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  • Artikel  (440)
  • 2010-2014  (440)
  • 2012  (440)
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  • Artikel  (440)
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  • 2010-2014  (440)
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  • 1
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    FFT-Accelerated Analysis of Scattering From Complex Dielectrics Embedded in Uniaxial Layered Media (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
    Details
    Publikationsdatum: 2012-12-20
    Beschreibung: An efficient integral-equation method is presented for the analysis of electromagnetic scattering from arbitrarily shaped 3-D dielectric objects embedded in a single layer of a uniaxial planar-layered medium. The proposed method employs a mixed-potential volume electric-field integral equation (VEFIE) that permits the object of interest to be dispersive, anisotropic, inhomogeneous, and of arbitrary shape. The VEFIE is solved by an iterative frequency-domain method-of-moments procedure. The object is discretized by tetrahedral elements, and the procedure is accelerated by the adaptive integral method, which reduces the computational costs by enclosing the tetrahedral mesh with an auxiliary regular grid and performing anterpolation (mesh to grid), propagation (grid to grid), interpolation (grid to mesh), and near-zone correction (mesh to mesh) steps. The computationally dominant propagation step of the method is accelerated by decomposing the Green's functions into convolution and correlation terms in the stratification direction and using 3-D fast Fourier transforms to multiply the resulting propagation matrices with the necessary vectors. If the object of interest is meshed using $N$ tetrahedra that are of a single length scale, then the setup time, memory requirement, and the iterative matrix-solution time (per iteration) of the proposed method scale as $O(N)$ , $O(N)$ , and $O(Nlog N)$ , respectively. Numerical results validate the method's accuracy and efficiency for various problems relevant to geophysical exploration.
    Print ISSN: 1545-598X
    Digitale ISSN: 1558-0571
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie , Geologie und Paläontologie
    Publiziert von Institute of Electrical and Electronics Engineers (IEEE)
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
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    Registration of Optical and SAR Satellite Images by Exploring the Spatial Relationship of the Improved SIFT (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publikationsdatum: 2012-12-20
    Beschreibung: Although feature-based methods have been successfully developed in the past decades for the registration of optical images, the registration of optical and synthetic aperture radar (SAR) images is still a challenging problem in remote sensing. In this letter, an improved version of the scale-invariant feature transform is first proposed to obtain initial matching features from optical and SAR images. Then, the initial matching features are refined by exploring their spatial relationship. The refined feature matches are finally used for estimating registration parameters. Experimental results have shown the effectiveness of the proposed method.
    Print ISSN: 1545-598X
    Digitale ISSN: 1558-0571
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie , Geologie und Paläontologie
    Publiziert von Institute of Electrical and Electronics Engineers (IEEE)
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
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    Azimuth Overlapped Subaperture Algorithm in Frequency Domain for Highly Squinted Synthetic Aperture Radar (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
    Details
    Publikationsdatum: 2012-12-20
    Beschreibung: The high-resolution imaging of a highly squinted synthetic aperture radar remains difficult because of the severe coupling between the range and the azimuth. “Squint minimization” compensates for the range walking in the azimuth time domain, which efficiently increases the orthogonality between the range and the azimuth. However, this “squint minimization” introduces the azimuth space-variant phases, which can be compensated by the azimuth nonlinear chirp-scaling (ANCS) algorithm using large computational loads. In this letter, an azimuth overlapped subaperture algorithm (AOSA) is proposed to compensate for these phases in the Doppler frequency domain. The validity constraint of this algorithm is then analyzed. The AOSA has an advantage over ANCS in terms of the computational load and is considerably more suitable for real-time processing.
    Print ISSN: 1545-598X
    Digitale ISSN: 1558-0571
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie , Geologie und Paläontologie
    Publiziert von Institute of Electrical and Electronics Engineers (IEEE)
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 4
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    Wavelet Packet Analysis and Gray Model for Feature Extraction of Hyperspectral Data (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
    Details
    Publikationsdatum: 2012-12-20
    Beschreibung: Wavelet packet analysis (WPA) and gray model (GM) are investigated for nonlinear unsupervised feature extraction of hyperspectral remote sensing data in this letter. Treated as derivative series, a hyperspectral response curve of each pixel is decomposed into an approximation and various detailed compositions by WPA, and then, GM is continuously applied to find the relationship among those detailed compositions. Cluster–space representation is used for determining the optimal wavelet. New extracted features can reveal the intrinsic identities of hyperspectral data. Experimental results show the feasibility and reliability of our proposed method in terms of classification accuracy.
