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Geoscience and Remote Sensing, IEEE Transactions on

Issue 6 • Date June 2008

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Displaying Results 1 - 25 of 36
  • [Front cover]

    Page(s): C1
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    Freely Available from IEEE
  • IEEE Transactions on Geoscience and Remote Sensing publication information

    Page(s): C2
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    Freely Available from IEEE
  • Table of contents

    Page(s): 1577 - 1578
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    Freely Available from IEEE
  • Some Aspects of Improving the Frequency Scaling Algorithm for Dechirped SAR Data Processing

    Page(s): 1579 - 1588
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (553 KB) |  | HTML iconHTML  

    The frequency scaling algorithm (FSA) was proposed to process the synthetic aperture radar (SAR) data acquired via the dechirp-on-receive approach. Some aspects of improving the FSA are investigated in this paper, based on which an extended FSA (EFSA) is presented. The general purpose of the EFSA is to reduce the effect of range spectrum shift of the intermediate processing results, which occurs during the scaling operation in the FSA, so as to achieve a more effective utilization of the processed bandwidth. The EFSA is implemented through time shifting the scaling and the inverse scaling functions used in the FSA and also the adjustment of the scaling factor. The derivation of the EFSA is detailed in this paper. Point target simulation in squinted imaging geometry indicates that the presented algorithm is more suitable for large-squint applications. View full abstract»

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  • Refocusing Through Building Walls Using Synthetic Aperture Radar

    Page(s): 1589 - 1599
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (909 KB) |  | HTML iconHTML  

    Through-wall imaging/sensing using a synthetic aperture array technique is studied by employing ultrawideband antennas and for wide incidence angles. The propagation through building walls, such as brick and poured concrete in response to point sources near the walls, is simulated by using high-frequency methods. Reciprocity is used to find the responses of point targets behind walls, which are then used to simulate the synthetic aperture radar (SAR) imaging through the walls. The effect of building walls on the target-image distortions is investigated by simulations and measurements. It is shown that by using the idea of match filtering, the effect of the wall can be compensated for, and the point target response can be reconstructed, provided that the wall parameters are known. An optimization method based on minimization of squared error in the SAR image domain within an area confined within the expected point-spread function is used to estimate the wall parameters and sharpen the image simultaneously. A controlled experiment within the laboratory environment is performed to verify the methods presented. It is shown that for an ultrawideband system operating over a frequency band of 1-3 GHz, highly distorted images of two point targets in close proximity of each other behind a wall can be resolved after refocusing. A dual-frequency synthetic method is also presented that can improve the cross-range resolution of the refocused image. View full abstract»

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  • An Error Prediction Framework for Interferometric SAR Data

    Page(s): 1600 - 1613
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2054 KB) |  | HTML iconHTML  

    Three of the major error sources in interferometric synthetic aperture radar measurements of terrain elevation and displacement are baseline errors, atmospheric path length errors, and phase unwrapping errors. In many processing schemes, these errors are calibrated out by using ground control points (GCPs) (or an external digital elevation model). In this paper, a simple framework for the prediction of error standard deviation is outlined and investigated. Inputs are GCP position, a priori GCP accuracy, baseline calibration method along with a closed-form model for the covariance of atmospheric path length disturbances, and a model for phase unwrapping errors. The procedure can be implemented as a stand-alone add-on to standard interferometric processors. It is validated by using a set of single-frame interferograms acquired over Rome, Italy, and a double difference data set over Flevoland, The Netherlands. View full abstract»

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  • Analysis of Ground-Based SAR Data With Diverse Temporal Baselines

    Page(s): 1614 - 1623
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1252 KB) |  | HTML iconHTML  

