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Journal ArticleDOI

Emission of rough surfaces calculated by the integral equation method with comparison to three-dimensional moment method simulations

TL;DR: The results based on the new version (advanced IEM) indicate that significant improvements for emissivity prediction may be obtained for a wide range of roughness scales, in particular in the intermediate roughness regions.
Abstract: This paper presents a model of microwave emissions from rough surfaces. We derive a more complete expression of the single-scattering terms in the integral equation method (IEM) surface scattering model. The complementary components for the scattered fields are rederived, based on the removal of a simplifying assumption in the spectral representation of Green's function. In addition, new but compact expressions for the complementary field coefficients can be obtained after quite lengthy mathematical manipulations. Three-dimensional Monte Carlo simulations of surface emission from Gaussian rough surfaces were used to examine the validity of the model. The results based on the new version (advanced IEM) indicate that significant improvements for emissivity prediction may be obtained for a wide range of roughness scales, in particular in the intermediate roughness regions. It is also shown that the original IEM produces larger errors that lead to tens of Kelvins in brightness temperature, which are unacceptable for passive remote sensing.
Citations
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Journal ArticleDOI
TL;DR: In this article, a detailed description of soil and vegetation modelling in L-MEB is given in order to address these needs, and the use of LMEB in soil moisture retrievals is evaluated for several experimental data sets over agricultural crops.

604 citations

Journal ArticleDOI
TL;DR: In this paper, the authors provide a critical and up-to-date survey of the analytical approximate methods that are encountered in scattering from random rough surfaces and provide synthetic tables of their respective performances, according to a dozen important requirements a valuable method should meet.
Abstract: This review is intended to provide a critical and up-to-date survey of the analytical approximate methods that are encountered in scattering from random rough surfaces. The underlying principles of the different methods are evidenced and the functional form of the corresponding scattering amplitude or cross-section is given. The reader is referred to the original papers in order to obtain the explicit expressions of the coefficients and kernels. We have tried to identify the main strengths and weaknesses of the various theories. We provide synthetic tables of their respective performances, according to a dozen important requirements a valuable method should meet. Both scalar acoustic and vector electromagnetic theories are equally addressed.

413 citations


Cites background from "Emission of rough surfaces calculat..."

  • ...single-scattering contribution) as well as the general IEM expressions (including multiple-scattering terms) have been continuously amended until recently [136, 255, 256]....

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Journal ArticleDOI
TL;DR: A comprehensive review of the progress in remote sensing of soil moisture, with focus on technique approaches for soil moisture estimation from optical, thermal, passive microwave, and active microwave measurements is presented in this paper.
Abstract: Surface soil moisture is one of the crucial variables in hydrological processes, which influences the exchange of water and energy fluxes at the land surface/atmosphere interface. Accurate estimate of the spatial and temporal variations of soil moisture is critical for numerous environmental studies. Recent technological advances in satellite remote sensing have shown that soil moisture can be measured by a variety of remote sensing techniques, each with its own strengths and weaknesses. This paper presents a comprehensive review of the progress in remote sensing of soil moisture, with focus on technique approaches for soil moisture estimation from optical, thermal, passive microwave, and active microwave measurements. The physical principles and the status of current retrieval methods are summarized. Limitations existing in current soil moisture estimation algorithms and key issues that have to be addressed in the near future are also discussed.

390 citations

Journal ArticleDOI
TL;DR: The theoretical basis of LSE measurements is given, a description of the published methods, and the validation methods, which are of importance in verifying the uncertainty and accuracy of retrieved emissivity.
Abstract: As an intrinsic property of natural materials, land surface emissivity LSE is an important surface parameter and can be derived from the emitted radiance measured from space. Besides radiometric calibration and cloud detection, two main problems need to be resolved to obtain LSE values from space measurements. These problems are often referred to as land surface temperature LST and emissivity separation from radiance at ground level and as atmospheric corrections in the literature. To date, many LSE retrieval methods have been proposed with the same goal but different application conditions, advantages, and limitations. The aim of this article is to review these LSE retrieval methods and to provide technical assistance for estimating LSE from space. This article first gives a description of the theoretical basis of LSE measurements and then reviews the published methods. For clarity, we categorize these methods into 1 semi-empirical or theoretical methods, 2 multi-channel temperature emissivity separation TES methods, and 3 physically based methods PBMs. This article also discusses the validation methods, which are of importance in verifying the uncertainty and accuracy of retrieved emissivity. Finally, the prospects for further developments are given.

370 citations

Journal ArticleDOI
15 Jul 2008-Sensors
TL;DR: A literature review is made that summarizes the problems encountered when parameterizing soil roughness as well as the reported impact of the errors made on the retrieved soil moisture.
Abstract: Synthetic Aperture Radar has shown its large potential for retrieving soil moisture maps at regional scales. However, since the backscattered signal is determined by several surface characteristics, the retrieval of soil moisture is an ill-posed problem when using single configuration imagery. Unless accurate surface roughness parameter values are available, retrieving soil moisture from radar backscatter usually provides inaccurate estimates. The characterization of soil roughness is not fully understood, and a large range of roughness parameter values can be obtained for the same surface when different measurement methodologies are used. In this paper, a literature review is made that summarizes the problems encountered when parameterizing soil roughness as well as the reported impact of the errors made on the retrieved soil moisture. A number of suggestions were made for resolving issues in roughness parameterization and studying the impact of these roughness problems on the soil moisture retrieval accuracy and scale.

289 citations


Additional excerpts

  • ...(AIEM) [108])....

