最新刊期
卷 ， 期 S1 ， 1997
- 摘要：This paper describes the principles and methodology to express bidirectional reflection （BDR） properties of ground targets by using direct radiative remotely sensed image under the support of GIS. The principles and theoretical basis is that the difference of slope and its orientation changes the relative position of pixel ground, sun, and satellite remote sensor and results in the variety of solar direct radiance of similar pixels. The difference reflect the bidirectional reflectance. The bidirectional reflectance could be studied through the analysis of the difference and its relation with sun position and satellite position under the support of GIS, using satellite remotely sensed direct radiance digital images.关键词：Direct radiance;Remotely sensed image;Bidirectional reflectance
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发布时间：2021-06-10 - 摘要：The image BRDF of forests and woodlands is a statistical function which operates at the scale of an average patch of cover rather than at the scale of crowns. Studies of the image Hotspot effect using aerial photography and high spatial resolution scanner data shows very high variance at this detailed scale. In addition, the directional effects of the sun and observer positions interact significantly to create an angular anisotropic variation which persists up to aggregated scales. This has been called the BRVF or Bidirectional Reflectance Variance Function. There has been a recent growing interest in the directional variance or variogram structure of high resolution images as a means to interpret structure and such data have become regularly flown. This work is an extension of the use of image variance to interpret structure as pioneered by Strahler and Li and explored by various authors over the last 15 years. Directional variograms and BRVF functions for forests at the crown scale can be computed using approximations to the overlap functions driving these second order statistics and compared with numerically integrated simulations. It has been shown that the scaling of BRVF and the anisotropy introduces into the variogram can be accurately modelled.关键词：Geometrical optical models;Canopy BRDF;Image variance;Variogram
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发布时间：2021-06-10 - 摘要：Because the relationship between LAI and NDVI is not unique and vary with structure of vegetation. We adopted NOAA-AVHRR images in the northern great plain to map distribution of the leaf area index（LAI）, average leaf angle（ALA） and so on, instead of using NDVI that is very popularly used in China. This paper first validated NK inversion algorithm using measurements of SE590 spectraradiometer in Yucheng Experimental Station. The optimum conditions for inversion are that view zenith ranged from 40 or so, view azimuth ranged -10 to 10.A comparison between inversion result and NDVI is conducted. There are two advantages to be obvious for using inversion algorithm of N-K model. 1) Ecologic parameters can be inverted directly without using correlation statistic method. 2) More than two parameters such as LAI , ALA, LAD can be obtained for n>2 inversion , whereas NDVI is just itself one parameters. 3) The bidirectional effect can be considered in the inversion algorithm , but NDVI can not. As a result, although improvement is necessary for the inversion algorithm in future , it is worth to test and apply that in wider range. 关键词：inversion;leaf area index;Simultaneous measurement
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发布时间：2021-06-10 - 摘要：ＰｒｅｓｅｎｔＳｔａｔｕｓａｎｄＰｅｒｓｐｅｃｔｉｖｅｓｏｆＲｅｍｏｔｅＳｅｎｓｉｎｇｏｆＶｅｇｅｔａｔｉｏｎＪｕｈａｎＲｏｓ（ＴａｒｔｕＯｂｓｅｒｖａｔｏｒｙ，ＥＥ２４４４Ｔｏｒａｖｅｒｅ，Ｔａｒｔｕ，Ｅｓｔｏｎｉａ）Ｄｕｒｉｎｇｔｈｅｒｅｃｅｎｔ...
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发布时间：2021-06-10 - 摘要：Vegetation cover attributes play a major role in surface energy budgets through their impact on photosynthetic processes and albedo. This paper presents a semiempirical approach to retrieve vegetation properties relevant for climate studies.The methods rely on multigular measurements and will rather apply to datasets of sensors systems such as POLDER in order to generate global maps of surface parameters.关键词：Surface parameters;Kerneldriven Models;Multiangular measurements
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发布时间：2021-06-10 - 摘要：Multiangular imagery is an important way of obtaining multiangular remotelysensed data. Before multiangular data can be used for analysis, it is important to register these data. Through registration, the same area can be identified from multiangular images. One of the problem in multiangular image registration is brightness variation due to differences in viewing angle, bidirectional reflectance variation and atmospheric scattering.In this paper, a series processing of registration for multiangular images will be described. It includes preprocessing and hierarchical brightnessbased registration algorithm. In order to remove the brightness differences between two images with large angle, we use an advanced template matching method which is not related to brightness mean to register images. Texture invariation will be considered. Along the viewing angle increasement direction, sequence registration can improve accuracy of large angle image registration. Finally, registration images were obtained by using local adaptive geometric correction.We use POLDER airborne simulated multiangular images which were provided by CNES of France and have obtained more than 30 differential angle registered data of rice and wheat, etc.关键词：Multiangular;Image registration.