    In this paper, the algorithms developed for satellite synthetic aperture radar (SAR) interferometry were adapted to the ground-based SAR (GB-SAR) configuration and used for detecting the displacements of an alpine landslide which have occurred over many years. Indeed GB-SAR interferometry is based on the same principles as satellite SAR techniques but benefits from the GB-SAR's versatility and capability of gathering many images per day. In monitoring applications of landslides moving only few centimeters per year, as the case here reported, the GB-SAR sensor is installed at repeated intervals several months apart over the observation period. Although the revisiting time is very similar to the satellite one, for each survey, lasting two or three days, more than ten images are available. They are analyzed separately and in combination with images from other surveys for coherent pixel selection. Interferograms are formed by cross-combining images from different surveys. Finally, the evolution of the deformation across the surveys is retrieved in a least square sense without any assumptions on its regularity. The used GB-SAR technique is described in detail in this paper, and the results obtained with regard to a landslide in the Italian Alps that has been monitored over a period of about three years are discussed. View full abstract»

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  • Traffic Surveillance System Based on a High-Resolution Radar

    Page(s): 1624 - 1633
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1149 KB) |  | HTML iconHTML  

    Traffic surveillance is an important civilian application of radars. The current high-resolution radars give new opportunities so that the traffic application may be redefined. In this paper, a traffic scenario with a high-resolution radar is presented. A range-bin alignment method, the Global Range Alignment, which comes from the focusing techniques in inverse synthetic aperture radar, is applied to obtain further capabilities than the usual velocity measurement: distinction between vehicle types via length estimation and adequate management in situations with simultaneous targets. Preliminary results from a real scenario using a high-resolution linear frequency-modulated continuous-wave millimeter-wave radar are shown. View full abstract»

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  • Scattering From Layered Structures With One Rough Interface: A Unified Formulation of Perturbative Solutions

    Page(s): 1634 - 1643
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (559 KB) |  | HTML iconHTML  

    In this paper, we investigate analytically the connection between the existing first-order small perturbation method solutions for the scattering from a layered structure with one rough interface. First of all, by using effectively the concept of generalized reflection coefficients, we cast the existing models in a unified more compact formulation and point out the connection between the different analytical solutions. The obtained reformulations of the available analytical solutions allow us to subsequently prove the consistency of the considered models. Finally, a suitable expansion is performed that leads us to understand the physical meaning of the analytical expressions. The obtained unified formulation also opens the way toward a general closed-form solution for the problem of scattering by a layered structure with an arbitrary number of corrugated interfaces. View full abstract»

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  • How Does Multiple Scattering Affect the Spaceborne W-Band Radar Measurements at Ranges Close to and Crossing the Sea-Surface Range?

    Page(s): 1644 - 1651
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1495 KB) |  | HTML iconHTML  

    A radar simulator capable of treating multiple-breakscattering effects has been upgraded to include the interaction with a Kirchoff surface, which realistically reproduces the effect of water surfaces. Multiple-scattering effects explain in a straightforward way some peculiar features of the first images delivered by the 94-GHz cloud-profiling radar onboard the CloudSat, overpassing precipitating systems. The reflectivity profiles without the usual peaks at surface range are found to be distinctive signatures of strong multiple scattering. Moreover, multiple scattering is responsible for producing long signal tails at apparent ranges far below the surface with a strong sensitivity on the microphysical assumptions of the icy segment of the cloud. The estimates of multiple-scattering enhancement at surface and close to the surface range and the saturation levels for simplified precipitating profiles for both CloudSat and EarthCARE configurations are provided. View full abstract»

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  • An Efficient FDTD Method for Axially Symmetric LWD Environments

    Page(s): 1652 - 1656
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (923 KB) |  | HTML iconHTML  

    In this paper, an unconditionally stable finite- difference time-domain (FDTD) method in cylindrical coordinates is developed to analyze electromagnetic responses under axially symmetric measure-while-drilling/logging-while-drilling (MWD/LWD) environments. The method is based on the application of the Crank-Nicholson scheme to the FDTD method in cylindrical coordinates. To accelerate the solution of this approach, an algebraic multigrid method is applied. For several MWD/LWD electromagnetic simulations, it is observed that the proposed method can be close to 20 times faster than the conventional FDTD method. View full abstract»

