The role of canopy structure in the spectral variation of transmission and absorption of solar radiation in vegetation canopies

Panferov, O.; Knyazikhin, Yuri; Myneni, Ranga B.; Szarzynski, Joerg; Engwald, Stefan; Schnitzler, K.-G.; Gravenhorst, G.

doi:10.1109/36.905232

Cited by 110 publications

(78 citation statements)

References 22 publications

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“…We have also masked spectral measurements at wavelengths longer that 2000 nm because the clear sky values of zenith radiance at these wavelengths are too low and too uncertain to be used as a denominator in equation (4). observed and physics behind such phenomena have been documented [Panferov et al, 2001, Huang et al, 2007, Knyazikhin et al, 1998]. The slope and intercept of the relationships are indicative of canopy micro-and macroproperties [Smolander and Stenberg, 2005;Lewis and Disney, 2007].…”

Section: Spectrally-invariant Functionmentioning

confidence: 99%

“…The important questions we address are: what are the fullspectral radiative characteristics of the clear-cloud transition zone; and what is the spectral signature of a weak evaporating cloud? We will also show that SWS observations of the transition zone have wavelength-independent characteristics that were earlier observed in reflectance spectra of vegetated surfaces [Knyazikhin et al, 1998;Panferov et al, 2001]. Finally, we discuss how spectral invariant characteristics can be used to study the transition zone.…”

Section: Introductionmentioning

confidence: 99%

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Spectral invariant behavior of zenith radiance around cloud edges observed by ARM SWS

Marshak¹,

Knyazikhin²,

Wiscombe³

2009

Geophysical Research Letters

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[1] The ARM Shortwave Spectrometer (SWS) measures zenith radiance at 418 wavelengths between 350 and 2170 nm. Because of its 1-sec sampling resolution, the SWS provides a unique capability to study the transition zone between cloudy and clear sky areas. A spectral invariant behavior is found between ratios of zenith radiance spectra during the transition from cloudy to cloud-free. This behavior suggests that the spectral signature of the transition zone is a linear mixture between the two extremes (definitely cloudy and definitely clear). The weighting function of the linear mixture is a wavelength-independent characteristic of the transition zone. It is shown that the transition zone spectrum is fully determined by this function and zenith radiance spectra of clear and cloudy regions. An important result of these discoveries is that high temporal resolution radiance measurements in the clear-to-cloud transition zone can be well approximated by lower temporal resolution measurements plus linear interpolation.

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Section: Spectrally-invariant Functionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Spectral invariant behavior of zenith radiance around cloud edges observed by ARM SWS

Marshak¹,

Knyazikhin²,

Wiscombe³

2009

Geophysical Research Letters

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“…Scaling is defined as the process by which we establish that the LAI/ FPAR values derived from coarse resolution sensor data are the arithmetic averages of LAI/FPAR values derived inde- pendently from fine resolution sensor data over the same region (Tian et al, in press). The variables p t and p a , which imbue scale dependence to the algorithm via modifications to the LUTs, can be derived from model calculations and measurements of leaf and canopy spectral properties (Panferov et al, 2001). Ground-based measurements that allow specification of p t and p a are included in a prioritized list of measurements needed for validation of MODIS LAI/FPAR product.…”

Section: Safari-2000 West Season Campaignmentioning

confidence: 99%

Global products of vegetation leaf area and fraction absorbed PAR from year one of MODIS data

Myneni

Hoffman

Knyazikhin

et al. 2002

Remote Sensing of Environment

1,699

1,150

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An algorithm based on the physics of radiative transfer in vegetation canopies for the retrieval of vegetation green leaf area index (LAI) and fraction of absorbed photosynthetically active radiation (FPAR) from surface reflectances was developed and implemented for operational processing prior to the launch of the moderate resolution imaging spectroradiometer (MODIS) aboard the TERRA platform in December of 1999. The performance of the algorithm has been extensively tested in prototyping activities prior to operational production. Considerable attention was paid to characterizing the quality of the product and this information is available to the users as quality assessment (QA) accompanying the product. The MODIS LAI/FPAR product has been operationally produced from day one of science data processing from MODIS and is available free of charge to the users from the Earth Resources Observation System (EROS) Data Center Distributed Active Archive Center. Current and planned validation activities are aimed at evaluating the product at several field sites representative of the six structural biomes. Example results illustrating the physics and performance of the algorithm are presented together with initial QA and validation results. Potential users of the product are advised of the provisional nature of the product in view of changes to calibration, geolocation, cloud screening, atmospheric correction and ongoing validation activities. D

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“…Secondly, we estimated the shoot-specific but wavelength independent parameter p sh , corresponding to the probability that a photon scattered from the needle surface of the shoot will interact with the shoot again. The parameter p sh is conceptually similar to the canopy structural parameter ( p i , probability of interaction) defined by Knyazikhin et al (1998), which links together canopy absorptance and scattering at any two different wavelengths (Panferov et al, 2001). In thermal engineering, a similar concept is known as view factor or shape factor, giving the proportion of radiation emitted from a body that hits the body again (e.g.…”

Section: Introductionmentioning

confidence: 99%

A method to account for shoot scale clumping in coniferous canopy reflectance models

Smolander¹,

Stenberg²

2003

Remote Sensing of Environment

126

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The three-dimensional structure of a coniferous shoot gives rise to multiple scattering of light between the needles of the shoot, causing the shoot spectral reflectance to differ from that of a flat leaf. Forest reflectance models based on the radiative transfer equation handle shoot level clumping by correcting the radiation attenuation coefficient with a clumping index. The clumping index causes a reduction in the interception of radiation by the canopy at a fixed leaf area index (LAI). In this study, we show how within-shoot multiple scattering is related to shoot scale clumping and derive a similar, but wavelength dependent, correction to the scattering coefficient. The results provide a method for integrating shoot structure into current radiative transfer equation based forest reflectance models. The method was applied to explore the effect of shoot scale clumping on canopy spectral reflectance using simple model canopies with a homogeneous higher level structure. The clumping of needles into shoots caused a wavelength dependent reduction in canopy reflectance, as compared to that of a leaf canopy with similar interception. This is proposed to be one reason why coniferous and broad-leaved canopies occupy different regions in the spectral space and exhibit different dependency of spectral vegetation indices on LAI. D

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The role of canopy structure in the spectral variation of transmission and absorption of solar radiation in vegetation canopies

Cited by 110 publications

References 22 publications

Spectral invariant behavior of zenith radiance around cloud edges observed by ARM SWS

Spectral invariant behavior of zenith radiance around cloud edges observed by ARM SWS

Global products of vegetation leaf area and fraction absorbed PAR from year one of MODIS data

A method to account for shoot scale clumping in coniferous canopy reflectance models

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