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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Flood-Area Detection Using Palsar-2 Data for Heavy Rainfall Disasters in Japan
摘要： Rapid and all-weather detection of flood areas is needed for monitoring and mitigating flood disasters. In this paper, we investigated flood area detection using ALOS-2 PALSAR-2 data acquired during the 2015 heavy rainfall disaster in the Kanto and Tohoku areas, Japan. We detected flood areas by thresholding amplitude images from PALSAR-2 and then evaluated their accuracies against inundation maps based on aerial photographs. The highest accuracy was a 0.583 kappa coefficient in flood/non-flood discrimination. Our comparative study results indicate that lower off-nadir angles (around 30 degrees or less) are effective in the detection of flood areas. We also found polarimetric analysis and speckle filtering to be effective in improving accuracy. The results of this study demonstrate the feasibility of using PALSAR-2 data for rapid flood monitoring and as a reference for future flood disasters.
关键词： radar polarimetry,disaster monitoring,image processing,ALOS-2,synthetic aperture radar
更新于2025-09-09 09:28:46
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Extended Geometrical Perturbation Based Detectors for PolSAR Image Target Detection in Heterogeneously Patched Regions
摘要： Target detection in synthetic aperture radar image utilizing polarimetric information has attracted considerable attention. Single-target detector (STD), partial-target detector (PTD), and geometrical perturbation-polarimetric notch filter (GP-PNF) are three traditional polarimetric detectors based on polarimetric information. STD aims at detecting single targets, whereas PTD is suitable for partial targets. GP-PNF focuses on detecting targets with features, which are different from the homogeneous background. Both STD and PTD need a prior knowledge of the target, whereas GP-PNF needs to estimate the local clutter automatically. All these three methods use a feature vector to describe the character of the target or clutter. In fact, the feature vectors of the clutter and target may distribute in a subspace. Especially for the heterogeneous background, a feature vector cannot accurately describe the clutter. Motivated by this, this paper extends the clutter model from a complex feature vector to a complex feature subspace, which is suitable for a heterogeneously patched region and derives extended PTD and extended GP-PNF. Experimental results show the extended detectors’ validation and superiority to traditional detectors for target detection in heterogeneous regions.
关键词： Heterogeneous region,radar polarimetry,synthetic aperture radar (SAR),target detection
更新于2025-09-09 09:28:46
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Unsupervised Change Detection in Polarimetric SAR Data With the Hotelling-Lawley Trace Statistic and Minimum-Error Thresholding
摘要： Increased discrimination capability provided by polarimetric synthetic aperture radar (PolSAR) sensors compared to single and dual polarization synthetic aperture radar (SAR) sensors can improve land use monitoring and change detection. This necessitates reliable change detection methods in multitemporal PolSAR datasets. This paper proposes an unsupervised change detection algorithm for multilook PolSAR data. In the first step of the method, the Hotelling-Lawley trace (HLT) statistic is applied to measure the similarity of two multilook covariance matrices. As a result of this step, a scalar test statistic image is generated. Then, in the second step, a generalized Kittler and Illingworth (K&I) minimum-error thresholding algorithm is developed to perform on the test statistic image and discriminate between changed and unchanged areas. The K&I thresholding algorithm is based on the generalized Gamma distribution for statistical modeling of change and no-change classes. The proposed methodology is tested on a simulated PolSAR data and two C-band fully PolSAR datasets acquired by the uninhabited aerial vehicle SAR and RADARSAT-2 SAR satellites. The experiments show that the proposed algorithm accurately discriminates between change and no-change areas providing detection results with noticeably lower error rates and higher detection accuracy values compared to those of a CFAR-type thresholding of the HLT statistic. Also, the performance of the HLT statistic compared to the other statistics applied on the multilook polarimetric SAR data is assessed. Goodness-of-fit test results prove that the estimated generalized Gamma class conditional models adequately fit the corresponding change and no-change classes.
