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Geoscience and Remote Sensing, IEEE Transactions on

Issue 2 • Date Feb. 2005

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Displaying Results 1 - 25 of 28
  • [Front cover]

    Publication Year: 2005 , Page(s): c1
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  • IEEE Transactions on Geoscience and Remote Sensing publication information

    Publication Year: 2005 , Page(s): c2
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  • Table of contents

    Publication Year: 2005 , Page(s): 205 - 206
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  • Tree height influence on ERS interferometric phase in boreal forest

    Publication Year: 2005 , Page(s): 207 - 217
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1024 KB) |  | HTML iconHTML  

    The European Remote Sensing 1/2 (ERS-1/2) "tandem" coherence has been shown to provide estimates of stem volume in boreal forest in agreement with in situ data. Tree height estimation from ERS interferometric phase represents a further step in the investigations concerning the retrieval of biophysical parameters using repeat-pass synthetic aperture radar (SAR) interferometry. At two test sites located in Sweden and Finland, sets of respectively nine and eight ERS "tandem" interferograms were available. Images acquired under stable winter weather conditions and during nighttime were found to be less affected by atmospheric artifacts. Reduction of atmospheric artifacts in interferograms was performed with a phase screen estimated over a dense grid of open areas. Nonetheless, at each test site, only a limited set of pairs was useful for tree height investigations. Under stable winter conditions, the interferometric tree height obtained from an inversion of the differential interferometric phase at stand level was found to be much lower than the true tree height. Spread and uncertainty in the interferometric tree height measurements were caused by phase noise and residual atmospheric artifacts. Using the semiempirical interferometric water cloud model (IWCM), the modeled interferometric tree height was generally in reasonable agreement with the measurements, showing the need of a phase term in interferometric modeling of forests. The inversion of the IWCM for tree height retrieval showed the strong effect of phase noise and atmospheric artifacts on the estimates. Hence, tree height retrieval from ERS repeat-pass SAR interferometry seems to have limited forestry applications. The results also indicate under what conditions the forest influence is small on digital elevation models derived from repeat-pass interferometry. View full abstract»

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  • Comparison of regularized inversion methods in synthetic aperture imaging radiometry

    Publication Year: 2005 , Page(s): 218 - 224
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (544 KB) |  | HTML iconHTML  

    This paper is concerned with the reconstruction of radiometric brightness temperature maps from interferometric measurements. The corresponding inverse problem is often ill-posed unless a regularizing constraint is introduced in order to provide a unique and stable solution. Standard regularizing approaches are compared and illustrated with numerical simulations carried out in reference to the Soil Moisture and Ocean Salinity space mission led by the European Space Agency. View full abstract»

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  • Observation and characterization of radar backscatter over Greenland

    Publication Year: 2005 , Page(s): 225 - 237
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2520 KB) |  | HTML iconHTML  

    Characterization of the microwave signature of the Greenland snow surface enables delineation of the different snow facies and is a tool for tracking the effects of climate change. A new empirical observation model is introduced that uses a limited number of parameters to characterize the snow surface based on the dependence of radar backscatter on incidence angle, azimuth angle, spatial gradient, and temporal rate of change. The individual model parameters are discussed in depth with examples using data from the NASA Scatterometer (NSCAT) and from the C-band European Remote Sensing (ERS) satellite Advanced Microwave Instrument in scatterometer mode. The contribution of each model term to the overall accuracy of the model is evaluated. The relative contributions of the modeled dependencies vary by region. Two studies illustrating applications of the model are included. First, interannual changes over the Greenland ice sheet are investigated using nine years of ERS data. Surface changes are observed as anomalies in the σ° model parameters. Second, intraannual variations of the surface are investigated. These changes are observed in the average backscatter normalized to a given observation geometry. The results indicate that the model can be used to obtain a more complete understanding of multiyear change and to obtain low-variance high temporal resolution observations of intraannual changes. The model may be applied for increased accuracy in scatterometer, synthetic aperture radar (SAR), and wide-angle SAR studies. View full abstract»

