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Geoscience and Remote Sensing Letters, IEEE

Issue 6 • Date Nov. 2011

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  • [Front cover]

    Publication Year: 2011 , Page(s): C1
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  • IEEE Geoscience and Remote Sensing Letters publication information

    Publication Year: 2011 , Page(s): C2
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  • Table of contents

    Publication Year: 2011 , Page(s): 1009 - 1010
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  • Preliminary Results of Superresolution-Enhanced Angular Hyperspectral (CHRIS/Proba) Images for Land-Cover Classification

    Publication Year: 2011 , Page(s): 1011 - 1015
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (736 KB) |  | HTML iconHTML  

    Superresolution (SR) image reconstruction is a technique to obtain a high-resolution (HR) image from a set of low-resolution images. Compact High Resolution Imaging Spectrometer (CHRIS)/Project for On-Board Autonomy (Proba) is a transitional hyperspectral-oriented satellite which acquires multiple angular images of the same scene. The angular images acquired within a very short period of time are ideal for SR operation. Recent developments point to the possibility of a SR-enhanced CHRIS data set at higher resolution. Apparently, the additional details are valuable information for many applications. This letter presents the preliminary evaluation of the SR CHRIS images for ecotope mapping and subpixel classification of sealed surface using two different scenes in Belgium. Accuracy obtained from SR CHRIS images is comparable to that of the original CHRIS, but with significantly more detail in the final classification map. In view of the demands for HR hyperspectral data sets, SR operation can be an interesting option to mitigate the lower spatial resolution of the current and future spaceborne hyperspectral images. Properties such as quick revisiting time and angular acquisition of a hyperspectral satellite are important for the success of SR operations. View full abstract»

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  • Correlation Coefficients Between Polarization Signatures for Evaluating Polarimetric Information Preservation

    Publication Year: 2011 , Page(s): 1016 - 1020
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (922 KB) |  | HTML iconHTML  

    In order to evaluate quantitatively the preservation performance of polarimetric information for polarimetric synthetic aperture radar (PolSAR) speckle filters, this letter presents correlation coefficients between the original and the filtered polarimetric data based on the theory of polarization synthesis. The copolarized and the cross-polarized correlation coefficients are furthermore discussed in cases whether the transmitting and receiving radar antennas are characterized by the same or orthogonal polarization state. To show how these coefficients can be exploited in evaluating the preservation of polarimetric information, they are demonstrated with a German Aerospace Center (DLR) Experimental Synthetic Aperture Radar L-band full-polarized image of the Oberpfaffenhofen Test Site Area (DE), Germany, which was obtained on September 30, 2000. Results make evident that the correlation coefficients are efficient to describe quantitatively the performance in preserving polarimetric information for PolSAR speckle filters. View full abstract»

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  • Inverse Profiling via an Effective Linearized Scattering Model and MRF Regularization

    Publication Year: 2011 , Page(s): 1021 - 1025
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (493 KB) |  | HTML iconHTML  

    The aim of this letter is to show how a joint adoption of a suitable regularization scheme and a proper rewriting of the traditional electromagnetic scattering equation allows introducing an interesting linear inversion tool which allows achieving nice reconstructions in many cases of practical interest. In particular, an innovative inversion approach which takes definite advantage from the joint use of the Contrast Source-Extended Born model and a Markov-random-field-based regularization scheme is proposed. Numerical examples, confirming accuracy usefulness, are reported and discussed. View full abstract»

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  • Interferometric Circular SAR Method for Three-Dimensional Imaging

    Publication Year: 2011 , Page(s): 1026 - 1030
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (704 KB) |  | HTML iconHTML  

    The aperture of 360° gives circular synthetic aperture radar (SAR) (CSAR) the capability to detect hidden target when its orientation is unknown. Subwavelength resolution can also be achieved when the target in the spotted area is observed under a complete circular aperture. Furthermore, the aspect angle diversity inherent to the circular trajectory makes possible a 3-D target reconstruction. However, the latter two potentials require certain target reflectivity homogeneity. For a highly directive scatterer, it has no resolving ability in the direction normal to the data collection plane. In this letter, a new interferometric CSAR method is presented to enhance the tomographic imaging capability for highly directive scatterers without sacrificing other scatterers' resolutions. This method takes advantage of the coherence and the phase difference between a pair of 3-D SAR images formed from data collected at two separate circular apertures to eliminate targets that focused at a wrong elevation. In addition, it uses two different transmit frequencies to solve the problem of phase cycle ambiguities. Finally, simulation results validate this new approach. View full abstract»

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  • Inexpensive FM-CW Radar for Boundary-Layer Precipitation Studies

