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:: ESTIMATION OF WINTER WHEAT GREEN LEAF AREA INDEX FROM FIELD SPECTROSCOPIC MEASUREMENTS USING A SEMI-DETERMINISTIC MODEL. Robert DE WULF and Roland GOOSSENS, Georges HOFMAN

Document type:: Multivolume work

Structure type:: Chapter

467 « (o), imam * (o), trema püque lerosol " a ESTIMATION OF WINTER WHEAT GREEN LEAF AREA INDEX FROM FIELD SPECTROSCOPIC MEASUREMENTS USING A SEMI-DETERMINISTIC MODEL Robert DE WULF and Roland GOOSSENS Laboratory of Remote Sensing and Forest Management, Gent State University Coupure 653, B-9000 Gent, Belgium Georges HOFMAN Laboratory of Agricultural Soil Science, Gent State University Coupure 653, B-9000 Gent, Belgium ABSTRACT A comprehensive experiment to estimate green Leaf Area Index (LAI) of winter wheat (Triticum aestivum L.) from field spectroscopic measurements spanning four growing seasons (1984, 1985, 1986 and 1988) and involving three cultivara was conducted. Ground-based colour-infrared photography was the field spectroscopic method selected to acquire winter wheat canopy reflectance data. Seven types of 'vegetation index' were calculated. Correction procedures for solar zenith angle were introduced as experimental variable. Based on biophysical considerations, the monomolecular function was selected to model the relationship between vegetation indices and winter wheat LAI. Different models were constructed for pre-senescence and post-senescence data. Independent test data were used to assess the effectiveness of the prediction equations constructed from the training data. It is concluded that, despite obvious inaccuracies for large LAI values, the monomolecular function is an appropriate model to describe the relationship between winter wheat green LAI and vegetation indices. Ratio indices are better estimators of LAI than are orthogonal indices. For pre-senescence conditions, the Simple Ratio, Normalized Difference and TSAVI yield accurate and comparable results across cultivara and growing seasons. Post-senescence LAI is more difficult to estimate, and the Simple Ratio is the only valid vegetation index across cultiváis and seasons. A correction for solar zenith angle involving the normalisation of LAI yielded consistent good results. Key Words : Winter deterministic model. 1. INTRODUCTION The use of leaf area as the description parameter in crop growth analysis was pioneered by Watson (1956) who defined it as "the area of leaf laminae per unit area of land surface ". The magnitude and duration of LAI is strongly related to the canopy's ability to intercept photosynthetically active radiation (PAR). Therefore, LAI is correlated with canopy photosynthesis and dry matter accumulation in situations where stress does not predominate. The importance of an accurate estimation of LAI for crop growth studies needs not to be stressed. Manual field methods involving cutting, sorting and weighing or planimetering are destructive and extremely tedious. In addition, in view of statistical considerations, they are not necessarily more accurate. For instance, Curran and Williamson (1985) showed that errors in ground data collection are likely to exceed the error in the remotely sensed data. Paradoxically, this would make remotely sensed data more accurate than the ground data used to check its accuracy. The rationale behind the use of multispectral reflectance data in wheat, Leaf Area Index, Vegetation Index, Semi- general, and of vegetation indices (VI) in particular, to estimate crop LAI has been established for some time. Canopy reflectance patterns in single bands lead to an explanation for the usefulness of Vi's as estimators of LAI. High absorption in the green and red wavebands causes rapid saturation in function of increasing LAI and occurs around LAI values of 2. On the other hand, near infrared (NIR) reflectance initially continues to increase at higher LAI levels due to multiple scattering between vegetative layers before eventually reaching an asymptotic level termed infinite reflectance, coinciding with a LAI value of about 8 (Wiegand et al. 1979) . From these considerations it follows that the relationships between LAI and Vi’s are basically non-linear. A multitude of empirical relationships between LAI and Vi's have been documented in literature. In view of a more operational use of these relationships, an investigation of a single model that would be valid across growing seasons and cultivars appears to be justified. For this type of exercise, field spectroscopy methods are eminently suited (Milton 1987). a»«® <4É¡ÍbÍS¡S «fett iM ; I Ipi IWL, tPHII . >üüüi ïjpgl Ip » Imm

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