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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 14
Biogeosciences, 12, 4509-4523, 2015
https://doi.org/10.5194/bg-12-4509-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: EUROSPEC – spectral sampling tools for vegetation biophysical...

Biogeosciences, 12, 4509-4523, 2015
https://doi.org/10.5194/bg-12-4509-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Reviews and syntheses 30 Jul 2015

Reviews and syntheses | 30 Jul 2015

Reviews and Syntheses: optical sampling of the flux tower footprint

J. A. Gamon J. A. Gamon
  • Department of Earth & Atmospheric Sciences, and Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada

Abstract. The purpose of this review is to address the reasons and methods for conducting optical remote sensing within the flux tower footprint. Fundamental principles and conclusions gleaned from over 2 decades of proximal remote sensing at flux tower sites are reviewed. The organizing framework used here is the light-use efficiency (LUE) model, both because it is widely used, and because it provides a useful theoretical construct for integrating optical remote sensing with flux measurements. Multiple ways of driving this model, ranging from meteorological measurements to remote sensing, have emerged in recent years, making it a convenient conceptual framework for comparative experimental studies. New interpretations of established optical sampling methods, including the photochemical reflectance index (PRI) and solar-induced chlorophyll fluorescence (SIF), are discussed within the context of the LUE model. Multi-scale analysis across temporal and spatial axes is a central theme because such scaling can provide links between ecophysiological mechanisms detectable at the level of individual organisms and broad patterns emerging at larger scales, enabling evaluation of emergent properties and extrapolation to the flux footprint and beyond. Proper analysis of the sampling scale requires an awareness of sampling context that is often essential to the proper interpretation of optical signals. Additionally, the concept of optical types, vegetation exhibiting contrasting optical behavior in time and space, is explored as a way to frame our understanding of the controls on surface–atmosphere fluxes. Complementary normalized difference vegetation index (NDVI) and PRI patterns across ecosystems are offered as an example of this hypothesis, with the LUE model and light-response curve providing an integrating framework. I conclude that experimental approaches allowing systematic exploration of plant optical behavior in the context of the flux tower network provides a unique way to improve our understanding of environmental constraints and ecophysiological function. In addition to an enhanced mechanistic understanding of ecosystem processes, this integration of remote sensing with flux measurements offers many rich opportunities for upscaling, satellite validation, and informing practical management objectives ranging from assessing ecosystem health and productivity to quantifying biospheric carbon sequestration.

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Optical sampling expands our understanding of the "breathing" of terrestrial ecosystems beyond what is possible by eddy covariance alone. The light-use efficiency (LUE) model provides a useful conceptual framework for integrating optical and CO2 flux measurements. Contrasting optical and flux behavior can reveal distinct optical types that provide key information on flux controls. Practical applications include assessment of ecosystem health, productivity, and biospheric carbon sequestration.
Optical sampling expands our understanding of the "breathing" of terrestrial ecosystems beyond...
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