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  • Physical Optics Curved-Boundary Dielectric Plate Scattering Formulas for an Accurate and Efficient Electromagnetic Characterization of a Class of Natural Targets

    Page(s): 1657 - 1666
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (821 KB) |  | HTML iconHTML  

    Closed-form representations of the physical optics (PO) field scattered in the far zone by plane penetrable dielectric angular sectors of arbitrary opening angle featuring a conical-section boundary are derived in terms of incomplete cylindrical functions (ICFs). The proposed expressions, possibly in combination with PO formulas for the scattering from polygonal plates, allow one to evaluate the scattering from flat dielectric plates with both convex and concave curved edges in a very efficient manner and constitute a useful tool to improve the accuracy of the geometrical characterization of a class of natural scatterers. In order to check the correctness and computational effectiveness of the proposed scattered-field solutions, comparisons with results obtained by accurate completely numerical PO calculations are provided. Simulation data by the method of moments are also presented to assess the applicability of the PO approximation to the considered sample scattering geometries. View full abstract»

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  • POLSAR Image Analysis of Wetlands Using a Modified Four-Component Scattering Power Decomposition

    Page(s): 1667 - 1673
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (959 KB) |  | HTML iconHTML  

    It is important to monitor environmental changes of the Earth's cover by remotely sensed data. This paper analyzes seasonal changes of a wetland by a modified polarimetric four-component scattering power decomposition method. The data sets analyzed here are L- and X-band fully polarimetric synthetic aperture radar (POLSAR) data, which have been acquired by the NICT/JAXA airborne polarimetric and interferometric synthetic aperture radar system in 2004. Since there existed a deficiency in the currently adopted decomposition schemes in that negative powers appear in a few pixels in the image analysis, we modified the approach taking into account physical conditions. It is shown by the modified scheme that the seasonal changes and features of the vegetation near Sakata Lagoon in Niigata, Japan, are observed clearly, demonstrating the utility of POLSAR image analysis for wetland assessments in general. View full abstract»

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  • Effect of Salinity on the Dielectric Properties of Geological Materials: Implication for Soil Moisture Detection by Means of Radar Remote Sensing

    Page(s): 1674 - 1688
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2026 KB) |  | HTML iconHTML  

    We consider the exploitation of dielectric properties of saline deposits for the detection and mapping of moisture in arid regions on both Earth and Mars. We present simulated and experimental study in order to assess the effect of salinity on the complex permittivity of geological materials and, therefore, on the radar backscattering coefficient in the [1-7 GHz] frequency range. Laboratory measurements are performed on sand/sodium chloride aqueous mixtures using a vectorial network analyzer coupled to an open-ended coaxial dielectric probe. We aim at calibrating and validating semiempirical dielectric mixing models. In particular, we evaluated the dependence of the real and imaginary parts of complex permittivity on the microwave frequency, water content, and salinity. Our results confirm that if the real part is mainly affected by the moisture content, the imaginary part is more sensitive to salinity. In addition to the classic formulas of mixing models, the ionic-conductivity losses, which are due to mobile ions in the saline solution, are taken into account in order to better assess the effect of salinity on the dielectric properties of mixtures. Dielectric mixing models are then used as input parameters for the simulation of the radar backscattering coefficients by means of an analytical model: the integral equation model. Simulation results show that salinity should have a significant impact on the radar backscattering recorded in synthetic aperture radar data in terms of the magnitude of the backscattering coefficient. Moreover, our results suggest that VV polarization provides a greater sensitivity to salinity than HH polarization. View full abstract»

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  • An Artificial-Neural-Network-Based Integrated Regional Model for Rain Retrieval Over Land and Ocean

    Page(s): 1689 - 1696
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (769 KB) |  | HTML iconHTML  