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发布时间：2021-06-10 - 摘要：The research on monitoring the prairie harmed by mice and insects in the Ruoergai county with AVHRR data is presented in this paper. It shows that on the basis of application of the multiband spectrum, the application of multiangular remote sensing is more useful and improves the effect on distinguishing the ground objects and the areas harmed by mice and insects.关键词：AVHRR;Multiangular remote sensing;Harmed by mice and insects
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发布时间：2021-06-10 - 摘要：Several concepts for canopy hotspot measurements from space have been investigated. The most promising involves active illumination and bistatic detection that would allow hotspot angular distribution （BRDF） measurements from space in a searchlight mode. The concept includes a pointable illumination source, such as a laser operating at an atmospheric window wavelength, coupled with a number of high spatialresolution detectors that are clustered around the illumination source in space, receiving photons nearly coaxial with the retroreflection direction. Microwave control and command among the satellite cluster would allow orienting the direction of the laser beam as well as the focusing detectors simultaneously so that the coupled system can function like a search light with almost unlimited pointing capabilities. The concept is called the HotSpot SearchLight （HSSL） satellite. A nominal satellite altitude of 600 km will allow hotspot BRDF measurements out to about 18 degrees phase angle. The distributed are taking radiometric measurements of the intensity wings of the hotspot angular distribution without the need for complex imaging detectors. The system can be operated at night for increased signaltonoise ratio. This way the hotspot angular signatures can be quantified and parameterized in sufficient detail to extract the biophysical information content of plant architectures.关键词：HotSpot;Canopy BRDF;Plant architecture;Structural remote sensing signature;Satellite concept;Cluster
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发布时间：2021-06-10 - 摘要：Accurate measurements of snow areas and surface albedo are crucial to advancing our understanding of the global climate system. This is because of the highly reflective nature of snow combined with its large surface coverage （snow can cover up to 40% of the Earth’s land surface during the Northern Hemisphere winter）. The reflectance of snow varies with both solar incidence angle and the viewing angle. Visible sensors with different spatial resolutions have been used to infer the snow parameters. Currently, only nadir-viewing directional reflectance data are available from satellite observations. Observations at multiple angles are needed to infer the hemispheric reflectance albedo of snow fields.We propose to study the directional reflectance of snow fields using POLDER data, which contains information from different viewing angles and polarizations. POLDER was successfully launched on the ADEOS-1 satellite in August, 1996, however, because POLDER data are not yet available, data from ASAS, a pointable, airborne spectroradiometer, were used in this study. Data collected over Glacier National Park of Montana show strong angular dependence. Preliminary results confirm the anisotropic nature of the snow reflectance. Knowledge of the bi-directional reflectance function（BDRF） of snow-covered surfaces is the key to developing a true albedo model in the future.关键词：Snowpack;albedo;BDRF
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发布时间：2021-06-10 - 摘要：The role of Boreal forest biome in climate change has been investigated through the BOREAS experiment. Measurements of solar fluxes in conifer stands show important directional effects in the radiation field. These effects are mainly related to tree sarrangement and crown architecture. A simple model of direct transmittance can explain an important angular signature observed on the results.关键词：Radiation transfer measurements;Directional effects;Modeling
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发布时间：2021-06-10 - 摘要：Bidirectional reflectance measurement is very important in the BRDF model validation and inversion . For many reasons, there exists many errors in the measured data. As in the laboratory, there is no wind and cloud, thus the measured data is more stable than in vivo. These data have been used to validated and invert many BRDF models. A BRDF process system based on MS-Windows has been developed, which include measured bidirectional reflectance data management and preprocess, data 2D and 3D analysis, BRDF model validation, and model inversion . In this paper we chose four objects as test samples which are sparse dense cotton, cotton, soybean, and corn, to validate four empirical and semiempirical models which are Walthall,Roujean, Verstraete, Rahman model. The validated result fit measured data well. We also used SAIL model to try our inversion test. At first, the parameter sensitivity and their distribution in view positions were analyzed, the according to analysis result we determined three cases: the most sensitivity area, the least sensitivity area and principal plane. Finally, the SAIL model parameters LAI, LAD, ρ, τ were inverted in three cases . The results show that :1. The inversion of sensitive area is better than insensitive area. 2. The more sensitive model parameter is, the more precise and stable the inversion is. Therefore, whether a BRDF model model is invertable or not is not only depend on its mathematical invertibility, but also depend on what parameters you want to invert and what measured data you are using.关键词：Bidirectional reflectance measurement;Solar simulation laboratory;BRDF model inversion
