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

Chapter

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

Document type:: Multivolume work

Structure type:: Chapter

LEAF REFLECTANCE A STOCHASTIC MODEL FOR ANALYSING THE BLUE SHIFT W. Lüdeker, K.P. Günther DLR - Oberpfaffenhofen, Institute of Optoelectronics, D- 8031 Wessling , West-Germany ABSTRACT In order to investigate the blue shift of the red edge in the reflectance spectra theoretically, the stocha stic leaf model of Tucker and Garratt (1977) was used. This approach treats the radiative transfer of dif fuse light as transitions of light with weighted probabilities according to the theory of homogeneous Markov processes with a finite number of states. The transition probabilities are determined by the opti cal parameters (e.g. specific absorption coefficients of different pigments, scattering coefficients and refractive index of cell membranes), the pigment concentrations and the geometrical dimensions of the leaf (e.g. total leaf thickness, thickness of palisade and spongy parenchyma and the geometrical cross section of chloroplasts and cells). Assuming realistic leaf parameters our results showed that the modeled reflectance spectra were not in agreement with measured data and the spectra presented by Tucker and Garratt (1977). Based on these findings the model was reinvestigated. By introducing a new radiation state and by revi sing the transition probabilities of Tucker and Garratt a successful modeling of reflectance spectra is possible assuming realistic leaf parameters. In order to investigate the blue shift of the red edge the model parameters were varied systematically. It was shown that - a reduced light absorption and / or - a shift in the absorption spectra of chlorophyll a. and b are responsible for the observed blue shift of the red edge. A reduced light absorption is not only caused by a reduced pigment concentration but also by a reduced light path. In turn the light path may be reduced by a decrease of the thickness of the palisade and / or spongy parenchyma or may be reduced by a decrease of the scattering coefficients. The shift of the absorption bands of chlorophyll a or b may occur to a minor extent when the chloro phyll-protein aggregates make a phase transition from polymeres to dimers or monomers due to environ mental stress. By traeting leaves with the herbicide DCMU in the laboratory the observed blue shift may be attributed to a shift of the absorption bands by partially extracting the chlorophyll pigments from the proteins. Key Words: Leaf reflectance, stochastic model, Markov chain, blue shift, red edge 1 INTRODUCTION Observing the reflectance spectra of vegetation in the visible domain a variation of the steep rise of the near-infrared reflection edge at about 690 nm can be seen. In the last few years the application of high resolution imaging spectroscopy stimulated the remote detection of this phenomenon, called the blue shift of the red edge, in order to monitor vege tative chlorophyll status and leaf area index inde pendently (Horler et al. 1983) and plant stress indu ced e.g. by geochemical metal deposition (Collins et al. 1983). The trace metal-induced stress retards the pigment synthesis and in turn decreases the pigment absorption leading to higher reflectance. Since the spectral shift is related not only to soil geochemi stry but also to tree species ( Singhroy et al. 1985) a uniform forest stand is best suited for studying the blue shift. A comparison of in situ and airborne spectral measurements of the blue shift in Vermont and West-Germany over homogeneous forest stands (Rock et al. 1988) showed that the blue shift is associated with damage in spruce needles. The au thors suggested that the shift of the red edge to shorter wavelengths may be due to an absorption li ne narrowing when the chlorophyll a concentration decreases in contrast to the explanation of a shift in the position of the maximum of the chlorophyll absorption. Also Buschmann and Lichtenthaler (1988) correlated the observed blue shift of the red edge

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