    An integrated regional model is proposed for rain-rate retrievals over land/ocean from the brightness temperature (Tb) values of the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). The polarization-corrected temperature calculated from the 85.5-GHz channels is also considered as one of the inputs along with the nine channel Tb values. This model is applicable over the region between and . For this purpose, an artificial neural network is utilized. The collocated precipitation radar (PR) near-surface rain rates as given by a 2A25 data product is considered as a target value. The methodology consists of the separation of land and ocean pixels, the separation of stratiform and convective pixels over land/ocean, and the selection of important features (inputs) for the multilayer perceptron network by the feature selection technique for each group. For the separation of land/ocean pixels, the Tb values of the 10.65-GHz vertical channel are utilized. The values are utilized to separate the stratiform and convective pixels both over land and ocean. The rain retrieval from the developed model is validated with TRMM PR. Overall result shows the better agreement of the model-retrieved rain rate with the PR observation compared to the TMI (2A12) rain rate particularly over land. The rain retrieved from the developed model is further validated with Doppler weather radar. A reasonably good agreement is observed between these two estimations. View full abstract»

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  • Characteristics of TRMM/PR System Noise and Their Application to the Rain Detection Algorithm

    Page(s): 1697 - 1704
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1610 KB) |  | HTML iconHTML  

    This study investigates the characteristics of system noise sampled by the Precipitation Radar (PR) onboard the Tropical Rainfall Measuring Mission satellite. First, we examine the long-term trend in system noise. The result shows that the system noise level was quite stable for a long time period except for a few sudden change events. The averaged system noise shows a periodic change that relates to the temperature of the PR. This change corresponds to the changes in the solar beta angle, and the amplitude of the fluctuation is about 0.15 dB. The contribution of surface emission from the ocean to the system noise is also examined by averaging the system noise data under a no-rain condition over a long period (e.g., one month) to remove the effect of the temperature fluctuation related to the solar beta angle. The resulting amplitude is less than 0.1 dB, and the spatial distribution almost corresponds to the pattern of the sea surface temperature. These results confirm that the system noise of the PR is quite stable, indicating that the fluctuation of the sampled system noise is caused mainly by the fading effect. The characteristics of the system noise of three rain categories - ldquorain certain,rdquo ldquorain possible,rdquo and ldquono-rainrdquo - are examined by taking a histogram. Because the PRpsilas system noise is supposed to be stable, broadening the system noise level of about 2.5 dB almost corresponds to the fading effect. The histograms of rain-certain and of no-rain show a similar shape with a difference of a few tenths of decibels. The higher noise levels in rain-certain conditions are caused by the emission from raindrops. In contrast, the rain-possible histogram shows a widespread and skewed shape. It can be explained by saying that the rain-possible pixels are obtained when the sampled noise level is made accidentally small by the fading effect. Therefore, a fixed noise level threshold is introduced to the rain/no-rain classification for a more rel- - iable rain-possible classification. The result shows that the rain area increases by about 15%, and the amount of rainfall increases by about 1% by adding reliable rain-possible pixels to the current standard product. View full abstract»

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  • Spatial and Temporal Varying Thresholds for Cloud Detection in GOES Imagery

    Page(s): 1705 - 1717
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1579 KB) |  | HTML iconHTML  