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发布时间：2021-06-10 - 摘要：Physical BRDF models are usually very complex and difficult to invert. We usually need to employ a priori knowledge in this or that way, fix some parameter values and invert some others. Usually most of us agree that non-sensitive parameters should be fixed, but there has not been any consensus on how to define the sensitivity of a parameter in inversion. Li and Strahler, Li and Wang also suggested that only those the most sensitive and most uncertain parameters should be inverted by using a subset of observations, but they failed to spell out how to determine such “most sensitive and most uncertain” parameters and how to find such a subset of observations. This lacking of consensus and quantitative rules makes inversion of physical BRDF models a case-by-case “trick” or an “art but science”.We tried to develop a general framework for BRDF model inversion. It is based on accumulation of knowledge and an inversion strategy which we called Multi-stage, Sample-direction Dependent, Target-decisions （MSDT）.Our MSDT inversion strategy is based on an Uncertainty and Sensitivity Matrix （USM） of parameters at given directions/bands of observations. Its definition is somehow analogous to the partial derivative matrix used in Newton methods for minimization, but there are three significant differences: 1) the uncertainty of the initial guess is taken into account; 2) It is less dependent on the initial guess; 3) all elements have the same unit and therefore quantitatively comparable. An example of USM from Li-Strahler GOMS model and ASAS sampling will be presented, and it is obvious from the matrix what parameter should be inverted first, and what subset of observations should be used. In order to expressed the USM clearly for more complex sampling patterns, contours may be used .To demonstrate the MSDT strategy, we used Changping flight data to invert all the 7 parameters in Li-Strahler GOMS model using all the samples at the same time, then invert step by step depending on the USM-based MSDT, the effect is encouraging. 关键词：inversion;BRDF model
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发布时间：2021-06-10 - 摘要：The study focused on scaling the surface bidirectional reflectance of the rugged surfaces from fine to coarse spatial resolutions. Different bidirectional shadowing functions were compared with computer simulation techniques such as raytracing and radiosity based on the simulated surfaces and real 30 m Digital Elevation Model （DEM） data. All algorithms show that topography has significant effects on radiation scaling. However, comparisons also reveal large differences among models suggesting that further development is needed for accurate estimation of topographic effects on BRDFs.关键词：Topographic;Surface bidirectional reflectance;Radiation scaling
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发布时间：2021-06-10 - 摘要：Plant condition assessment using remote sensing techniques have been associated with spectral vegetation indices such as the normalized difference vegetation index （NDVI）. A change in NDVI values has been normally regarded as changes in vegetation amount or density. The spectral properties of plants, which are directly related to the health conditions, would also result in changes in spectral vegetation indices. Consequently, a lower vegetation index value may result from either lower density or nutrient stress, or a combination of the two. This would limit the use of vegetation indices as a monitoring tool. Bidirectional reflectance distribution function （BRDF） models treat plant density and optical properties differently and, therefore, can help to assess plant condition objectively. In this study, multiangular spectral reflectances were measured over two winter wheat canopies: one being under nitrogen stress and the other not. These multiangular measurements were then used in inversions of BRDF models to estimate the optical properties and the plant densities. The results show that it is feasible to obtain simultaneously the optical properties and plant densities and, therefore, it is possible to use BRDF models and multiangular remote sensing measurements to make diagnostic analysis of nitrogen-related plant conditions. The results also revealed some limitations of this approach such as inversion problems and computation time.关键词：BRDF;inversion;NDVI;Diagnostic assessments of plant condition
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发布时间：2021-06-10 - 摘要：This paper systematically studies the relationship between surface BRDF （Bidirectional Reflectance Distribution Function） retrieval and atmospheric correction. The study uses the atmospheric correction scheme of the Moderate Resolution Imaging Spectroradiometer （MODIS）, and angular sampling expected for MODIS and MISR （Multiangle Imaging SpectroRadiometer） for different land cover types and optical depths of aerosols. The results show that it is necessary to consider the surface anisotropic BRDF in atmospheric correction, and surface BRDF retrieval and atmospheric correction can be coupled in a converging iteration loop.关键词：Atmospheric correction;BRDF;MODIS
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发布时间：2021-06-10 - 摘要：ＲａｄｉｔａｔｉｖｅＴｒａｎｓｆｅｒｉｎＣｏｎｉｆｅｒｏｕｓＴｒｅｓＪｕｈａｎＲｏｓ，ＭａｄｉｓＳｕｌｅｖ（ＴａｒｔｕＯｂｓｅｒｖａｔｏｒｙ，ＥＥ２４４４Ｔｒａｖｅｒｅ，Ｔａｒｔｕ，Ｅｓｔｏｎｉａ）Ｉｎｔｈｅｔｈｅｏｒｙｏｆｔｈｅｒａｄｉａｔｉｏｎｔ...
