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Geoscience and Remote Sensing, IEEE Transactions on

Issue 5 • Date Sept. 1985

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Displaying Results 1 - 25 of 27
  • IEEE Transactions on Geoscience and Remote Sensing

    Page(s): c1
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    Freely Available from IEEE
  • IEEE Geoscience and Remote Sensing Society

    Page(s): c2
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    Freely Available from IEEE
  • Table of contents

    Page(s): 613
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  • About the cover

    Page(s): 614
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  • A Tribute to the Late King-Sun Fu

    Page(s): 615
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  • Foreword

    Page(s): 616 - 617
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  • Influence of Aerosol Scattering on Atmospheric Blurring of Surface Features

    Page(s): 618 - 624
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    We investigate the influence of the shape of atmospheric scattering phase functions on blurring of surface detail in images acquired from space. The effects are characterized by computing atmospheric transfer functions and by solving the multidimensional equation of radiative transfer using a Fourier transform method. We predict that increased forward scattering enhances the detectability of atmospheric blurring near reflectance boundaries. Results for off-nadir viewing are also presented. View full abstract»

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  • The Relative Importance of Aerosol Scattering and Absorption in Remote Sensing

    Page(s): 625 - 633
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    Previous attempts to explain the effect of aerosols on satellite measurements of surface properties for the visible and near-infrared spectrum have emphasized the amount of aerosols without consideration of their absorption properties. In order to estimate the importance of absorption, the radiances of the sunlight scattered from models of the Earth-atmosphere system are computed as functions of the aerosol optical thickness and absorption. The absorption effect is small where the surface reflectance is weak, but is important for strong reflectance. These effects on classification of surface features, measuring vegetation index, and measuring surface reflectance are presented. View full abstract»

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  • Cloud Shadow Effects on Remote Sensing

    Page(s): 634 - 639
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    On relatively clear days, the shadow cast by an isolated, optically dense cloud produces an effect which is similar in extent and magnitude to the adjacency effects associated with high-contrast ground albedo boundaries. We have used a Monte Carlo radiative transfer model to examine the intensity and its components, comparing the cloud shadow case with that for a Lambertian albedo boundary. Although the behavior of the total intensity is nearly the same for both cases, the behaviors of the intensity components differ significantly. View full abstract»

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  • Two-Dimensional Leaf Orientation Distributions

    Page(s): 640 - 647
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    Combined inclination/azimuth leaf angle distributions are important for accurate models of vegetation canopy reflectance. It is shown that appropriate mathematical representations can be constructed from beta distributions under most circumstances. This is illustrated by analyzing observational data on soybean leaves and balsam fir needles. There are some problems when the data is imprecise and when correlations between inclination and azimuth angle are induced by heliotropism. Otherwise, the two-dimensional beta-type distribution appears to be a versatile tool for describing complete inclination/azimuth leaf angle distributions. View full abstract»

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  • Remote Sensing of Angular Characteristics of Canopy Reflectances

    Page(s): 648 - 658
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    The influence of the atmosphere on the remotely sensed angular distribution of canopy reflectance is studied by radiative transfer calculations with both a coupled atmosphere-canopy model and a pure atmosphere model with the canopy replaced by an equivalent bidirectional reflectance distribution function (BRDF). The canopy model, although one-dimensional, is able to reproduce typical canopy features like the "bowl shape" and the canopy "hot spot." In the decoupled mode, it can be used to compute canopy-equivalent BRDF's. The atmospheric perturbation of the angular reflectance pattern of a Lambertian, a mixed Lambertian/specular BRDF, and of the measured BRDF's of savannah and coniferous forest canopies is studied using one aerosol-free and two polluted atmospheres with surface visual ranges of V0 = 23 km and V0 = 5 km. It is shown that for surface albedoes > 10%, local extremes in the angular distribution of the surface reflectance and dependencies on the view azimuth angle are still detectable above the atmosphere and are nearly invariant to atmospheric perturbations. This result leads to the recommendation that off-nadir satellite observations in the near-infrared may contribute additional valuable information to crop identification. However, canopy reflectance variations with varying view zenith angles are dominated by atmospheric perturbations even for relatively clear atmospheres. View full abstract»