关键词： illingworth thresholding,minimum-error kittler,Change detection,polarimetric synthetic aperture radar (PolSAR),hotelling-lawley trace (HLT) statistic
更新于2025-09-09 09:28:46
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Multifrequency Polarimetric SAR Image Despeckling by Iterative Nonlocal Means Based on a Space-Frequency Information Joint Covariance Matrix
摘要： This paper presents an iterative nonlocal means (NLM) filtering method under the Bayesian framework to deal with the issue of multifrequency fully polarimetric synthetic aperture radar (PolSAR) image despeckling. Differing from most of the PolSAR filters designed for single-frequency data, the proposed NLM method is developed based on a space-frequency information joint covariance matrix, which can not only utilize multifrequency polarimetric information but also exploit the correlation between any two pixels in an image patch. Furthermore, with the aim of accelerating the filtering procedure and better retaining image details, an effective preselection step is employed. The filtering results obtained with both a simulated dataset and real multifrequency PolSAR datasets acquired by the AIRSAR system confirm the good performance of the proposed method in both reducing speckle and retaining details, when compared with some of the state-of-the-art despeckling algorithms.
关键词： Nonlocal means (NLM),polarimetric synthetic aperture radar (PolSAR),speckle filtering,Wishart distribution
更新于2025-09-09 09:28:46
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A New Azimuth Ambiguity Suppression Algorithm for Surface Current Measurement in Coastal Waters and Rivers With Along-track InSAR
摘要： We present a new algorithm for suppressing azimuth ambiguities when measuring surface currents with an along-track interferometric (ATI) synthetic aperture radar in heterogeneous scenes, such as coastal waters or rivers. The key of the proposed algorithm involves a careful analysis of a parameter called the eigenvalue spectrum entropy (EVSE), which is defined as the entropy of the eigenvalue spectrum of the ATI covariance matrix computed in the Doppler domain. The physical meaning of EVSE is that it serves as a descriptor for the degree to which an unambiguous signal component and an ambiguous one are mixed. With the help of EVSE, azimuth ambiguities can be suppressed. Simulation results demonstrate that as compared with the conventional ATI method without azimuth ambiguity suppression, the proposed algorithm allows for a pronounced improvement in the current measuring accuracy. Other advantages of the proposed algorithm lie in the fact that it is not only adaptive, due to its ability to automatically capture the useful Doppler band whose width and position may both vary for different radar and scene parameters, but it also needs a minimal number of user inputs, making it a quite attractive algorithm for routine implementation.
关键词： eigenvalue spectrum entropy (EVSE),current retrieval,surface currents in rivers,ocean surface currents,azimuth ambiguities,Along-track interferometric (ATI) synthetic aperture radar (SAR)
更新于2025-09-09 09:28:46
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A Novel Azimuth Cutoff Implementation to Retrieve Sea Surface Wind Speed From SAR Imagery
摘要： In this paper, the synthetic aperture radar (SAR) azimuth cutoff method is thoroughly revised and a new and general implementation is proposed. The key roles of the pixel spacing, the size of the image box, and the texture of the SAR scene are analyzed and optimized in terms of azimuth cutoff (λc) estimation. The reliability of the λc estimation is analyzed by measuring the distance between the measured and ?tted autocorrelation functions. This analysis shows that it is of paramount importance to ?lter unfeasible/unreliable λc values. To identify those values in an objective way, a criterion that is based on the χ2 test performed over a large data set of Sentinel-1 SAR imagery is de?ned and proven to be effective. The new robust implementation of the λc estimation at about 1-km grid spacing is then used to produce averaged λc at about 10-km grid spacing. The performance of the new estimation procedure, analyzed using a λc-to-wind-speed forward model, is shown to provide improved wind speed retrievals, with a root-mean-square error of 1.8–2 m/s when veri?ed against independent numerical weather prediction model output and scatterometer winds.
关键词： sea surface,spectral analysis,synthetic aperture radar,Cutoff frequency
更新于2025-09-09 09:28:46
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Two-Stage Beamforming for Phased Array Imaging using the Fast Hankel Transform
摘要： An ultrasound scan generates a huge amount of data. To form an image this data has to be transferred to the imaging system. This is an issue for applications where the data transfer capacity is limited such as hand-held systems, wireless probes and miniaturized array probes. Two-stage beamforming methods can be used to significantly reduce the data transfer requirements. In the first stage, which is applied in-probe, the amount of data is reduced from channel to scanline data. In the imaging system the data is then beamformed to obtain images that are synthetically focused over the entire image. Currently two approaches exist for the second stage. The first approach is a time-of-flight approach called synthetic aperture sequential beamforming (SASB) that has been developed for both linear and phased arrays. SASB does however introduce artefacts in the image that can be reduced by tapering the first stage scan lines at the cost of lateral resolution. The second approach is based on the wave equation, but a computationally efficient method for phased arrays that is producing sector scan data is lacking. Here we propose an algorithm that uses the fast Hankel transform to obtain a fast algorithm. The imaging performance of this method is evaluated with simulations and experiments. Compared with PSASB, which is an adaption of SASB for phased arrays, our method requires a similar amount of operations to construct the entire image and there is no trade-off between resolution and artefacts. These results show the advantage of using the wave equation instead of a time-of-flight approach.