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发布时间：2021-06-10 - 摘要：MISR is scheduled for launch in 1998 on the EOS AM1 platform. The algorithms needed to analyze data from this instrument are currently being tested, using both simulated data and data currently available from the airborne ASAS multiangle instrument. The data processing can be divided into three major, sequential segments. The first segment retrieves the necessary atmospheric properties over the scene. These results then are used in the second segment to retrieve the surface spectral HDRFs on a pixelby pixel basis for the scene. Finally, the HDRFs are used with a linearized three parameter BRF model in the third algorithm segment to retrieve the corresponding spectral BRFs. Results of the retrieval algorithms are presented using simulated MISR data. 关键词：ASAS multiangle instrument;The surface spectral HDRFs（hemisphericaldirectional reflectance factors）;BRF model;The Multiangle Imaging SpectroRaiometer（MISR）
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发布时间：2021-06-10 - 摘要：In our vegetation BRDF model and its application studies, we developed an indirect measuring method named the Tree Computed Tomography （TCT） for gathering tree crown architecture parameters, which include the Leaf Angle Distribution （LAD）, Foliage Area Volume Density （FAVD）, and Leaf Area Index （LAI）. With direct method in field, it is difficulty to measure this kinds of architecture parameters, especially for trees. The TCT algorithm combining both computed tomography theory and vegetation canopy gap probability model, makes the indirect method be possible in tree crown architecture measurement. To improve and validate the algorithm, the Tree Computed Tomography field data gathering System（TCTS） was designed for getting more reliable multiviewing points image set in field. Both coniferous and deciduous crowns were selected to do indirect and manual direct measurement to get crown architecture parameters for the validation. To improve our TCT algorithm, the average skylight distribution during the multiviewing points data gathering is reconstructed, the LAD estimation is considered, and the trunk/branches information is taken into account of FAVD reconstruction. Comparing the reconstructed 3d FAVD and manual measurement data, the results show that the reconstructed FAVD fit the manual measurement data very well. Then these indirect measured crown architecture parameters and measured radiance of lighted crown had been used in our BRDF model studies. This paper presents the above approach and the validation results.关键词：Computed tomography;Canopy structure;FAVD;LAI
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发布时间：2021-06-10 - 摘要：It is a report of experimental results. By means of the field measurements we obtained the features of variation of radiation reflectance （in wave bands 290-2800 nm and 400-700 nm） of the four components in GO approach in Juniperus tree nursery and the radiation transfer in a single tree crown and in apple tree orchard. At the same time we also obtained the foliage area volume density （FAVD） in three dimensions and the leaf angle distribution （LAD） with the Tree Computed Topography （TCT） method. The measured data of distribution of reflected radiation from sunlit crown of Junipers tree were related very well to the model calculation using the approach of path scattering of light in semi-infinite medium with modification of change the semi-infinite medium to the shape of tree crown.关键词：Field measurements;Variation of brightness of four components in GO approach;Radiation transfer in tree stand;Model validation
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发布时间：2021-06-10 - 摘要：In this paper we will discuss two uses of BRDFs in remote sensing: （1） in determining the clear sky top of the atmosphere （TOA） albedo, （2） in quantifying the effect of the BRDF on the adjacency pointspread function and on atmospheric corrections. The TOA spectral albedo is an important parameter retrieved by the Multiangle Imaging SpectroRadiometer （MISR）. Its accuracy depends mainly on how well we can model the surface BRDF for many different situations. We will present results from an algorithm which matches several semiempirical functions to the nine MISR measured BRFs that are then numerically integrated to yield the clear sky TOA spectral albedo in four spectral channels. We show that absolute accuracies in the albedo of better than 1 % are possible for the visible and better than 2 % in the near infrared channels. Using a simplified extensive radiosity model, we will show that the shape of the adjacency pointspread function （PSF） depends on the underlying surface BRDFs. The adjacency pointspread function at a given offset （x,y） from the center pixel is given by the integral of transmissionweighted products of BRDF and scattering phase function along the line of sight. 关键词：Clear sky albedo;BRDF;Adjacency effect;Atmospheric point spread function