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  • Microwave backscatter modeling of erg surfaces in the Sahara desert

    Publication Year: 2005 , Page(s): 238 - 247
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (824 KB) |  | HTML iconHTML  

    The Sahara desert includes large expanses of sand dunes called ergs. These dunes are formed and constantly reshaped by prevailing winds. Previous study shows that Saharan ergs exhibit significant radar backscatter (σ°) modulation with azimuth angle (f). We use σ° measurements observed at various incidence angles and f from the NASA Scatterometer (NSCAT), the SeaWinds scatterometer, the ERS scatterometer (ESCAT), and the Tropical Rainfall Measuring Mission's Precipitation Radar to model the σ° response from sand dunes. Observations reveal a characteristic relationship between the backscatter modulation and the dune type, i.e., the number and orientation of the dune slopes. Sand dunes are modeled as a composite of tilted rough facets, which are characterized by a probability distribution of tilt with a mean value, and small ripples on the facet surface. The small ripples are modeled as cosinusoidal surface waves that contribute to the return signal at Bragg angles only. Longitudinal and transverse dunes are modeled with rough facets having Gaussian tilt distributions. The model results in a σ° response similar to NSCAT and ESCAT observations over areas of known dune types in the Sahara. The response is high at look angles equal to the mean tilts of the rough facets and is lower elsewhere. This analysis provides a unique insight into scattering by large-scale sand bedforms. View full abstract»

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  • Seismic source model for moving vehicles

    Publication Year: 2005 , Page(s): 248 - 256
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (912 KB) |  | HTML iconHTML  

    We develop a method for the loading of ground by moving vehicles in large finite-difference time-domain simulations of seismic wave propagation. The objective is to realistically produce two distinct types of ground loading for either wheeled or tracked vehicles in our propagation models: lower frequency loading associated with suspension dynamics and higher frequency impulsive loading associated with tire treads or wheels rolling over individual track blocks. These loading characteristics are important because field measurements show that vehicle ground forcing in both frequency bands produces seismic surface waves that networked sensors can remotely process for security applications. The method utilizes a vehicle-dynamics model to calculate a response to vehicle acceleration and ground features such as bumps; calculates forces transmitted to the ground; distributes these forces to staggered points of a finite-difference model; and simulates seismic wave propagation away from the vehicle. We demonstrate the method using bounce-and-pitch models of wheeled and tracked vehicles. We show that by carefully preprocessing force inputs, we can accurately simulate wave propagation and seismic signatures in finite-difference analyses of vehicles moving continuously over terrain. View full abstract»

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  • Three-dimensional simulation of eccentric LWD tool response in boreholes through dipping formations

    Publication Year: 2005 , Page(s): 257 - 268
    Cited by:  Papers (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1184 KB) |  | HTML iconHTML  

    We simulate the response of logging-while-drilling (LWD) tools in complex thee-dimensional (3-D) borehole environments using a finite-difference time-domain (FDTD) scheme in cylindrical coordinates. Several techniques are applied to the FDTD algorithm to improve the computational efficiency and the modeling accuracy of more arbitrary geometries/media in well-logging problems: (1) a 3-D FDTD cylindrical grid to avoid staircasing discretization errors in the transmitter, receiver, and mandrel geometries; (2) an anisotropic-medium (unsplit) perfectly matched layer (PML) absorbing boundary condition in cylindrical coordinates is applied to the FDTD algorithm, leading to more compact grids and reduced memory requirements; (3) a simple and efficient algorithm is employed to extract frequency-domain data (phase and amplitude) from early-time FDTD data; (4) permittivity scaling is applied to overcome the Courant limit of FDTD and allow faster simulations of lower frequency tool; and (5) two locally conformal FDTD (LC-FDTD) techniques are applied to better simulate the response of logging tools in eccentric boreholes. We validate the FDTD results against the numerical mode matching method for problems where the latter is applicable, and against pseudoanalytical results for eccentric borehole problems. The comparisons show very good agreement. Results from 3-D borehole problems involving eccentric tools and dipping beds simultaneously are also included to demonstrate the robustness of the method. View full abstract»

