http://hdl.handle.net/1807/123193

Rogers, Cheryl Anne (2022) Complementarity of Solar Induced Chlorophyll Fluorescence and the Photochemical Reflectance Index for Remote Estimation of Terrestrial Gross Primary Productivity, Tspace - Theses, http://hdl.handle.net/1807/123193

Terrestrial vegetation helps mitigate the accumulation of CO2 in the atmosphere through photosynthesis, which locks CO2 into vast stores of vegetative material. However, the rate of this flux is itself sensitive to global change and may fluctuate in ways that are difficult to predict. Monitoring gross primary productivity (GPP) continuously across both space and time is thus critical to understanding the risks of continued climate change. This thesis evaluates satellite remote sensing measures to improve assessment of carbon uptake and explores the complementarity and confounding factors of two physiologically related spectral indices: solar induced chlorophyll fluorescence (SIF), and the photochemical reflectance index (PRI).An evaluation of the impact of land cover and latitude on SIF phenology across the Province of Ontario using a GIS approach shows higher SIF magnitudes in more densely vegetated land cover types, early start of season in urban environments, and delayed start of season in croplands. Exploiting the 2017 North American Solar Eclipse as a natural shading experiment over a mixed forest canopy at proximal scale indicates that changes in PRI can result from multiple scattering of light through a forest canopy. As SIF and PRI are highly sensitive to canopy structure, I devise and test methods to measure leaf area index from understory light sensors. I report a near 20-year record of canopy structure for a mixed forest site. Finally, I report the results of a comprehensive field campaign to characterize the causes of variability in SIF, PRI and GPP across diurnal, seasonal and interannual time periods. Variability in PRI and SIF yield are associated with changes in canopy chlorophyll content and canopy structure. The findings support emerging evidence that structure and radiation dominate SIF variation and highlight limitations of PRI in tracking light stress over long time series. The findings advance our ability to assess vegetation productivity from space and indicate factors that may confound our interpretation of remotely sensed spectral indices.

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