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发布时间：2021-06-10 - 摘要：This paper focuses on the evaluation of a new model of radiation transfer in heterogeneous threedimensional media, based on the Monte Carlo ray tracing technique. This model is conceived as a virtual laboratory, where the targets can be individually characterized, and where the interactions between the radiation field and these targets can be explicitly controlled. The model can be used to generate reflectances as well as absorption profiles for arbitrarily complex threedimensional targets, such as an individual plant leaf or a complete forest canopy. The model performance is evaluated by comparing model simulations with laboratory measurements obtained over an artificial target. Observations have been carried out by the Advanced Techniques unit of the Space Applications Institute in the European goniometer （EGO） facility. Comparisons with laboratory measurements demonstrate the capability of our model to reproduce the actual observed reflectance factors of a fully documented target, and even to characterize the performance of this laboratory.关键词：Monte Carlo;ray tracing;Goniometer measurements;Radiative’transfer modeling
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发布时间：2021-06-10 - 摘要：At present NOAAAVHRR can offer us many multiangle earth observation data.through careful collection of successive AVHRR images, the existence of nonLambertian effect had been proven. Its relative variance will not be larger than 30%. It is not surprising large,but it can not be neglected too. This paper reports an initial study about how to correct the nonLambertian effect through building up BRDF models for vegetation and soil background and with the help of decomposing method of mixed pixel.Results show our method is basically correct and practical. Further study is still needed because of the effect of nonLambertian mixed with other problems, such as atmospheric correction.关键词：NonLambertian effect;BRDF models;Decomposing method of mixed pixel
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发布时间：2021-06-10 - 摘要：Existing forest reflectance models have already demonstrated their ability to be used to interpret remotely sensed data on forests in the nadir view direction. With the appearance of new possibilities to measure the multiangular reflectance characteristics, the interest to simulate forest reflectance in any view direction has increased. The cited models are capable to produce the angular distribution of reflectance, too, however, this possibility has been little used so far. Below some results of simulation of angular distribution of reflectance by the model described in are presented.关键词：BDRF;The angular distribution of reflectance
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发布时间：2021-06-10 - 摘要：The POLDER instrument （POLarization and Directionality of Earth Reflectances） flew during the BOREAS experiment onboard a C130 aircraft from NASA. BRDF measurements were obtained by POLDER on various supersites in the South area of the BOREAS. Large hot spot features over forest covers, and specular components over fen areas are described. The paper quantifies with airborne POLDER data the improvement of classification and discrimination of various forest covers when remotelysensed directional signatures are added to the more conventional spectral signatures. When using non supervised classifications, the terms of interclass confusion matrices are much lower （by a factor between 2 and 5） when directional information is added to the conventional spectral information. This proves that directional signatures enhance the discrimination of boreal forest covers by remote sensing.关键词：POLDER instrument （POLarization and Directionality of Earth Reflectances）;Hot spot;Directional signatures
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发布时间：2021-06-10 - 摘要：Analytical canopy reflectance （CR） models have reached the level of adequacy that makes it possible to estimate vegetation parameters by the inversion of such models. The increasing efficiency of algorithms, and the increasing power of computers incite to develop procedures for the estimation of vegetation phytometrical parameters on large areas using satellite data and the inversion of theoretical CR models. A Markov chain canopy reflectance model （MCRM） by Kuusk demonstrated its ability to work on wide range of canopy optical and structural parameters even in the case of serious violations of model assumptions . The MCRM is very computer-efficient and can be easily inverted on relatively large sets of reflectance data. Canopy reflectance models relate canopy directional reflectance to canopy structural and optical parameters. In order to solve the inverse problem on satellite images, we have to convert digital counts of satellite radiometers to ground level reflectances. For the conversion it is necessary 1) to determine satellite level radiances, i.e. to perform absolute calibration of radiometers, and 2) to estimate the ground level reflectance of targets, i.e. to perform atmospheric correction of satellite data. A straightforward procedure of pixel-by-pixel inversion of satellite images is possible, however, the inversion time increases rapidly with increasing image size and increasing number of spectral channels. The CR model inversion on large images can be performed more efficiently if some clusterization in the space of spectral signatures is applied. Here the MCR model is inverted on a 256×256 Landsat Thematic Mapper （TM） scene of a test site in Estonia. The spectral images of TM2, TM3, TM4, TM5 and TM7 taken on 8th June 1988 are used. 关键词：Canopy reflectance model;Markov chain;inversion;Chorophyll content