    Publication Year: 2011 , Page(s): 1031 - 1035
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (824 KB) |  | HTML iconHTML  

    A vertically pointing C-band (5.8-GHz) frequency-modulated (FM) continuous-wave Doppler radar was developed for less than U.S. $6000, which can estimate the Doppler velocity power spectra from 20 to 300 m above the ground with a 5-m resolution. Three key design elements kept the costs low. First, the data acquisition system (DAS) commanded a direct digital synthesizer to start the FM sweep and then collected all voltage samples. This architecture insured phase coherence between the transmit FM sweep and the sampled voltages, which is critical for the Doppler processing that detects target phase changes over several successive FM sweeps. Second, a 5-m range resolution was achieved by increasing the FM bandwidth to over 36 MHz and decreasing the DAS sample rate to 500 kHz, enabling the use of an inexpensive DAS. Third, the Doppler processing at each range was achieved using two fast Fourier transforms (FFTs), i.e., a range FFT converted FM sweep voltages into in-phase and quadrature voltages I and Q at each range, and a Doppler FFT converted I and Q voltages from consecutive sweeps into the Doppler velocity power spectra. Observations show precipitation variability at 1-s and 5-m resolutions in the lowest 300 m of the atmosphere. View full abstract»

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  • Sliding Spotlight and TOPS SAR Data Processing Without Subaperture

    Publication Year: 2011 , Page(s): 1036 - 1040
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (571 KB) |  | HTML iconHTML  

    During the data acquisition of a sliding spotlight or terrain observation by progressive scan (TOPS) synthetic aperture radar (SAR), the steering of the antenna main beam increases the azimuth bandwidth but could result in the azimuth signal aliasing in the Doppler domain. To remove the aliasing, one has used a subaperture method. In this letter, we show a focusing scheme without the use of the subaperture for both sliding spotlight and TOPS SARs. In doing so, we eliminated the obvious increase in data volume or the subaperture division by choosing the pulse repetition frequency that is only 20% greater than the instantaneous bandwidth. The method was incorporated with an available imaging algorithm and then used to process simulated and collected data of the sliding spotlight and TOPS SARs. Well-focused results without aliasing were obtained. View full abstract»

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  • Application of Gaussian Mixture Model and Estimator to Radar-Based Weather Parameter Estimations

    Publication Year: 2011 , Page(s): 1041 - 1045
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (629 KB) |  | HTML iconHTML  

    The estimation of weather parameters such as attenuation and rainfall rates from remotely sensed weather radar data has been based mainly on deterministic regression models. This letter introduces a new Gaussian mixture parameter estimator (GMPE)-based framework to incorporate prior knowledge into this process. The GMPE makes possible a versatile model for parameter estimation under all conditions without compromising accuracy. Observations from dual-polarized and dual-frequency radar sensors can be utilized in the GMPE in a very flexible manner. Simulation examples have demonstrated that the GMPE has better estimation error performance than traditional methods for parameter estimation applications, particularly for noisy observations. The impacts of mixture number and state vector selections in the GMPE are also discussed. View full abstract»

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  • Optimal Parameter Estimation in Heterogeneous Clutter for High-Resolution Polarimetric SAR Data

    Publication Year: 2011 , Page(s): 1046 - 1050
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (834 KB) |  | HTML iconHTML  

    This letter presents a new estimation scheme for optimally deriving clutter parameters with high-resolution polarimetric synthetic aperture radar (POLSAR) data. The heterogeneous clutter in POLSAR data is described by the spherically invariant random vector model. Three parameters are introduced for the high-resolution POLSAR data clutter: the span, the normalized texture, and the speckle normalized covariance matrix. The asymptotic distribution of the novel span estimator is investigated. A novel heterogeneity test for the POLSAR clutter is also discussed. The proposed method is tested with airborne POLSAR images provided by the Office National d'Études et de Recherches Aerospatiales Radar Aéroporté Multi-spectral d'Etude des Signatures system. View full abstract»

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  • Impact of Gypsum on Electromagnetic Properties of Desert Soils

    Publication Year: 2011 , Page(s): 1051 - 1054
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (210 KB) |  | HTML iconHTML  