关键词： Ultrasound imaging,two-stage beamforming,synthetic aperture,phased array,migration
更新于2025-09-09 09:28:46
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Interferometric Angular Decorrelation Analysis of 1-D Rough Surface With Pencil Beam Incidence
摘要： Interferometric synthetic aperture radar (InSAR) uses phase difference of radar echoes, either from multiple passes along the same trajectory or from multiple displaced phase centers on a single pass, to generate interferogram. Scattering correlation in the angular dimension is a critical factor determining the quality of InSAR interferogram. It can be modeled with the angular correlation function (ACF). In this letter, the ACF of a 1-D rough surface under incidence of a tapered wave, namely, a pencil beam, is studied numerically for correlation analysis of InSAR. An analytic ACF is ?rst derived based on the ?rst-order small perturbation method. It is then validated statistically by the method of moment of electromagnetic scattering. Analysis of the ACF simulations indicate that the ACF of backscattering from a randomly rough surface exhibits a shape of sinc function, which depends on tapering parameter g, interferometric incidence angles θ1 and θ2. Several numerical simulations of different rough surface spectrums demonstrate that the analytical ACF ?ts well with numerical results as long as g is the larger several correlation lengths l.
关键词： interferometric synthetic aperture radar (InSAR),Angular correlation function (ACF),small perturbation method (SPM),surface roughness
更新于2025-09-09 09:28:46
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Comparison of the Rayleigh and K-Distributions for Application in Incoherent Change Detection
摘要： The aim of this letter is to compare two incoherent change-detection algorithms for target detection in low-frequency ultrawideband (UWB) synthetic aperture radar (SAR) images. The considered UWB SAR operates in the frequency range from 20 to 90 MHz. Both approaches employ a likelihood ratio test according to the Neyman–Pearson criterion. First, the bivariate Rayleigh probability distribution is used to implement the likelihood ratio test function. This distribution is well known and has been used for change-detection algorithms in low-frequency UWB SAR with good results. Aiming to minimize the false alarm rate and taking into consideration that low-frequency UWB SAR images have high resolution compared to the transmitted wavelength, the second approach implements the test by using a bivariate K-distribution. This distribution has scale and shape parameters that can be used to adjust it to the data. No ?lter is applied to the data set images, and the results show that with a good statistical model, it is not needed to rely on ?ltering the data to decrease the number of false alarms. Therefore, we can have a better tradeoff between resolution and detection performance.
关键词： likelihood ratio test,synthetic aperture radar (SAR),Change detection
更新于2025-09-09 09:28:46
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IMAGE FORMATION USING FAST FACTORIZED BACKPROJECTION BASED ON SUB-APERTURE AND SUB-IMAGE FOR GENERAL BISTATIC FORWARD-LOOKING SAR WITH ARBITRARY MOTION
摘要： In this paper, a fast time domain imaging algorithm called bistatic forward-looking fast factorized backprojection algorithm (BF-FFBPA) based on sub-aperture and sub-image is proposed for general bistatic forward-looking synthetic aperture radar (BFSAR) with arbitrary motion. It can not only accurately dispose the large spatial variant range cell migrations and complicated motion errors, but also achieve high imaging e?ciency. First, the imaging geometry and signal model are established, and the implementation of back projection algorithm (BPA) in the BFSAR imaging is given to provide a basis for the proposed BF-FFBPA. Then, considering motion errors, the more accurate requirements of splitting sub-aperture and sub-image in the BF-FFBPA is introduced based on the range error analysis to o?er the tradeo? between the imaging quality and e?ciency. Finally, the implementation and computational burden of the BF-FFBPA is provided and analyzed. Simulated results and evaluations are given to prove the correctness of the theory analysis and the validity of the proposed approach.
关键词： arbitrary motion,bistatic forward-looking synthetic aperture radar (BFSAR),sub-image,fast factorized backprojection algorithm (FFBPA),sub-aperture
更新于2025-09-04 15:30:14