving target indication. In this paper, the degrees of freedom in azimuth for the multichannel SAR systems are employed to implement clutter suppression. First, the clutter and moving target echoes are transformed into the Range compression and azimuth chirp Fourier transform frequency domain, i.e., coarse-focused images formation, when the clutter echoes are with azimuth Doppler ambiguity. Considering that moving targets are sparse in the imaging scene and that there is a difference between clutter and a moving target in the spatial domain, a series of spatial domain filters are constructed to extract moving target echoes. Then, using an extracted moving target echo, two groups of signals are formed, and Slant-Range velocity of a moving target can be estimated based on baseband Doppler centroid estimation algorithm and multilook cross-correlation Doppler centroid ambiguity number resolving approach. After the linear Range cell migration correction and azimuth focus processing, a well-focused moving target image can be obtained. In addition, the proposed clutter suppression and imaging approach is not only adapted for uniformly displaced phase center sampling but also for the nonuniform sampling cases. Some simulation experiments are taken to demonstrate our proposed algorithms. Finally, some real measured data results are presented to validate the theoretical investigations and the proposed approaches.
-
a 2 d space variant chirp scaling algorithm based on the rcm equalization and subband synthesis to process geosynchronous sar data
IEEE Transactions on Geoscience and Remote Sensing, 2014Co-Authors: Mengdao Xing, Yong Wang, Jun YangAbstract:A space-variant chirp scaling algorithm based on the Range cell migration (RCM) equalization and azimuth subband synthesis has been studied to process simulated geosynchronous synthetic aperture radar (GEO-SAR) data. The acceptable order of terms in polynomials for the Slant Range models in the RCM correction and phase error compensation, division of subband, and suppression of grating lobes of the subbands was investigated. Qualitatively and quantitatively, the method was able to focus simulated GEO-SAR signals well. Finally, the constraint on the spatial extent of azimuth and Range dimensions using the algorithm was assessed.
-
focusing parallel bistatic sar data using the analytic transfer function in the wavenumber domain
IEEE Transactions on Geoscience and Remote Sensing, 2007Co-Authors: Zhenhua Zhang, Mengdao Xing, Jinshan DingAbstract:In recent years, bistatic synthetic aperture radar (BiSAR) has attracted the attention of many radar researchers. It is well known that the Slant Range history of BiSAR is the sum of two square-rooted terms, which correspond to the transmitting and receiving Slant Ranges, respectively. For a point target in the SAR scene, it is quite difficult, if not impossible, to obtain an analytic formula to describe the target echo data in the 2-D frequency domain without any approximation by using the conventional stationary phase method, which makes it very difficult to develop fast-focusing algorithms for BiSAR. In this paper, based on the concept of an instantaneous Doppler wavenumber and by defining a new variable called half quasi-bistatic angle, an analytic formula of the point target response in the spectral domain is developed for BiSAR with parallel trajectory (referred to as parallel BiSAR for simplicity). Relying on a first-order Taylor expansion of the above formula with respect to the parameter called the sum of closest distances on the swath center, a bistatic Range migration algorithm is proposed for any azimuth-shift-invariant BiSAR data processing. Simulation results have confirmed the effectiveness of the proposed novel approach.
F. Perez-martinez - One of the best experts on this subject based on the ideXlab platform.
-
On the Doppler Spreading Effect for the Range-Instantaneous-Doppler Technique in Inverse Synthetic Aperture Radar Imagery
IEEE Geoscience and Remote Sensing Letters, 2010Co-Authors: J. M. Munoz-ferreras, F. Perez-martinezAbstract:Inverse synthetic aperture radar (ISAR) is an all-weather radar technique which may generate high-resolution images of noncooperative targets. The standard Range-Doppler algorithm (RDA) is usually employed for image generation. However, the images obtained with RDA are usually blurred because of the relative motion between radar and target. As a consequence, motion compensation techniques should be used to improve the imagery quality. The Range-instantaneous-Doppler (RID) technique based on time-frequency transforms has been proposed for obtaining a sequence of focused ISAR images without the need of using motion compensation techniques. However, in this letter, it is clearly shown that the migration of the target scatterers in Slant Range indirectly induces Doppler spreading of the scatterers' point spread function in each of the ISAR images obtained by the RID technique. This Doppler spreading means blurring. It is important to highlight that the migration in Slant Range may be caused not only by the radial component of the translational motion but also by the rotational motion. The application of motion compensation techniques prior to the use of the RID technique allows us to mitigate the Doppler spreading, as shown here both for simulated and live data acquired by a high-resolution coherent radar.
-
Non-uniform rotation rate estimation for ISAR in case of Slant Range migration induced by angular motion
IET Radar Sonar & Navigation, 2007Co-Authors: José-maría Muñoz-ferreras, F. Perez-martinezAbstract:Target rotation is the desired motion to obtain descriptive inverse synthetic aperture radar images. However, it can generate blurring effects: the migration through resolution cells. This blurring is more severe when the rotation rate is non-uniform. A method to estimate the non-uniform rotation rate (second-order model) for non-cooperative targets is addressed here. The technique considers the possibility of existence of Slant Range migration induced by angular motion, unlike other approaches. It needs a previous estimation of the Range and radial velocity of two prominent points at two instants and minimises a function in order to estimate the motion parameters, which are used to polar format the radar data. The method is compared with the moving target imaging algorithm of Werness et al. and a time – frequency based technique. Simulated data are used to verify the approach and make the comparisons.
Jesús Ballestrín - One of the best experts on this subject based on the ideXlab platform.