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  • Fast solution of mixed-potential time-domain integral equations for half-space environments

    Publication Year: 2005 , Page(s): 269 - 279
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (816 KB) |  | HTML iconHTML  

    A fast Fourier transform-accelerated integral-equation based algorithm to efficiently analyze transient scattering from planar perfect electrically conducting objects residing above or inside a potentially lossy dielectric half-space is presented. The algorithm requires O(NtNs(logNs+log2Nt)) CPU and O(NtNs) memory resources when analyzing electromagnetic wave interactions with uniformly meshed planar structures. Here, Nt and Ns are the numbers of simulation time steps and spatial unknowns, respectively. The proposed scheme is therefore far more efficient than classical time-marching solvers, the CPU and memory requirements of which scale as O(Nt2Ns2) and O(NtNs2). In the proposed scheme, all pertinent time-domain half-space Green functions are (pre) computed from their frequency-domain counterparts via inverse discrete Fourier transformation. In this process, in-band aliasing is avoided through the application of a smooth and interpolatory window. Numerical results demonstrate the accuracy and efficiency of the proposed algorithm. View full abstract»

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  • Two-dimensional scattering of a Gaussian beam by a periodic array of circular cylinders

    Publication Year: 2005 , Page(s): 280 - 285
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1160 KB) |  | HTML iconHTML  

    The two-dimensional scattering of a Gaussian beam by a periodic array of circular cylinders is studied. The incident Gaussian beam is expressed as a superposition of plane waves of different amplitudes and different incident angles, using the plane-wave spectrum technique based on Fourier optics. For each plane wave, the scattered field is calculated with the T-matrix of an isolated circular cylinder and its lattice sums characterizing a periodic arrangement of the circular cylinders. The circular cylinders may be perfect conductors, dielectric or gyrotropic cylinders, as long as their T-matrices are known. View full abstract»

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  • Low-grazing-angle microwave scattering from a three-dimensional spilling breaker crest: a numerical investigation

    Publication Year: 2005 , Page(s): 286 - 294
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB) |  | HTML iconHTML  

    The microwave backscattering from a three-dimensional (3-D) target approximating the rough crest of a gently spilling water wave at low grazing angle illumination has been numerically examined. The target surfaces were synthesized from the direct two-dimensional (2-D) measurement of the time evolution of the upwave-downwave cross-section of a wave-tank breaker. The reference scattering was found using the multilevel fast multipole algorithm implemented with impedance boundary conditions and resistive surface loading to suppress nonphysical edge diffraction. The scattering was compared with the predictions of the two-scale model and a synthesis of the 3-D backscattering from individual 2-D calculations. Specular reflection from a bulge feature that appeared on the crest prior to breaking dominated the backscattering at both polarizations, overwhelming even the strong vertical polarization Bragg scattering that appeared in the corresponding scattering from the individual 2-D profiles used to synthesize the 3-D target. The scattering from the surface including the bulge could be accurately modeled using a coherent addition of the scattering from the 2-D profiles. The two-scale model performed poorly whenever there are steep sections on the surface that provide significant quasi-specular back-reflection. Accuracy improved when the specular points were eliminated and the dominant scattering roughness was fully illuminated, but was still sensitive to the surface-roughness scale-separation threshold used in its application. View full abstract»

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  • Estimating the soil dielectric constant via scattering measurements along the specular direction

    Publication Year: 2005 , Page(s): 295 - 305
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB) |  | HTML iconHTML  