    A new cloud detection technique has been developed and applied to GOES-12 Imager data. The bispectral composite threshold (BCT) technique uses only the 11- and 3.9- channels, and composite imagery generated from these channels, in a four-step cloud detection procedure to produce a binary cloud mask at single-pixel resolution. An innovative aspect of this algorithm is the use of 20-day composites of the 11- and the 11-3.9- channel difference imagery to represent spatially and temporally varying clear-sky thresholds for the bispectral cloud tests. The BCT cloud detection technique has been validated against a ldquotruthrdquo data set generated by the manual determination of the sky conditions from available satellite imagery for four seasons during 2003-2004. The day-and-night algorithm has been shown to determine the correct sky conditions 87.6% of the time (on average) over the eastern two-thirds of the U.S. and surroundings oceans. The incorrectly determined conditions arose from missing clouds 8.9% of the time or from overdetermining clouds 3.5% of the time. Nearly 82% of the misses came in the presence of low clouds. Only small variations in algorithm performance occurred between day-night, land-ocean, and between seasons. The algorithm performed best in the warmer seasons (90.9% correct during the summer versus 81.8% correct in the winter season) and during the day, when the solar illumination provides enhanced surface atmospheric cloud contrast in the infrared channels, and least well during the winter season. The algorithm was found to slightly underdetermine clouds at night and during times of low sun angle and tends to be cloud conservative during the day, particularly in the summertime. View full abstract»

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  • The GLOBCARBON Cloud Detection System for the Along-Track Scanning Radiometer (ATSR) Sensor Series

    Page(s): 1718 - 1727
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1809 KB) |  | HTML iconHTML  

    The GLOBCARBON initiative aims to develop a service to generate fully calibrated estimates of at-land products using, in combination, data from the Along-Track Scanning Radiometer (ATSR) sensor series, MERIS and VEGETATION. A fundamental requirement of such processing is the effective removal of extraneous effects introduced by cloud, cloud shadow, snow, and atmosphere in these data. This paper reports on the implementation and extension of a new cloud and snow processing system for land, which is for the ATSR sensor series. The snow processor is as implemented for the Moderate Resolution Imaging Spectrometer, whereas the cloud processor is based on APOLLO, with extensions to generate the probabilities of cloud presence and a further test to eliminate the cloud missed by APOLLO. The system was tested on 48 images representing a wide range of cloud types and forms over three contrasting biomes-boreal forest, desert savannah, and tropical evergreen forest. Excellent results are produced and represent a major improvement over the original flagging system. The approach has been adopted in GLOBCARBON for the processing of 500 000 ATSR scenes and 20 000 AATSR striplines. View full abstract»

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  • Sample Bias Estimation for Cloud-Free Aerosol Effects Over Global Oceans

    Page(s): 1728 - 1732
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (591 KB) |  | HTML iconHTML  

    Satellite-based methods for estimating the top-of-atmosphere shortwave direct radiative effect (SWRE) either use the spatial distribution of aerosol optical thickness (AOT) coupled with radiative transfer calculations or combine the AOT with broadband radiative energy data sets such as the Clouds and the Earth's Radiant Energy System (CERES). The first approach typically utilizes the AOT at a spatial resolution of from the Moderate Resolution Imaging Spectroradiometer (MODIS), and the second method relies on the same AOT, but it is convolved within the CERES footprint and has spatial resolutions that are greater than . Therefore, the SWRE may vary as a result of this difference in spatial resolution that we call sample bias. We correct for this sample bias using the AOT reported at the MODIS and the CERES product levels coupled with the radiative efficiency (SWRE per-unit optical depth) for 13 regions over the ocean as a function of season between December 2003 and November 2004 and demonstrate that the sample biases are seasonally and spatially dependent. Overall, nearly 75% of the pixels over the global oceans require a sample bias adjustment of some form. However, the adjustment is large , which is less than 7% of the time, primarily during the spring and summer months, in association with large dust aerosol concentrations with large optical depth gradients. If sample biases are not accounted for, they will globally reduce the SWRE by an average of 30% (4.1 versus ), although regionally, the adjustment could be larger (). We argue that these bias corrections are robust and simpler to use when compared with methods that employ narrow- to broadband relationships. View full abstract»

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  • A Hybrid Reconstruction Algorithm for 3-D Ionospheric Tomography

    Page(s): 1733 - 1739
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (583 KB) |  | HTML iconHTML  