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  • Contrasts among Bidirectional Reflectance of Leaves, Canopies, and Soils

    Page(s): 659 - 667
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    The apparent brightness of a natural surface depends on the characteristics and direction of incident radiation, surface radiative properties, and the direction from which the surface is viewed. The bidirectional reflectance distribution functions (BRDF) for soils, vegetation canopies, and individual leaves have common features that arise from an anisotropic diffuse scattered component as well as specular reflections from irregular surfaces. The diffuse scattered component, however, tends to dominate canopy and soil BRDF's where as specular reflection tends to dominate leaf BRDF's. In this paper, simple models are presented for predicting soil and canopy BRDF's, and predicted results are compared with some measurements. This effort represents an attempt to illustrate the important features that cause observed BRDF's. The results of the models are compared with a simple three coefficient empirical equation that may be easier to invert than the causitive models so that radiation measurements can be used to obtain surface features. Some BRDF measurements from corn and soybean leaves provide a contrast for canopy and soil distributions, and also provide needed leaf properties that are important to vegetation canopy models. The knowledge of soil, canopy, and leaf BRDF's is combined into a single model, called Cupid, to predict the resultant BRDF of complex natural surfaces. View full abstract»

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  • A Monte Carlo Reflectance Model for Soil Surfaces with Three-Dimensional Structure

    Page(s): 668 - 673
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    A Monte Carlo soil reflectance model has been developed to study the effect of macroscopic surface irregularities larger than the wavelength of incident flux. The model treats incoherent multiple scattering from Lambertian facets distributed on a periodic surface. Resulting bidirectional reflectance distribution functions are non-Lambertian and compare well with experimental trends reported in the literature. Examples showing the coupling of the Monte Carlo soil model to an adding bidirectional canopy of reflectance model are also given. View full abstract»

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  • Evaluation of a Canopy Reflectance Model for LAI Estimation through Its Inversion

    Page(s): 674 - 684
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    A technique described earlier for estimating leaf area index (LAI) from bidirectional canopy reflectance (CR) data is applied and evaluated for three plant canopies-a naturally growing healthy soybean canopy and two orchardgrass canopies-one homogenous and the other spatially clumped or "tufted." This technique employs the inversion of a CR model which is chosen to be the SAIL model. The CR data were collected using a new ilstrument called the PARABOLA which is capable of acquiring the complete sky-and-ground looking hemisphere radiances in only 11 s. The model fit and LAI estimations for the soybean and uniform orchardgrass canopies are quite good. For the inhomogenous tufted orchardgrass canopy the LAI estimation is poor unless the maximum view zenith angle is restricted to 500. These results indicate that the biophysical parameter estimation from CR measurements may be applied with considerable confidence to homogenous herbaceous vegetation types but better CR models are needed to adequately represent discontinuous plant canopies. View full abstract»

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  • Microwave Inversion of Leaf Area and Inclination Angle Distributions from Backscattered Data

    Page(s): 685 - 694
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    The backscattering coefficient from a slab of thin randomly oriented dielectric discs over a flat lossy ground is used to reconstruct the inclination angle and area distributions of the discs. The discs are employed to model a leafy agricultural crop, such as soybeans, in the L-band microwave region of the spectrum. The distorted Born approximation, along with a thin disc approximation, is used to obtain a relationship between the horizontal-like polarized backscattering coefficient and the joint probability density of disc inclination angle and disc radius. Assuming large skin depth reduces the relationship to a linear Fredholm integral equation of the first kind. Due to the ill-posed nature of this equation, a Phillips-Twomey regularization method with a second difference smoothing condition is used to find the inversion. Results are obtained in the presence of 1 and 10 percent noise for both leaf inclination angle and leaf radius densities. View full abstract»

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  • Modeling the Radiant Transfers of Sparse Vegetation Canopies