    We propose a soil dielectric constant retrieval scheme based on the use of the ratio of power densities scattered at HH and VV polarizations along the specular direction for different incidence angles and/or frequencies. The method relies on the minimum squares technique and is based on the observation that at variance with the backscattering case, in the specular case the small perturbation method (SPM) and the Kirchhoff approach both lead to the same expression of the copolarized ratio. Accordingly, it is expected that its evaluation is rather robust, to hold under a wide range of surface roughnesses. We present method-of-moments (MoM) simulations that confirm this expectation, and we test the validity of the overall retrieval scheme, as well as its sensitivity to measurement errors (calibration errors and fading or speckle noise), by applying the algorithm to data simulated by using the MoM. Theoretical and practical problems related to the implementation of measurements along the specular direction are also discussed. The proposed method is amenable to the new generation of bistatic remote sensing instruments. View full abstract»

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  • A study of ocean-like surface thermal emission and reflection using Voronovich's small slope approximation

    Publication Year: 2005 , Page(s): 306 - 314
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB) |  | HTML iconHTML  

    Monte Carlo simulations are used to compute average direct surface thermal emission and reflected atmospheric radiation using the "active" small slope approximation of Voronovich. The surfaces considered are realizations of an ocean-like spectrum and contain features ranging from 64 to 0.5 electromagnetic wavelengths. The parallel computing approach of the study is described, and results are compared with predictions from the commonly applied "two-scale" theory of sea emission. Results show a reasonable level of agreement in a small height surface case, which degrades as the surface height is increased. View full abstract»

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  • The empirical formula for calculating the complex effective permittivity of an aqueous electrolyte solution at microwave frequency

    Publication Year: 2005 , Page(s): 315 - 320
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (528 KB) |  | HTML iconHTML  

    So far, some models have been established to calculate the complex effective permittivity of an aqueous electrolyte solution. Almost all of the models based on the fitting parameters in Debye's equation were used to calculate the complex effective permittivity of a few aqueous electrolyte solutions, such as saline water and seawater. In this paper, we propose a new empirical formula to calculate the complex effective permittivity of a mixed aqueous electrolyte solution based on the measurement of complex impact factors for fundamental ions. The calculated complex effective permittivities of six mixed aqueous electrolyte solutions were compared with the measured results at 915 and 2450 MHz. The complex permittivity of saline water obtained by this model was compared with the published data as well. Good agreement can be observed. View full abstract»

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  • Ionospheric tomography using GNSS reflections

    Publication Year: 2005 , Page(s): 321 - 326
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (848 KB)  

    We report a preliminary analysis of the impact of Global Navigation Satellite System Reflections (GNSS-R) data on ionospheric monitoring over the oceans. The focus is on a single polar Low Earth Orbiter (LEO) mission exploiting GNSS-R as well as Navigation (GNSS-N) and Occultation (GNSS-O) total electron content (TEC) measurements. In order to assess impact of the data, we have simulated GNSS-R/O/N TEC data as would be measured from the LEO and from International Geodesic Service (IGS) ground stations, with an electron density (ED) field generated using a climatic ionospheric model. We have also developed a new tomographic approach inspired by the physics of the hydrogen atom and used it to effectively retrieve the ED field from the simulated TEC data near the orbital plane. The tomographic inversion results demonstrate the significant impact of GNSS-R: three-dimensional ionospheric ED fields are retrieved over the oceans quite accurately, even as, in the spirit of this initial study, the simulation and inversion approaches avoided intensive computation and sophisticated algorithmic elements (such as spatio-temporal smoothing). We conclude that GNSS-R data over the oceans can contribute significantly to a Global/GNSS Ionospheric Observation System (GIOS). View full abstract»

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  • A wavelet-based algorithm to estimate ocean wave group parameters from radar images

    Publication Year: 2005 , Page(s): 327 - 336
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2936 KB) |  | HTML iconHTML  

