Proceedings of the Symposium on Global and Environmental Monitoring: Proceedings of the Symposium on Global and Environmental Monitoring

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Persistent identifier:: 856665355

Title:: Proceedings of the Symposium on Global and Environmental Monitoring

Sub title:: techniques and impacts ; September 17 - 21, 1990, Victoria Conference Centre, Victoria, British Columbia, Canada

Year of publication:: 1990

Place of publication:: Victoria, BC

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 856665355

Language:: English

Document type:: Multivolume work

Volume

Persistent identifier:: 856669164

Title:: Proceedings of the Symposium on Global and Environmental Monitoring

Sub title:: techniques and impacts; September 17 - 21, 1990, Victoria Conference Centre, Victoria, British Columbia, Canada

Scope:: XIV, 912 Seiten

Year of publication:: 1990

Place of publication:: Victoria, BC

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 856669164

Illustration:: Illustrationen, Diagramme, Karten

Signature of the source:: ZS 312(28,7,1)

Language:: English

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Editor:: International Society for Photogrammetry and Remote Sensing, Commission of Photographic and Remote Sensing Data

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2016

Document type:: Volume

Collection:: Earth sciences

Chapter

Title:: [WP-4 INTERPRETATION AND MODELLING]

Document type:: Multivolume work

Structure type:: Chapter

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Title:: LEAF REFLECTANCE A STOCHASTIC MODEL FOR ANALYSING THE BLUE SHIFT. W. Lüdeker, K. P. Günther

Document type:: Multivolume work

Structure type:: Chapter

479 Figures 3 and 4 show the development of leaf re flectance from the early beginning in May when the buds are broken and the leaves are light-green. With the increasing pigment concentrations from May 15 to June 1 the reflectance spectrum changes dra matically. In the blue region of the spectrum the flattening of the reflectance spectrum is observed due to the saturation of the absorption. The chloro- plasts are no more transparent in the blue absorbing all incoming light. In the red part of the spectrum a linear decrease of the reflectance is seen associated with the shift of the red edge towards longer wave lengths. When the leaf is dark green at July 1 the reflectance spectrum does not change remarkable in the blue. In contrast the green to red domain of the reflectance decreases. At about 680 nm, the maxi mum of the chlorophyll a absorption, the reflectance flattens due to saturation and absorption line broa dening resulting in an additional shift of the red edge. Figure 3: Saisonal cycle of the reflectance spectra of the model leaf 1: reflectance, when buds are broken, May, 15 2: reflectance at June,l 3 reflectance at September, 1 4 Figure 4: Saisonal cycle of the reflectance spectra of the model leaf 4. reflectance at September, 15 5: reflectance at October, 1 During summer, the pigment concentration remains relativ constant. As seen in figure 4, the reflectance spectrum for September 15 is comparable with the spectrum from July 1. During the next two weeks, the chlorophyll concentration breaks down accompa nied by an increase of a new pigment, the anthocya- nin. This pigment occurs during the autumn and is localized in the vacuoles of the epidermis. Due to the strong absorption of anthocyanin in the 500nm to 600nm region the green reflectance decreases while the reflectance in the domain of the red edge increases leading to the typical red coloring of lea ves during autumn. A comparison with the measured reflectance spectra during autumnal leaf coloring (Boyer et al. 1988) shows good agreement with our calculated spectra. The only major difference is seen again in the near- infrared region due to the constancy of the scatte ring coefficient used in the model. 4 CONCLUSION Based on the experimental findings and the different interpretations of several investigators (Boyer et al. 1988, Buschmann and Lichtenthaler 1988, Collins et al. 1983, Horler et al. 1980, Horler et al. 1983, Rock et al. 1988, Schutt et al. 1984, Singhroy et al. 1985), that the blue shift of the red edge of the reflectan ce spectrum of vegetation may be correlated with the vegetative chlorophyll status, the species, the developmental stage, the leaf surface exposed to the sensor, the water content and the chlorophyll fluo rescence, the stochastic model of Tucker and Garratt (1977) was reinvestigated in order to find a theoreti cal, bio-optical approach for a comprehensive inter pretation of all the different explanations. In a revised version the stochastic leaf model de monstrated its potential to calculated the reflectan ce spectrum of vegetation. Optical, geometrical and physiological parameters as e.g. the specific absorp tion coefficient of chlorophyll a,, the pigment con centration and the leaf thickness are used as input parameters. The revised model takes into account different mechanisms as absorption, reflection and Mie scattering at the chloroplasts and the leaf cells. According to our first results showing good agree ment with data from the literature, the model pre sents two ways for interpreting the blue shift. First, by reducing the light absorption in the leaf, a blue shift of the red edge can be produced because the absorption line in the red part of the spectrum narrows. In turn a reduced light absorption can be modeled twofold by reducing the pigment concen tration of the leaf or by reducing the thickness of the leaf assuming constancy of the pigment concen tration. Thinner leaves have in general a shorter light path resulting in an overall less absorption.

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