    Page(s): 695 - 704
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    The three-dimensional radiative transfer model of Kimes [2] was used to extend our understanding of the physical principles causing the scattering dynamics in sparse vegetation canopies (¿ 50-percent ground cover). The model was upgraded by including an aniotropic scattering algorithm for soil developed by Walthall et al. [7]. The model was validated using measured directional reflectance data that covered the entire exitance hemisphere. Two canopies were chosen to present in this study-an orchard grass canopy (50-percent ground cover) and a hard wheat canopy (11-percent ground cover). These canopies showed the typical scattering behavior of canopies with low and intermediate vegetation density. A red wavelength (0.58-0.68 pm) band was used throughout the study. A number of phenomena contributed to the directional reflectance distributions observed in the field. These include: 1) the strong anisotropic scattering properties of the soil, 2) the geometric effect of the vegetation probability of gap function on the soil anisotropy and solar irradiance, and 3) the anisotropic scattering of vegetation which is controlled by the phase function (for an infinitely small volume of representative leaves) and geometric Effect 1 (cause by layering of leaves). These phenomena as identified in this paper account for the major scattering behavior of observed data sets of directional reflectance distributions. Such knowledge provides an intelligent basis for defining specifications of earth-observing sensor systems and for inferring important aspects of physical and biological processes of the plant system. View full abstract»

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  • Geometric-Optical Modeling of a Conifer Forest Canopy

    Page(s): 705 - 721
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    A geometric-optical forest canopy model that treats conifers as cones casting shadows on a contrasting background can explain the major portion of the variance in a remotely sensed image of a forest stand. The model is driven by interpixel variance generated from three sources: 1) the number of crowns in the pixel; 2) the size of individual crowns; and 3) overlapping of crowns and shadows. The model uses parallel-ray geometry to describe the illumination of a three-dimensional cone and the shadow it casts. Cones are assumed to be randomly placed and may overlap freely. Cone size (height) is distributed lognormally, and cone form, described by the apex angle of the cone, is-fixed in the model but allowed to vary in its application. The model can also be inverted to provide estimates of the size, shape, and spacing of the conifers as cones using remote imagery and a minimum of ground measurements. Field tests using both 10-and 80-m multispectral imagery of two test conifer stands in northeastern California produced reasonable estimates for these parameters. The model appears to be sufficiently general and robust for application to other geometric shapes and mixtures of simple shapes. Thus it has wide potential use not only in remote sensing of vegetation, but also in other remote sensing situations in which discrete objects are imaged at resolutions sufficiently coarje that they canot be resolved individually. View full abstract»

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  • Plant Canopy Specular Reflectance Model

    Page(s): 722 - 730
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    A model is derived for the amount of light specularly reflected and polarized by a plant canopy. The model is based on the morphological and phenological characteristics of the canopy and upon the Fresnel equations of optics. The theory demonstrates that the specular reflectance of the plant canopy is a function of the angle of incidence and potentially contains information to help discriminate between species. The theory relates the specular reflectance to botanical condition of the canopy-to factors such as development stage, plant vigor, and leaf area index (LAI). View full abstract»

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  • Inclusion of Specular Reflectance in Vegetative Canopy Models

    Page(s): 731 - 736
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    A detailed comparison of the observed soybeans and corn canopy reflectance with that calculated from three vegetative canopy reflectance models have shown systematic angular deviations. A likely cause of these effects is noninclusion of leaf specular reflectance. In this paper a formulation to calculate the component of canopy specular reflectance as a function of incident solar and view zenith angles, leaf area index, leaf angle distribution, and leaf specular reflectance has been developed. The SAIL model has been modified to include this conponent and the results are compared with an extensive observational data set on soybeans. It is shown that the systematic differences between the SAIL model and observations dependent on scattering azimuth are removed. An analysis of variance shows model improvement of 30 percent over the uncorrected SAIL model. View full abstract»

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  • Sources of Scattering from Vegetation Canopies at 10 GHz

    Page(s): 737 - 745
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    High-resolution backscatter measurements were made at X-band, with vertical polarization, and incidence angles of 30° and 50°, for winter wheat, soybeans, and corn during the summer of 1984. Plants were observed both under natural conditions and with partial-to-complete defoliation. The resolution volume of the measurement system is better than 20 × 20 × 11.25 cm3 within the entire range of measurements. Results are presented as a radar image, which also provides information on the spatial distribution of the (attenuated) scattering inside the canopy observed under natural conditions. Measured results indicate that: 1) for the full-grown wheat plants, heads are the dominant scatterers at the early heading stage and the ground is the dominant scatterer at the later growth stages; 2) for the soybeans, returns are mostly from the upper 30-cm portion of the plants, and leaves and stems dominate the radar signal at 30° and 50° incidence angles, respectively; 3) for the corn plants, leaves are the single dominan scatterers at both angles of incidence; and 4) ground returns are relatively unimportant as they are highly attenuated by the vegetation cover. View full abstract»