    In this paper, a hybrid reconstruction algorithm (HRA) is presented to solve the ill-posed inverse problem associated with 3-D ionospheric stochastic tomography. In this new method, the ionospheric electron density (IED) can be inverted by using two steps. First, a truncated singular value decomposition (TSVD) method, whose value is independent on any initial estimation, is used to resolve the ill-posed problem of the tomography system. Second, taking into account the "approximation" of its solution, an iterative improvement process of the solution is then implemented by utilizing the conventional algebraic reconstruction algorithm (ART). The HRA, therefore, offers a more reasonable approach to choose an initial approximate for the ART and to improve the quality of the final reconstructed image. A simulated experiment demonstrates that the HRA method is superior to the TSVD or the ART alone for the tomographic inversion of IED. Finally, the HRA is used to perform GPS-based tomographic reconstruction of the IED at mid- and low-latitude regions. View full abstract»

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  • McCART: Monte Carlo Code for Atmospheric Radiative Transfer

    Page(s): 1740 - 1752
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (726 KB) |  | HTML iconHTML  

    McCART is a numerical procedure to solve the radiative transfer equation for light propagation through the atmosphere from visible to near-infrared wavelengths. The procedure has been developed to study the effect of the atmosphere in the remote sensing of the Earth, using aerospace imaging spectrometers. The simulation is run for a reference layered plane nonabsorbing atmosphere and a plane ground with uniform reflectance. For a given distribution of ground reflectance and for a specific profile of scattering and absorption properties of the atmosphere, the spectral response of the sensor is obtained in a short time from the results of the Monte Carlo simulation by using scaling relationships and symmetry properties. The procedure also includes an accurate analysis of the adjacency and trapping effects due to multiple scattering of photons coming from neighboring pixels. McCART can generate synthetic images of the Earth's surface for arbitrary viewing conditions. The results can be used to establish the limits of applicability of approximate algorithms for the processing and analysis of hyperspectral images acquired by imaging spectrometers. In addition, the algorithm can be used to develop procedures for atmospheric correction for the accurate retrieval of the spectral ground reflectance. View full abstract»

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  • Quantifying Uncertainty in Modeling Snow Microwave Radiance for a Mountain Snowpack at the Point-Scale, Including Stratigraphic Effects

    Page(s): 1753 - 1767
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1346 KB) |  | HTML iconHTML  

    Merging microwave radiances and modeled estimates of snowpack states in a data assimilation scheme is a potential method for snowpack characterization. A radiance assimilation scheme for snow requires a land surface model (LSM) coupled to a radiative transfer model (RTM). In this paper, we explore the degree of model fidelity required in order for radiance assimilation to yield benefits for snowpack characterization. Specifically, we characterize the uncertainty of Microwave Emission Model for Layered Snowpacks (MEMLS) radiance predictions by quantifying model accuracy and sensitivity to the following: (1) the LSM snowpack layering scheme and (2) the properties of the snow layers, including melt-refreeze ice layers. MEMLS was consistent with the measured brightness temperatures at 18.7 and 36.5 GHz with a bias (mean absolute error) of 0.1 K (3.1 K) for the vertical polarization and 3.4 K (9.3 K) for the horizontal polarization. An error in the predictions at horizontal polarization is due to uncertainty in ice-layer properties. It was found that in order for predicted brightness temperatures from the coupled LSM and RTM to be adequate for radiance assimilation purposes, the following must be satisfied: (1) the LSM snowpack layering scheme must accurately represent the stratigraphic snowpack layers; (2) dynamics of melt-refreeze ice layers must be modeled explicitly, and the predicted density of melt-refreeze layers must be accurate within ; and (3) the MEMLS correlation length must be predicted within 0.016 mm, or effective optical grain diameter must be predicted within 0.045 mm. Recommendations for future field measurements are made. View full abstract»

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  • Brightness Temperature Reconstruction Using BGI

    Page(s): 1768 - 1773
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (531 KB) |  | HTML iconHTML  