    In recent years, new remote sensing techniques have been developed to measure two-dimensional (2-D) sea surface elevation fields. The availability of these data has led to the necessity to extend the classical analysis methods for one-dimensional (1-D) buoy time series to two dimensions. This paper is concerned with the derivation of group parameters from 2-D sea surface elevation fields using a wavelet-based technique. Wave grouping is known to be an important factor in ship and offshore safety, as it plays a role in dangerous resonance phenomenons and the generation of extreme waves. Synthetic aperture radar (SAR) data are used for the analysis. The wavelet technique is introduced using synthetic ocean surfaces and simulated SAR data. It is shown that the group structure of the ocean wave field can be recovered from the SAR image if the nonlinear imaging effects are moderate. The method is applied to a global dataset of European Remote Sensing satellite (ERS-2) wave mode data. Different group parameters including the area covered by the largest group and the number of groups in a given area are calculated for over 33 000 SAR images. Global maps of the parameters are presented. For comparison, classical 1-D grouping parameters are calculated from colocated wave model data showing good overall agreement with the wavelet-derived parameters. ERS-2 image mode data are used to study wave fields in coastal areas. Waves approaching the island of Sylt in the North Sea are investigated, showing the potential of the wavelet technique to analyze the spatial wave dynamics associated with the bottom topography. Observations concerning changes of wavelength and group parameters are compared to linear wave theory. View full abstract»

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  • Remote bathymetry of the littoral zone from AVIRIS, LASH, and QuickBird imagery

    Publication Year: 2005 , Page(s): 337 - 347
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2304 KB) |  | HTML iconHTML  

    An efficient, physics-based remote bathymetry method for the littoral zone is described and illustrated with applications to QuickBird, Littoral Airborne Sensor: Hyperspectral (LASH), and Airborne Visible/Infrared Spectrometer (AVIRIS) spectral imagery. The method combines atmospheric correction, water reflectance spectral simulations, and a linear unmixing bathymetry algorithm that accounts for water surface reflections, thin clouds, and variable bottom brightness, and can incorporate blends of bottom materials. Results include depth maps, bottom color visualizations, and in favorable cases, approximate descriptions of the water composition. In addition, atmospheric correction was advanced through new capabilities added to the Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes (FLAASH) and Moderate Resolution Transmittance (MODTRAN) codes, including characterization of the aerosol wavelength dependence and a discrete-ordinate-method radiative transfer scaling technique for rapid calculation of multiply scattered radiance. View full abstract»

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  • Estimation and monitoring of bare soil/vegetation ratio with SPOT VEGETATION and HRVIR

    Publication Year: 2005 , Page(s): 348 - 354
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB) |  | HTML iconHTML  

    Covering soils with vegetation during the fallow and planting seasons is one of the main ways to reduce water pollution, by restricting pollutant fluxes to aquatic systems. The bare soil/vegetation ratio monitoring can be carried out daily with a coarse spatial resolution using SPOT VEGETATION (1 km). Nevertheless, land-cover changes detected at a regional scale with this ratio may be due to winter vegetation cover changes as well as the influence of climatic events. Therefore, observed changes have to be validated from a local-scale analysis with higher spatial resolution data. The aim of this study is to develop a technique that allows high or low variations detected at a regional scale to be assessed from SPOT VEGETATION images with data acquired at a higher scale, SPOT High Resolution Visible and Infrared images in our case. In this study, the link between the images from the two sensors is achieved from the design of an artificial neural network method based on a Kohonen self-organizing map. The originality of this method lies in the use of external knowledge from ground observations and the use of temporal behavior to solve such a change of scale. Results of testing this method by using a potential change map based on the last few years' land-cover observations have shown a good correspondence between the observed and predicted bare soil/vegetation balance with regards to the spatial resolution difference between the two sensors. View full abstract»

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  • Terra MODIS on-orbit spatial characterization and performance

    Publication Year: 2005 , Page(s): 355 - 365
    Cited by:  Papers (36)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1496 KB) |  | HTML iconHTML  