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发布时间：2021-06-10 - 摘要：The present paper applies the approach using ocean and cloud views to calibrating absolutely visible and nearinfrared channels of the AVHRR on board NOAA14. The results of the absolute calibration of the two channels demonstrate that the AVHRR channels 1 and 2 sensors have been deteriorated and show a degradation 7 percent and 11 percent, respectively, with respect to the preflight calibration. To verify the results of the absolute calibration, the ground measured spectral reflecnces in desert area in China have been appled to campare with the satellite data corrected by the calibration coefficients. Agreement within an error of measurement has been found between the ground measured reflectances and the corrected satellite data for NOAA-14. Both very high and very low reflectances have been used in the calibration approach, so that the calibration coefficients can be applied to the various sites with different reflective properties. 关键词：Quantification of satellite data;Atmospheric correction;Radiative calibration
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发布时间：2021-06-10 - 摘要：The Ambrals BRDF model which will be used to process the BRDF/Albedo product from data from the forthcoming EOS MODIS and MISR instruments is used to model directional reflectance data of the Sahel from AVHRR data. The model proves to be capable of describing the observed data well. Issues related to kernel selection and information content of the derived model parameters are addressed.关键词：BRDF;HAPEX sahel;AVHRR
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发布时间：2021-06-10 - 摘要：A 16day standard BRDF and albedo product will be produced from combined MODIS and MISR data at a spatial resolution of 1km. This paper demonstrates that BRDF and albedo retrieval accuracies from simulated MODIS/MISR angular sampling are within 5 to 10 percent in the majority of sampling situations.关键词：Bidirectional reflectance;albedo;MODIS;EOS
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发布时间：2021-06-10 - 摘要：In this study, the estimation of the Bidirectional Reflectance Distribution Functions （BRDFs） for selected land cover types was made by using the airborne POLDER image data. The main results in this study can be summarized as follows:（1） We presented an specially improved atmospheric correction algorithm , applicable to a framed image data by the POLDER sensor. The terrestrial images measured successively by the airborne POLDER with a different viewing angle were converted to a series of surface albedo images by our atmospheric correction method, in which the multiple scattering were taken into account for.（2） Then, the spectral BRDFs for selected 21target areas, including the cover types of River, Pond,City, Road, Forest were estimated from using successive albedo images. It was found that the BRDF for water surfaces follow a Lambertian law at both 550nm, 650nm and at 850nm. It was also found that the BRDFs for vegetated surfaces are more or less isotropic at 550nm and 650nm, but they are anisotropic at 850nm. The fitting parameters of the empirical BRDF law for all of target surfaces were presented.关键词：POLDER;BRDF;Atmospheric correction;multiple scattering
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发布时间：2021-06-10 -
Parameterization of Spectral Component Signatures for Geometric Optical Canopy Reflectance Modeling
摘要：A hybrid geometric optical and radiative transfer approach is used to parameterize the four component spectral signatures （sunlit crown, sunlit background, shaded crown, and shaded background） in geometric optical reflectance models over discontinuous plant canopies. The path scattering parameters （transmittance and reflectance） are estimated using a modified version of the analytical solutions of path scattering parameters （reflectance and transmittance） for a homogeneous medium layer, which includes the effect of the canopy gaps. The spectral component signatures are functions of the transmittance and reflectance for discontinuous plant canopies, the background albedo and the proportions of incident beam and diffuse skylight. The modeled spectral component signatures show good agreement with data collected in a conifer forest in Holland, Maine. Using the parameterized spectral component signatures, estimates from Li and Strahler’s geometric optical mutual shadowing model for directional reflectance over the old jack pine and old black spruce forests in the boreal ecosystematmosphere study （BOREAS）, match well with PARABOLA measurements at different solar and viewing geometry.关键词：Parameterization of the spectral signatures;GO models- 128