    Print ISSN: 1545-598X
    Digitale ISSN: 1558-0571
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie , Geologie und Paläontologie
    Publiziert von Institute of Electrical and Electronics Engineers (IEEE)
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 5
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    RFI Mitigation Using Two-Scale Estimators for Statistical Variance (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
    Details
    Publikationsdatum: 2012-12-20
    Beschreibung: The well-known sample variance estimator utilizes $N$ samples from a random process to first estimate the process mean. The estimator then uses the same $N$ samples to estimate variance from this mean. Process variance could also be estimated by first using less than $N$ samples to estimate the mean, followed by using all $N$ samples to estimate variance. Two-scale estimators of this type, both causal and noncausal, are defined. Statistics for these estimators are derived, which are valid for samples from any statistical distribution. These statistics are used to improve analysis of a previously reported device called the double detector. In microwave radiometry, the double detector senses the presence of deterministic signals, often called radio-frequency interference, that corrupt the usual measurement consisting only of Planck radiation.
    Print ISSN: 1545-598X
    Digitale ISSN: 1558-0571
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie , Geologie und Paläontologie
    Publiziert von Institute of Electrical and Electronics Engineers (IEEE)
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 6
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    Seasonal Snow Cover Mapping in Alpine Areas Through Time Series of COSMO-SkyMed Images (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publikationsdatum: 2012-12-20
    Beschreibung: A time series of COSMO-SkyMed (CSK) images is exploited for detection of seasonal snow cover in alpine areas. For the first time, a complete time series of CSK images acquired during snow fall and melt periods in winter 2010–2011 is addressed to verify the snow cover mapping capabilities of X-band radar images under different conditions (from dry to wet snow). The algorithm for snow detection is based on a multitemporal approach with the concept that free water in the snowpack attenuates the X-band synthetic aperture radar signal and wet snow can be classified by comparing images acquired under wet snow and snow-free conditions. Thresholds to make this distinction are compared across all the images to check sensitivity to different winter conditions and land-use classes. The impact of variable and fixed thresholds on the retrieved snow-covered areas is assessed. Snow maps from CSK images compared with Landsat Enhanced Thematic Mapper Plus snow maps indicate a constant underestimation in the detection of snow extent, particularly during winter season, thus showing a scarce sensitivity of X-band signals to snow in dry conditions. Probability of error maps are also calculated for each CSK snow map, thus providing information on the classification error associated to each pixel labeled as snow. The analysis of the snow line variation during spring determines good time consistency in the determination of snow maps from CSK images.
    Print ISSN: 1545-598X
    Digitale ISSN: 1558-0571
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie , Geologie und Paläontologie
    Publiziert von Institute of Electrical and Electronics Engineers (IEEE)
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 7
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    Development and Demonstration of an Artificial Immune Algorithm for Mangrove Mapping Using Landsat TM (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publikationsdatum: 2012-12-20
    Beschreibung: Mangroves are valuable contributors to coastal ecosystems; knowledge of the dynamics of mangrove ecosystems is important in the context of global change. To obtain this knowledge, remote sensing is an indispensable means, yet it poses challenges since the accuracy is sometimes unsatisfactory in distinguishing mangroves from other land cover types with traditional classification methods. In this letter, we proposed a modified artificial immune algorithm (AIA), in which the antibodies represent the candidate solutions and the antigens are expressed by the fitness function. Multiclass coevolution was combined with the concept of clonal selection to ensure computation of an optimal clustering center in parallel for each land cover type. A cluster-center-oriented decimal encoding method for antibodies was adopted, and the inner class variance and the between-class difference together were used to formulate the fitness function. Furthermore, a design of the antibody solubility-based selection operator and nonuniform mutation operator was undertaken. Applying this modified AIA to a Landsat Thematic Mapper multispectral remote sensing imagery in the Zhangjiang estuary in southeastern China, we found that the AIA substantially improved classification accuracy over traditional methods, showing an overall accuracy of 90% $(hbox{kappa coefficient} = 0.88)$ and was capable to discern mangrove well (commission of 10% and omission of 22%).