    The Moderate Resolution Imaging Spectroradiometer (MODIS) Proto-Flight Model, onboard the National Aeronautics and Space Administration's Earth Observing System Terra spacecraft, has been in operation for over four years. It has 36 spectral bands and a total of 490 detectors located on four focal plane assemblies (FPAs). MODIS makes observations at three spatial resolutions (nadir): 0.25 km (bands 1-2), 0.5 km (bands 3-7), and 1 km (bands 8-36). The instrument's spatial characterization was measured prelaunch using an integration and alignment collimator. Parameters measured included the detectors' instantaneous field-of-view (IFOV), band-to-band registration (BBR), and line spread function in both the along-scan and along-track directions. On-orbit, the spatial characterization is periodically measured using the onboard spectro-radiometric calibration assembly (SRCA). This paper describes the SRCA BBR algorithms, characterization methodologies, and on-orbit results. A Fourier approach used to calculate the along-track BBR is also described. This approach enhances the algorithm's robustness in comparison with the conventional centroid approach. On-orbit results show that the Terra MODIS focal planes shifted slightly during launch and initial on-orbit operation. Since then they have been very stable. The BBR is within 0.16 km (nadir IFOV) in the along-scan direction and 0.23 km (nadir IFOV) in the along-track direction among all bands. The small but noticeable periodic variation of the on-orbit BBR can be attributed to the annual cycling of instrument temperature due to Sun-Earth distance variation. The visible FPA position has the largest temperature dependence among all FPAs, 17 m/K along-scan and 0.6 m/K along-track. View full abstract»

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  • The impact of subsampling on MODIS level-3 statistics of cloud optical thickness and effective radius

    Publication Year: 2005 , Page(s): 366 - 373
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (680 KB) |  | HTML iconHTML  

    The Moderate Resolution Imaging Spectroradiometer (MODIS) Level-3 optical thickness and effective radius cloud product is a gridded 1°×1° dataset that is derived from aggregation and subsampling of every fifth pixel, along both spatial directions, of Level-2 orbital swath data (Level-2 granules). The present study examines the impact of this subsampling on the mean, standard deviation, and inhomogeneity parameter statistics of optical thickness and effective radius. The methodology is simple and consists of estimating mean errors for a large collection of Terra and Aqua Level-2 granules by taking the difference of the statistics at the original and subsampled resolutions. It is shown that the Level-3 subsampling does not affect the various quantities investigated to the same degree, with second-order moments suffering greater subsampling errors, as expected. Mean errors drop dramatically when averages over a sufficient number of regions (e.g., monthly and/or zonal averages) are taken, pointing to a dominance of errors that are of random nature. When histograms built from subsampled data with the same binning rules as in the Level-3 dataset are used to reconstruct the quantities of interest, the mean errors do not deteriorate significantly. The results in this paper provide guidance to users of MODIS Level-3 optical thickness and effective radius cloud products on the range of errors due to subsampling they should expect and perhaps account for, in scientific work with this dataset. In general, subsampling errors should not be a serious concern when moderate temporal (e.g., monthly) and/or spatial (e.g., zonal) averaging is performed. View full abstract»

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  • A cluster-based approach for detecting man-made objects and changes in imagery

    Publication Year: 2005 , Page(s): 374 - 387
    Cited by:  Papers (37)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3624 KB) |  | HTML iconHTML  