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发布时间：2021-06-10 - 摘要：The Leaf Angle Distribution （LAD） and Leaf Area Index （LAI） are important descriptors of the vegetation canopy. But direct field measurement of these variables is very labor-intensive and timeconsuming because of the complexity and variation in canopy architecture within and between species, especially for conifers. Upward-looking fisheye photos have been used to provide LAI estimates, but such estimates are subject to errors caused by unknown LAD and clumping of leaves and branches. In this paper, we present our new method on LAD and LAI estimation. The main approach is on how to introduce our intercrown gap probability model into LAI and LAD inversion algorithm, to express the effect of viewing direction on clumping index in normal gap probability model. Two validation experiments have been done. In one of them the estimated LAD （10-degree grouping） fits the directly measured LAD with a correlation coefficient 0.97. Another result is similar. Although the primary results are encouraging, more validation, especially under natural forest, are still needed to incorporate the method into our tree tomography procedure.关键词：Coniferous canopy;Directional gap probability;LAD;inversion
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发布时间：2021-06-10 - 摘要：A remote observation of any plant canopy derives from the collective effect of all the individual component parts including leaves, stems, flowers, and the soil background when the canopy is sparse. Therefore, canopy remote signatures can best understood by characterizing at least the most important components. The most important radiative components in live vegetation are leaves. The partitioning of radiation as reflectance transmitted , or absorbed energy depends on a number of factors including leaf cellar structure, leaf pubescence and roughness, leaf morphology, and leaf surface characteristics. Reflectance from leaves can be thought of as having both Lambertian （diffuse） and nonLambertian （specular） components. The diffuse, Lambertain character of leaf reflectance emanates primarily from the interior of the leaf through multiple scattering. The specular and nonLambertain character of the leaf reflectance arises at the surface of the leaf.In this paper, we introduce a laboratory goniometer, which was designed and built to measure and model light scattered by individual plant leaves. Goniometric measurements were taken during the summer of 1995 on individual plant leaves of soybean, corn, cotton in Changchun. Source wavebands selected were VIS band （600-690nm） and NIR band （690-760nm）, and three illumination angles were used, 20°,40°, and 60° from the normal on both the adaxial（top） and abaxial（bottom） side of leaves. View zenith angles are also used, 20°,40°, and 60° for every incident angle. Reflected radiation was measured at 10° increments between 0° and 350° along view zenith angles and illumination angles. The polaroids of0° and 90° are used to investigate polarized reflectance of leaf in the visible and near infrared wavelength ranges. These results shows the leaf BRDF depends strongly on wavelength, and, has a marked dependence on source incidence angle, view zenith angle and view azimuth angle. The bidirectional reflectance characteristics of individual leaves should be useful in formulating mathematical representations of nonLambertian leaf properties in radiative transfer models, and this work be continued further to obtain detailed information for s variety of species and leaf conditions.关键词：BRDF;Back reflectance;Face reflectance;Specular reflectance;Diffuse reflectance
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发布时间：2021-06-10 - 摘要：The interpretation of satellite remote sensing data in terms of land surface properties requires the use of radiation transfer models and inversion procedures. Various approaches are briefly mentioned, including Monte Carlo ray tracing, physicallybased 1D models, and parametric formulations capable of representing the general anisotropic behavior of natural surfaces. Some of the assumptions made in each approach, as well as their implications are reviewed, and the intrinsic difficulty of dealing with radiation transfer in a medium as inhomogeneous as a plant canopy is underscored. The need to pursue further research to take full advantage of the upcoming generation of advanced Earth Observation sensors is stressed.关键词：inversion;Radiation transfer;Bidirectional reflectance
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发布时间：2021-06-10
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