    Radar remote sensing of soil requires an understanding about the electromagnetic properties of soils. Propagation velocities and attenuation rates at ground-penetrating radar frequencies (0.25-4 GHz) were measured as a function of soil moisture content for soils from Iraq and Afghanistan. Soil samples in the study include two with and two without gypsum (CaSO4·2H2O) as a major mineral component. When measured at 100°C, volumetric moisture content of gypsum-rich soils ranged from 12% to 24%. In addition to the high moisture content, the propagation velocities were higher than expected, and attenuation rates were lower than expected for soils with moisture contents in this high range. The apparently anomalous relationship between high moisture content and low attenuation rate is explained by the presence and characteristics of gypsum in the soil. Radar signals are not affected by the chemically bound water molecules in gypsum which dehydrates at 100°C. These results show that soil mineralogy is critically important to the interpretation of dielectric properties. View full abstract»

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  • An Automated Approach to Detect Oceanic Eddies From Satellite Remotely Sensed Sea Surface Temperature Data

    Publication Year: 2011 , Page(s): 1055 - 1059
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (978 KB) |  | HTML iconHTML  

    Cyclonic (anticyclonic) oceanic eddies drive local upwelling (downwelling), leaving footprints in the sea surface temperature (SST) field as local extremes. Satellite-measured SST images can therefore be used to obtain information of the characteristics of oceanic eddies. Remotely sensed measurements represent very large data sets, both spatially and temporally. Manual eddy detection and analysis are thus practically impossible. In this letter, an automated scheme for eddy detection from remote sensing SST data is presented. The method is based on the analysis of velocity fields derived from SST measurements (thermal-wind velocity field). Using the geometric features of the velocity field, we can identify positions of eddy centers and derive eddy size, intensity, path, and lifetime. The scheme is applied to a realistic remotely sensed SST data set in a strong eddy activity region: Kuroshio Extension region. View full abstract»

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  • Support-Vector-Based Hyperspectral Anomaly Detection Using Optimized Kernel Parameters

    Publication Year: 2011 , Page(s): 1060 - 1064
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (414 KB) |  | HTML iconHTML  

    In this letter, a method to optimally determine the kernel bandwidth of the Gaussian radial basis function (RBF) kernel for support vector (SV)-based hyperspectral anomaly detection is presented. In this method, the support of a local background distribution is first nonparametrically learned by a technique called SV data description (SVDD). The SVDD optimally models an enclosing hypersphere around the local background data in a high-dimensional feature space associated with the Gaussian RBF kernel. Any test pixel that lies outside this hypersphere surrounding the local background is considered an anomaly and, hence, a possible target pixel. Considerable improvement in detection performance due to kernel parameter optimization can be seen in the simulation results when the algorithm is applied to hyperspectral images. View full abstract»

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  • Bayesian Hyperanalytic Denoising of SONAR Images

    Publication Year: 2011 , Page(s): 1065 - 1069
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (253 KB) |  | HTML iconHTML  

    The SOund Navigation And Ranging (SONAR) images are perturbed by speckle noise. This paper presents a new denoising method in the wavelet domain, which tends to reduce the speckle, preserving the structural features and the textural information of the scene. Shift invariance associated with good directional selectivity is important for the use of a wavelet transform (WT) in denoising of SONAR images. In this paper, we propose the use of a variant of hyperanalytic WT, which is quasi-shift invariant and has good directional selectivity in association with a maximum a posteriori filter named bishrink. This filter makes a very good treatment of the contours. The corresponding denoising algorithm is simple and fast. Its performance was proved on images perturbed by synthesized speckle noise and on real SONAR images. View full abstract»

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  • InSAR Tropospheric Stratification Delays: Correction Using a Small Baseline Approach

    Publication Year: 2011 , Page(s): 1070 - 1074
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB) |  | HTML iconHTML  

    Interferometric synthetic aperture radar (SAR) (InSAR) phase is affected by atmospheric path delay. It is common to separate the path delay into one component related to turbulent mixing processes and one component related to tropospheric stratification. Tropospheric stratification introduces phase delays correlating with topography, limiting interpretation of InSAR data in areas with steep topography. Improved access to SAR time series has led to the development of several innovative multitemporal InSAR algorithms. Small baseline (SB) is one such time-series method, based on combining and inverting a set of unwrapped interferograms to estimate surface displacement. In this letter, we present a method for estimating and correcting the effects of tropospheric stratification observed in an SB stack of interferograms. We demonstrate the value of this approach using InSAR data from the Envisat spacecraft and compare the InSAR estimated delays with results from a Global Positioning System network. View full abstract»

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  • Mesoscale Terrestrial Laser Scanning of Fluvial Gravel Surfaces

    Publication Year: 2011 , Page(s): 1075 - 1079
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (778 KB) |  | HTML iconHTML  