    Print ISSN: 1545-598X
    Digitale ISSN: 1558-0571
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie , Geologie und Paläontologie
    Publiziert von Institute of Electrical and Electronics Engineers (IEEE)
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 8
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    An Improved SAC Algorithm Based on the Range-Keystone Transform for Doppler Rate Estimation (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
    Details
    Publikationsdatum: 2012-12-20
    Beschreibung: Doppler rate is an important parameter in synthetic aperture radar (SAR) signal processing since it affects the SAR image focusing. There are many approaches to estimate the Doppler rate from SAR data; however, some approaches are not appropriate for spotlight SAR, which is focused with the two-step algorithm, since, after azimuth preprocessing, the signal is aliased in the azimuth time domain. Although the shift-and-correlation (SAC) algorithm may be suitable for such signals, it is proposed for the stripmap imaging mode; and when it is used to estimate the Doppler rate for spotlight SAR, some problems, such as the high computational load from zero padding and the constraint of the focus depth, may occur. In this letter, an improved Doppler rate estimation approach, which is called the Keystone–SAC algorithm, is proposed. An iterative scheme is presented to estimate the ambiguity number, and a special case when the ambiguity number splits into two numbers is analyzed. The real spotlight SAR data processing results are used to validate the effectiveness of the proposed algorithm.
    Print ISSN: 1545-598X
    Digitale ISSN: 1558-0571
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie , Geologie und Paläontologie
    Publiziert von Institute of Electrical and Electronics Engineers (IEEE)
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 9
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    Initial Validation of SMOS Vegetation Optical Thickness in Iowa (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
    Details
    Publikationsdatum: 2012-12-20
    Beschreibung: The European Space Agency's Soil Moisture and Ocean Salinity (SMOS) satellite mission provides microwave L-band measurements of vegetation optical thickness over the Earth. Optical thickness is related to water held in vegetation. The water content of crops varies over the growing season from a minimum during planting to a maximum during reproduction and back to a minimum during senescence. We found that in Iowa in 2010 the change in SMOS optical thickness over the growing season can be related to crop yields. However, there are inconsistencies in the optical thickness data, particularly high-frequency variation and unexpected changes outside of the growing season. We hypothesize that the unexpected changes during the dormant periods are due to changes in soil surface roughness caused by land management activities and show a relationship between changes in roughness and changes in optical thickness, which may be confusing the SMOS retrieval algorithm.
    Print ISSN: 1545-598X
    Digitale ISSN: 1558-0571
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie , Geologie und Paläontologie
    Publiziert von Institute of Electrical and Electronics Engineers (IEEE)
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 10
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    Side-Lobe Cancelation in DInSAR Pixel Selection With SVA (2012)
    Institute of Electrical and Electronics Engineers (IEEE)
    Details
    Publikationsdatum: 2012-12-20
    Beschreibung: Synthetic aperture radar (SAR) systems are inherently band limited in both range and azimuth, and hence, the point spread function (PSF) has the shape of a bidimensional sinc function. In addition, all SAR images are slightly oversampled, and as a consequence, the contribution of a single target extends to more than a single cell. The main lobe and the side lobes of strong scatterers are sometimes clearly visible in the images. This characteristic of the SAR images must be considered when applying differential interferometric synthetic aperture radar (DInSAR) pixel selection algorithms. For persistent scatterers, the properties, for instance, the amplitude stability, are preserved in both redundant information around the main lobe and side lobes. For this reason, a cluster of pixels rather than just the pixel position corresponding to the exact location of the target will be detected. Spatially variant apodization (SVA) is a nonlinear filter based on cosine-on-pedestal weighting functions able to achieve a total side-lobe cancelation without degrading the original image resolution. When working with complex data under complex scattering scenarios, the PSF moves away from the ideal bidimensional sinc, and the SVA performance worsens. The amplitude and phase of the original images could be distorted by the SVA filtering compromising the pixel selection and the quality of the final DInSAR results. In this letter, SVA is used to method locate in the image the side lobes of high-power scatterers and generate a mask while preserving the amplitude and phase of the original images.
    Print ISSN: 1545-598X
    Digitale ISSN: 1558-0571
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie , Geologie und Paläontologie
    Publiziert von Institute of Electrical and Electronics Engineers (IEEE)
    Standort Signatur Einschränkungen Verfügbarkeit
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