    This paper departs from the popular usage of the Backus-Gilbert inversion (BGI) method as a tool for inversion of antenna temperature measurements in microwave radiometry. The BGI method is applied in this paper to enhance the information content of an existing set of oversampled brightness-temperature (TB) data. The purpose is to isolate the inversion process from its resolution enhancement counterpart. The advantage gained is that the resolution enhancement can be performed in a simplified way and in a different level of processing that starts with the scan-mode TB data product and simply requires with it the knowledge of the antenna gain pattern and the sensor's scan geometry. The technique is demonstrated with the 19.35-GHz Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) channel, which provides oversampled TB data. The radiometric resemblance of this channel with that of the 37 GHz and geocollocation of their TB footprints facilitate validation of the enhancement of features. The significance of oversampling the low-frequency (LF) radiometer channels is underscored in the process, which gives the authors the confidence to propose oversampling of the LF data for the forthcoming sensor Microwave Analysis and Detection of Rain and Atmospheric Structures (MADRAS) onboard the Megha_Tropiques mission, which is a joint ISRO-CNES collaboration (due for launch in 2009). View full abstract»

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  • Quantitative Mineral Assessment of Apatite, Calcite/Dolomite, and Phlogopite Powder Mixtures by Using VSWIR Reflectance

    Page(s): 1774 - 1782
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (339 KB) |  | HTML iconHTML  

    Quantitative assessment of mineral powders made from mono/two-mineral blocks sampled from the Siilinjarvi apatite ore deposit is the target of this paper. The blocks were composed of apatite, calcite/dolomite, and phlogopite. The blocks were powdered and mixed into a set of 21 well-documented mixtures. Their visible to short-wave infrared (VSWIR) reflectance spectra were recorded by using the FieldSpecFR Spectrometer. Linear unconstrained unmixing of the spectra resulted in highly biased estimates in spite of the fact that the mean absolute residual error of the unmixing was very small. The bias, which is actually induced by camouflage between mineral classes, could approximately be removed by a polynomial function. This resulted in unbiased estimates for apatite calcite/dolomite and phlogopite. Best results were obtained when the wavelengths were limited to the SWIR area only. This two-part procedure consisting of the linear unmixing and the camouflage correction gives one more aspect to subpixel classification. Training data are given not only for the classes but also for their interaction. In this paper, the mean absolute residual error of the estimated volumetric fractions of apatite, calcite/dolomite, and phlogopite from the spectra was 1.32%, which is smaller than the result in the previous VSWIR studies concerning the assessment of mineral powders. This reflectance method offers a very quick tool for several mineral-related applications. View full abstract»

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  • Validation of the Surface Air Temperature Products Retrieved From the Atmospheric Infrared Sounder Over China

    Page(s): 1783 - 1789
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (724 KB) |  | HTML iconHTML  

    The Atmospheric Infrared Sounder (AIRS) is the first of a new generation of high spectral resolution atmospheric sounders, which are expected to obtain atmospheric temperature and water vapor profiles with high accuracy. We are interested in investigating the validation of AIRS surface air temperature retrievals, particularly in the region of China. The surface air temperature observations obtained from 540 ground meteorological stations over China were collected, and quantitative comparisons were performed between the AIRS Version 4 retrievals and the ground observations. Then, the main causes of retrieval errors are discussed in detail. Results show that the rms errors of the AIRS surface air temperature retrievals are correlated with the terrain altitudes of the meteorological stations. With the altitude increasing, the rms errors have a trend of gradual increase. The rms errors are insensitive to the ground-observed cloud fraction. With the observed cloud fraction increasing, the small-scale oscillations of rms errors occur. In mountainous and desert regions, the rms errors are larger and can reach up to 11 K sometimes. Furthermore, the AIRS surface air temperature retrievals have better performance in January than in July. In central and eastern China, even the accuracy of accepted quality products in January approaches the goal of the AIRS Team. 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.

 

Full Aims & Scope

Meet Our Editors

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