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  • Microwave Attenuation Properties of Vegetation Canopies

    Page(s): 746 - 753
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    A major impediment to the understanding and modeling of propagation through and backscattering and emission from vegetation canopies has been the lack of canopy attenuation data as a function of frequency, incidence angle, and polarization configuration. This paper presents the results of attenuation experiments conducted for canopies of winter wheat and soybeans in the late spring and early summer of 1984. Attenuation data were acquired at 1.55, 4.75, and 10.2 GHz for horizontal and vertical polarizations at incidence angles near 20° and 50°. In addition, wheat decapitation and soybean defoliation experiments were conducted to evaluate the relative importance of different canopy constituents (such as heads, leaves, and stalks) to the total canopy attenuation. The measured data were compared to calculations based on a model that treats the stalks as parallel elements of a uniaxial crystal and the leaves and branches as randomly oriented disks and needles, respectively. Very good agreement was obtained between theory and experimental observations for the soybean canopy for both polarizations and for the wheat canopy for vertical polarization; however, the model consistently underestimated wheat attenuation (relative to the data) for horizontal polarization. This deficiency of the model is attributed to the fact that it considers all the stalks to be vertically oriented, whereas in reality the stalks exhibit an orientation distribution, although it is centered around the vertical direction. View full abstract»

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  • Strong Fluctuation Theory for Scattering, Attenuation, and Transmission of Microwaves through Snowfall

    Page(s): 754 - 760
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    The strong fluctuation theory is applied to the study of the atmospheric snowfall which is modeled as a layer of random discretescatterers edium. As functions of size distribution, fractional volume, and radius of scatterers, we illustrate the relationship between the reflectivity factor and precipitation rate, the attenuation of the centimeter and millimeter waves, and the line-of-sight transmission of coherent and incoherent wave components. The theoretical results are shown to match favorably with experimental data. View full abstract»

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  • A Study of Backscattering and Emission from Closely Packed Inhomogeneous Media

    Page(s): 761 - 767
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    The effects of close spacing between small scattering spheres were examined by keeping the distance-dependent terms in the expressions for the transverse scattered fields. The phase matrix was then derived from these fields and was used in the radiative transfer formulation to model scattering and emission from a densely populated, inhomogeneous layer. Computed results were compared with those obtained when the phase matrix was specialized to the far-field condition. It was found that the use of the far-zone condition tended to underestimate both the level of the copolarized backscattering and the cross-polarized backscattering. In emission computations, the use of the far-zone condition overestimated the level of the brightness temperature. hese effecit decreased with a decrease in the volume fraction or an increase in the exploring frequency, as expected. An improvement on the snow parameter (density and crystal size) estimation was shown to be possible when this new phase matrix was used. View full abstract»

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  • A Comparison between Active and Passive Sensing of Soil Moisture from Vegetated Terrains

    Page(s): 768 - 775
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    A comparison between active and passive sensing of soil moisture over vegetated areas is studied via scattering models. In active sensing, three contributing terms to radar backscattering can be identified: 1a) the ground surface scatter term; 2a) the volume scatter term representing scattering from the vegetation layer; and 3a) the surfacevolume. scatter term accounting for scattering from both surface and volume. In emission, three sources of contribution can also be identified: 1b) surface emission, 2b) upward volume emission from the vegetation layer, and 3b) downward volume emission scattered upward by the ground surface. As ground moisture increases, terms 1a) and 3a) increase due to increase in permittivity in the active case. However, in passive sensing, term 1b) decreases but term 3b} increases for the same reason. This self-compensating effect produces a loss in sensitivity to change in ground moisture. Furthermore, emission from vegetation may be larger than that from the ground. Hence, the presence of vegetation layer causes a much greater loss of sensitivity to passive than active sensing of soil moisture. View full abstract»

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  • IEEE Geoscience and Remote Sensing Socity

    Page(s): 775-a
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    Freely Available from IEEE

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