-
Sensitivity study for modelling atmospheric attenuation of solar radiation with radiative transfer models and the impact in solar tower plant production
Solar Energy, 2016Co-Authors: Jesús Polo, Jesús Ballestrín, Elena CarraAbstract:Abstract The solar radiation reflected by the heliostats towards the receiver in solar tower plants may be attenuated by scattering and absorption processes along the optical path. This phenomenon has been traditionally computed by the solar tower plant codes using simple models based on polynomial functions of the Slant Range and taking very extreme conditions for the turbidity based on the standard visual Range. Radiative transfer codes (libRadtran) allow modelling the atmospheric attenuation as a function of the Slant Range considering different aerosol conditions taken from several AERONET stations in regions of interest for CSP. The methodology presented in this work for modelling atmospheric attenuation with libRadtran can be used with any other radiative transfer model. The results showing the sensitivity of the attenuation loss to the aerosol optical depth, assuming homogeneous vertical distribution, have been fit to a simple model that can be used in Solar Advisor Model (SAM). The attenuation loss in the model proposed reaches around 20% at 1 km of Slant Range for highly aerosol load typical of some desert sites. Sensitivity estimations with SAM have been performed also for two reference solar tower plants (Ivanpah 1 and Gemasolar) to study the impact of atmospheric attenuation in the output power of the plant. The different attenuation loss between low and very high turbidity conditions can result in a reduction of the power output of a large plant like Ivanpah 1 of around 12% of average daily production, 20% in the field optical efficiency and 11% in the power absorbed by the receiver. In smaller plants with large thermal storage system (Gemasolar) the impact of the attenuation loss is significantly smaller (around 4%). Modelling the atmospheric attenuation in the solar tower codes should include aerosol optical depth as input in a daily basis for allowing the inclusion of the expected aerosol variability of desert and arid sites.
-
solar radiation attenuation in solar tower plants
Solar Energy, 2012Co-Authors: Jesús Ballestrín, Aitor MarzoAbstract:Abstract With the advent of the first commercial solar power tower plants with a rated power in the 10–20 MW Range, scale-up to larger 20–50 MW commercial plants is being considered ( Lata et al., 2010 , Herring, 2009 ) in the vast arid regions of the sunbelt. In the case of single-tower plants, the heliostat field size grows considerably and the heliostat–receiver Slant Range distances are often over 1 km. Solar radiation attenuation over these distances cannot be neglected and must be taken into consideration during plant design. The measurement of the atmospheric attenuation is not an easy task and the use of spectral atmospheric transmission models is necessary. We used the MODTRAN (MODerate resolution atmospheric TRANsmission) code to study the solar radiation attenuation at different Slant Range distances in different scenarios: rural atmosphere on a clear day (visibility 23 km) and rural atmosphere on a hazy day (visibility 5 km).
Joachim H G Ender - One of the best experts on this subject based on the ideXlab platform.
-
frequency domain bistatic sar processing for spaceborne airborne configuration
IEEE Transactions on Aerospace and Electronic Systems, 2010Co-Authors: Robert Wang, Otmar Loffeld, Holger Nies, S Knedlik, Q Ulann, A Medranoortiz, Joachim H G EnderAbstract:This paper focuses on the bistatic synthetic aperture radar (BiSAR) signal processing in the spaceborne/airborne configuration. Due to the extreme differences in platform velocities and Slant Ranges, the airborne system operates in the inverse sliding spotlight mode, while the spaceborne system works in the sliding spotlight mode to achieve a tradeoff between the azimuth scene size and azimuth resolution. Such a mode is generally called double sliding spotlight mode. In this configuration, the echoed signal has two characteristics. Firstly, both transmitter and receiver have very short synthetic aperture times. Secondly, the airborne platform operates with wide squint difference, while the spaceborne platform works in the small squint case. According to these two features, we use different Taylor expansions to address the Slant Range histories of transmitter and receiver. Based on the presented model, a two-dimensional space-variant bistatic point target reference spectrum (BPTRS) is derived. Furthermore, we linearize the BPTRS to derive the transfer function of the baseband scene. From the transfer function, the signal features of the spaceborne/airborne configuration become very clear. Using the transfer function, the two-dimensional inverse scaled Fourier transform (ISFT) is used to focus the bistatic signal in the spaceborne/airborne configuration.
-
chirp scaling algorithm for bistatic sar data in the constant offset configuration
IEEE Transactions on Geoscience and Remote Sensing, 2009Co-Authors: Robert Wang, Otmar Loffeld, Holger Nies, S Knedlik, Joachim H G EnderAbstract:This paper discusses the processing method for bistatic SAR data in the constant-offset configuration. The constant-offset configuration is also known as the azimuth stationary or invariant configuration where transmitter and receiver follow each other, moving on identical velocity vector. In this paper, the proposed processing method for bistatic SAR data is based on Loffeld's bistatic formula that consists of two terms, i.e., the quasi-monostatic (QM) term and bistatic-deformation (BD) term. Our basic idea is to linearize the aforementioned two terms and then incorporate the BD term into the QM term to obtain an analogous monostatic spectrum. Based on the new spectrum, any efficient 2-D frequency or Range-Doppler domain processor can easily be employed to process the bistatic data, where the Doppler phase parameters of the processor need to be adjusted. In this paper, we concentrate on the application of chirp-scaling-algorithm (CSA) processor. In addition, a bistatic-motion error model is developed where the position deviations of the two platforms are simplified as the bistatic Slant-Range displacement in the zero Doppler plane. Using this model, the monostatic motion-compensation technique is applied and integrated into CSA to compensate the trajectory deviations of transmitter and receiver. Finally, real and simulated data are used to validate the proposed processing method.