    Terrestrial laser scanning (TLS) point cloud data were gathered in the field of exposed gravel surfaces for sampling sites with a spatial extent of 6m × 6m. We propose in this letter a novel two-stage mean-based filter scheme for processing the point cloud to generate the digital surface model (DSM) at a resolution of 1 cm. To the authors' knowledge, this letter reports the first work of generating a DSM of a gravel surface of such a large spatial extent with high spatial resolution using TLS. The elevation variations attributed to gravel clasts and single grains can both be captured in the point cloud data. To eliminate data voids due to the obstruction of the line of sight, a multiple-scan strategy is employed, which includes four scans at the corners of the sampling site and two supplementary scans for the central 2m × 2m area. The resultant DSM exhibits good agreement with elevation profiles obtained using a traditional manual profiler. The proposed method is an effective tool for obtaining a quality DSM of fluvial gravel surfaces using TLS with fewer scans than previous study. View full abstract»

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  • Estimating Soil Moisture With the Support Vector Regression Technique

    Publication Year: 2011 , Page(s): 1080 - 1084
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (294 KB) |  | HTML iconHTML  

    This letter presents an experimental analysis of the application of the ε-insensitive support vector regression (SVR) technique to soil moisture content estimation from remotely sensed data at field/basin scale. SVR has attractive properties, such as ease of use, good intrinsic generalization capability, and robustness to noise in the training data, which make it a valid candidate as an alternative to more traditional neural-network-based techniques usually adopted in soil moisture content estimation. Its effectiveness in this application is assessed by using field measurements and considering various combinations of the input features (i.e., different active and/or passive microwave measurements acquired using various sensor frequencies, polarizations, and acquisition geometries). The performance of the SVR method (in terms of estimation accuracy, generalization capability, computational complexity, and ease of use) is compared with that achieved using a multilayer perceptron neural network, which is considered as a benchmark in the addressed application. This analysis provides useful indications for building soil moisture estimation processors for upcoming satellites or near-real-time applications. View full abstract»

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  • A Novel Strategy of Nonnegative-Matrix-Factorization-Based Polarimetric Ship Detection

    Publication Year: 2011 , Page(s): 1085 - 1089
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB) |  | HTML iconHTML  

    In this letter, a new strategy based on nonnegative matrix factorization (NMF) is proposed for polarimetric ship detection. This method utilizes the sparse feature of nonnegative eigenvalues, and the sparse degree is proposed to be estimated from the histogram which can reveal the sparse distribution of eigenvalues. Combining the nonnegative and sparse features, the NMF-based ship detection method can be implemented flexibly and efficiently. It has been carried out on the C-band quad polarimetric synthetic aperture radar (PolSAR) and dual PolSAR ocean data sets to validate its effectiveness. Unlike a constant-false-alarm-rate detector, the NMF method does not depend on target size and therefore offers improved detection performance under low-signal-to-clutter-ratio conditions. View full abstract»

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  • Four-Component Decomposition of Polarimetric SAR Images With Deorientation

    Publication Year: 2011 , Page(s): 1090 - 1094
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1359 KB) |  | HTML iconHTML  

    A modified Yamaguchi decomposition with deorientation is proposed for analyzing multilook polarimetric synthetic aperture radar (PolSAR) data. Deorientation is first applied to a coherence matrix; then, the coherence matrix is decomposed into four components by the Yamaguchi decomposition. A special kind of target is found for which the original Yamaguchi decomposition output is not appropriate. This problem is solved by applying deorientation prior to the Yamaguchi decomposition. Moreover, the deorientation procedure enhances double-bounce scattering from urban areas in the decomposition output. Comparisons of the Yamaguchi decompositions with and without deorientation are shown for PolSAR data from both airborne and spaceborne systems. View full abstract»

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  • Coherent Shift Estimation for Stacks of SAR Images

    Publication Year: 2011 , Page(s): 1095 - 1099
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (103 KB) |  | HTML iconHTML  

    Speckle tracking is used with synthetic aperture radar (SAR) images to estimate displacements, in ways that support or integrate interferometric measurements. This letter derives Fisher information expressions for the displacement estimation using coherent speckle tracking, for the multi-image scenario with an arbitrary coherence structure. Previous results were limited to image pairs. An estimator that approaches the theoretical bound is also proposed, establishing a link with phase estimation for multi-image SAR interferometry. The derivation of the Fisher information is given in the general case when the coherence is a function of the frequency. View full abstract»

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  • High-Resolution SAR Radargrammetry: A First Application With COSMO-SkyMed SpotLight Imagery

    Publication Year: 2011 , Page(s): 1100 - 1104
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (374 KB) |  | HTML iconHTML  