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References
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Book
01 Aug 1982
TL;DR: In this article, the authors present a model of a MICROWAVE REMOTE SENSING FUNDAMENTALS and RADIOMETRY, which is based on the idea of surface scattering.
Abstract: EN BIBLIOTECA: V.1: MICROWAVE REMOTE SENSING FUNDAMENTALS AND RADIOMETRY. V.2: RADAR REMOTE SENSING AND SURFACE SCATTERING AND EMISSION THEORY

3,501 citations


"Emission of rough surfaces calculat..." refers methods in this paper

  • ...HE TRADITIONAL models for wave scattering from random rough surfaces are the small perturbation method (SPM) and the Kirchhoff approximation (KA) [ 1 ]‐[4]....

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Book
01 Jan 1985
TL;DR: In this article, a vector radiative transfer equation for nonspherical particles is developed for both active and passive remote sensing of earth terrains, and the effective propagation constants and backscattering coefficients are calculated and illustrated for dense media.
Abstract: Active and passive microwave remote sensing of earth terrains is studied. Electromagnetic wave scattering and emission from stratified media and rough surfaces are considered with particular application to the remote sensing of soil moisture. Radiative transfer theory for both the random and discrete scatterer models is examined. Vector radiative transfer equations for nonspherical particles are developed for both active and passive remote sensing. Single and multiple scattering solutions are illustrated with applications to remote sensing problems. Analytical wave theory using the Dyson and Bethe-Salpeter equations is employed to treat scattering by random media. The backscattering enhancement effects, strong permittivity fluctuation theory, and modified radiative transfer equations are addressed. The electromagnetic wave scattering from a dense distribution of discrete scatterers is studied. The effective propagation constants and backscattering coefficients are calculated and illustrated for dense media.

1,398 citations

Book
28 Feb 1994
TL;DR: First-order radiative transfer solution passive sensing formulation of the surface scattering problem surface model and special cases ranges validity of the IEM model matrix doubling formulations for scattering and emission scattering and emissions models for snow and sea ice comparisons of model predictions with backscattering and emission measurements from snow and ice.
Abstract: First-order radiative transfer solution first-order radiative transfer solution passive sensing formulation of the surface scattering problem surface model and special cases ranges validity of the IEM model matrix doubling formulations for scattering and emission scattering and emissions models for snow and sea ice comparisons of model predictions with backscattering and emission measurements from snow and ice.

1,334 citations

Journal ArticleDOI
TL;DR: A backscattering model for scattering from a randomly rough dielectric surface is developed and both like- and cross-polarized scattering coefficients are obtained that satisfy reciprocity and contain only multiple scattering terms.
Abstract: A backscattering model for scattering from a randomly rough dielectric surface is developed. Both like- and cross-polarized scattering coefficients are obtained. The like-polarized scattering coefficients contain single scattering terms and multiple scattering terms. The single scattering terms are shown to reduce to the first-order solutions derived from the small perturbation method when the roughness parameters satisfy the slightly rough conditions. When surface roughnesses are large but the surface slope is small, only a single scattering term corresponding to the standard Kirchhoff model is significant. If the surface slope is large, the multiple scattering term will also be significant. The cross-polarized backscattering coefficients satisfy reciprocity and contain only multiple scattering terms. The difference between vertical and horizontal scattering coefficients increases with the dielectric constant and is generally smaller than that predicted by the first-order small perturbation model. Good agreements are obtained between this model and measurements from statistically known surfaces. >

1,190 citations


"Emission of rough surfaces calculat..." refers background or methods in this paper

  • ...By reformulating the above integral equations, an estimate of the tangential surface fields can be expressed as the sum of the Kirchhoff surface fields and the complementary surface fields [3], [ 9 ]....

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  • ...In the previous derivations [3], [ 9 ], the signs of absolute phase term in (9) and (10) were dropped, and the terms and in (2) and (4) were also dropped, in order to moderate the mathematical intricacy necessary to perform the power ensemble average....

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  • ...[5]‐[8] and the integral equation model (IEM) [3], [ 9 ]....

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Journal ArticleDOI
TL;DR: In this paper, a simple empirical model was proposed to describe the dielectric behavior of the soil-water mixtures and the model employed the mixing of either the Dielectric constants or the refraction indices of ice, water, rock and air, and treated the transition moisture value as an adjustable parameter.
Abstract: The recent measurements on the dielectric properties of soils have shown that the variation of dielectric constant with moisture content depends on soil types. The observed dielectric constant increases only slowly with moisture content up to a transition point. Beyond the transition it increases rapidly with moisture content. The moisture value at transition region was found to be higher for high clay content soils than for sandy soils. Many mixing formulas reported in the literature were compared with, and were found incompatible with, the measured dielectric variations of soil-water mixtures. A simple empirical model was proposed to describe the dielectric behavior of the soil-water mixtures. This model employs the mixing of either the dielectric constants or the refraction indices of ice, water, rock, and air, and treats the transition moisture value as an adjustable parameter. The calculated mixture dielectric constants from the model were found to be in reasonable agreement with the measured results over the entire moisture range of 0-0.5 cm3/cm3. The transition moistures derived from the model range from 0.16 to 0.33 and are strongly correlated with the wilting points of the soils estimated from their textures. This relationship between transition moisture and wilting point provides a means of estimating soil dielectric properties on the basis of texture information.

984 citations


"Emission of rough surfaces calculat..." refers background in this paper

  • ...The first dataset corresponds to moisture content ranging from 5% to 30% with dielectric constant from to [21], while the second one corresponds to moisture in volumetric water ranging from 5% to 40%, with dielectric constants ranging from to [ 22 ]....

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