    A new unified approach to object and change detection is presented that involves clustering and analyzing the distribution of pixel values within clusters over one or more images. Cluster-based anomaly detection (CBAD) can detect man-made objects that are: (1) present in a single multiband image; (2) appear or disappear between two images acquired at different times; or (3) manifest themselves as spectral differences between two sets of bands acquired at the same time. Based on a Gaussian mixture model, CBAD offers an alternative to compute-intensive, sliding-window algorithms like Reed and Yu's RX-algorithm for single-image object detection. It assumes that background pixel values within clusters can be modeled as Gaussian distributions about mean values that vary cluster-to-cluster and that anomalies (man-made objects) have values that deviate significantly from the distribution of the cluster. This model is valid in situations where the frequency of occurrence of man-made objects is low compared to the background so that they do not form distinct clusters, but are instead split up among multiple background clusters. CBAD estimates background statistics over clusters, not sliding windows, and so can detect objects of any size or shape. This provides the flexibility of filtering detections at the object level. Examples show the ability to detect small compact objects such as vehicles as well as large, spatially extended features (e.g., built-up and bomb-damaged areas). Unlike previous approaches to change detection, which compare pixels, vectors, features, or objects, cluster-based change detection involves no direct comparison of images. In fact, it is identical to the object detection algorithm, different only in the way it is applied. Preliminary results show cluster-based change detection is less sensitive to image misregistration errors than global change detection. The same cluster-based algorithm can also be used for cross-spectral anomaly detection. An example showing the detection of thermal anomalies in Landsat Thematic Mapper imagery is provided. View full abstract»

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  • Kernel RX-algorithm: a nonlinear anomaly detector for hyperspectral imagery

    Publication Year: 2005 , Page(s): 388 - 397
    Cited by:  Papers (88)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1600 KB) |  | HTML iconHTML  

    We present a nonlinear version of the well-known anomaly detection method referred to as the RX-algorithm. Extending this algorithm to a feature space associated with the original input space via a certain nonlinear mapping function can provide a nonlinear version of the RX-algorithm. This nonlinear RX-algorithm, referred to as the kernel RX-algorithm, is basically intractable mainly due to the high dimensionality of the feature space produced by the nonlinear mapping function. However, in this paper it is shown that the kernel RX-algorithm can easily be implemented by kernelizing the RX-algorithm in the feature space in terms of kernels that implicitly compute dot products in the feature space. Improved performance of the kernel RX-algorithm over the conventional RX-algorithm is shown by testing several hyperspectral imagery for military target and mine detection. View full abstract»

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  • On the residual term in the linear mixture model and its dependence on the point spread function

    Publication Year: 2005 , Page(s): 398 - 401
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB) |  | HTML iconHTML  

    The linear mixture model has been extensively used in the analysis of satellite data, especially for characterization of surface cover at subpixel scales. In the model, a multispectral signal is assumed to comprise a weighted sum of characteristic spectra, the weights corresponding to fractional coverage. The residual is almost invariably assumed to be independent of the weights, and usually taken to arise from Gaussian noise; the maximum-likelihood estimate of the abundances is then found by minimizing a quadratic objective function. Nonuniform sampling of the radiance distribution within the field of view means, however, that there is some dependence of the residual on the true surface abundances, when it is understood that these are simple area averages. We account for this signal-dependent noise by incorporating the modified variance-covariance matrix of the residual into the quadratic objective function. It is shown that, despite the increased complexity of the new objective function, it is minimized by the traditional estimator. This is true whether or not we require the estimated abundances to sum to unity, i.e., whether the minimization is constrained or unconstrained. The constrained and unconstrained estimators are here treated together by deploying a "sum-to-one" parameter. View full abstract»

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  • Development of comprehensive accuracy assessment indexes for building footprint extraction

    Publication Year: 2005 , Page(s): 402 - 404
    Cited by:  Papers (9)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (72 KB) |  | HTML iconHTML  

    Presents a suite of indexes for comprehensively evaluating the results of automated building extraction. The indexes described include detection rate, correctness, matched overlay, area omission error, area commission error, root mean square error, corner difference, area difference, perimeter difference, and shape similarity. These proposed unbiased quality measures should enable the accuracy assessment of the building extraction process to address extraction issues such as completeness, geometric accuracy, and building shape similarity. View full abstract»

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Aims & Scope

 

IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING (TGRS) is a monthly publication that focuses on the theory, concepts, and techniques of science and engineering as applied to sensing the land, oceans, atmosphere, and space; and the processing, interpretation, and dissemination of this information.

 

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Meet Our Editors

Editor-in-Chief
Antonio J. Plaza
University of Extremadura