    The availability of new high-resolution radar spaceborne sensors offers new interesting potentialities for the acquisition of data useful for the generation of Digital Surface Models (DSMs). Two different approaches may be used to generate DSMs from Synthetic Aperture Radar (SAR) data: the interferometric and the radargrammetric one. At present, the importance of the radargrammetric approach is rapidly growing due to the new high-resolution imagery [up to 1 m Ground Sample Distance (GSD)] which can be acquired by COSMO-SkyMed, TerraSAR-X and RADARSAT-2 in SpotLight mode. The defined and implemented model is related to COSMO- SkyMed SpotLight imagery in zero-Doppler geometry; it performs a 3-D orientation based on two range and two zero-Doppler equations, allowing for the least squares estimation of some calibration parameters, related to satellite position and velocity and to the range measure. The model has been implemented in SISAR (Software per Immagini Satellitari ad Alta Risoluzione), a scientific software developed at the Geodesy and Geomatic Institute of the University of Rome “La Sapienza”. Starting from this model, based on a geometric reconstruction, also a tool for the Rational Polynomial Coefficients (RPCs) generations has been implemented. To test the effectiveness of the new model, a stereo pair over the test sites of Merano (Northern Italy) has been orientated using the rigorous model and the RPCs one, and first results of radargrammetric DSM generation are presented; they display the possibility to reach an overall average accuracy of 3.5 m. View full abstract»

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  • Internal Calibration for Stepped-Frequency Chirp SAR Imaging

    Publication Year: 2011 , Page(s): 1105 - 1109
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (567 KB) |  | HTML iconHTML  

    For synthetic aperture radar imaging, stepped-frequency chirp signals are widely used to obtain high range resolution. One advantage of the approach is the reduction of the instantaneous bandwidth and sampling rate requirements of the radar system. To reconstruct the spectrum of a wideband signal, the amplitude and phase discontinuity between contiguous pulses should be removed. Otherwise, the discontinuity will defocus the range profile and degrade the range resolution. In this letter, a detailed internal calibration technique combined with stepped-frequency mode is proposed to eliminate the discontinuity and thus improve the focusing quality of the final image. The simulation and real raw data experiments are performed to validate the proposed method. View full abstract»

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  • A New Method to Change Illumination Effect Reduction Based on Spectral Angle Constraint for Hyperspectral Image Unmixing

    Publication Year: 2011 , Page(s): 1110 - 1114
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (435 KB) |  | HTML iconHTML  

    Within the framework of the unmixing of hyperspectral images, the pixel mixture is a difficult problem to solve. This difficulty comes from several outliers which seriously affect the reliability of spectral unmixing results. The illumination change effect, where the image does not reflect the true appearance of the scene, in many cases due to shadow facts, is considered to be one of the most important outliers. The present work proposes a new approach called Spectral Angle Measure-based Spectral Unmixing which uses the spectral angle constraint for abundance quantification. The major benefit of this approach is its ability to take advantage of the geometric properties of the Spectral Angle Measure technique to estimate abundance quantification independently of the amplitude (magnitude) of the Endmembers spectral signatures, using only spectral angle measures. As a consequence, a significant reduction in spectral unmixed error corresponding to the spectral similarity within-class confusion is obtained. A second benefit concerns physical constraints which are respected. The experiment was conducted using simulated and real images to validate our approach and to compare it with a well known statistical one. View full abstract»

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  • Cramer–Rao Lower Bound Analysis of Vegetation Height Estimation With Random Volume Over Ground Model and Polarimetric SAR Interferometry

    Publication Year: 2011 , Page(s): 1115 - 1119
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB) |  | HTML iconHTML  

    The random volume over ground model, which is based on a simple description of the electromagnetic wave interaction with a vegetated media, allows one to define techniques to estimate the vegetation height from the polarimetric interferometric synthetic aperture radar observations. We discuss this issue with the Cramer-Rao lower bound (CRLB) which provides a minimal bound of the variance independently of the estimation if it is unbiased. The usefulness of this approach is illustrated on three different examples. The first example deals with the influence of a priori knowledge of some physical parameters. We show that reducing the number of unknown physical parameters does not necessarily improve the CRLB. The second example focus on the efficiency of the Cloude et al. height estimator. On the considered data, this estimator reaches the CRLB when the standard deviation equals approximately one meter. In the third example we optimize the radar baseline. View full abstract»

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Aims & Scope

IEEE Geoscience and Remote Sensing Letters (GRSL) is a monthly publication for short papers (maximum length 5 pages) addressing new ideas and formative concepts in remote sensing as well as important new and timely results and concepts.

 

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Meet Our Editors

Editor-in-Chief
Alejandro C. Frery
Universidade Federal de Alagoas