Net Fluxes of Broadband Shortwave and Photosynthetically Active Radiation Complement NDVI and Near Infrared Reflectance of Vegetation to Explain Gross Photosynthesis Variability Across Ecosystems and Climate

Authors

Kanishka Mallick, Luxembourg Institute of Science and Technology
Joseph Verfaillie, University of California, Berkeley
Tianxin Wang, University of California, Berkeley
Ariane Arias Ortiz, University of California, Berkeley
Daphne Szutu, University of California, Berkeley
Koong Yi, University of California, Berkeley
Yanghui Kang, University of California, Berkeley
Robert Shortt, University of California, Berkeley
Tian Hu, Luxembourg Institute of Science and Technology
Mauro Sulis, Luxembourg Institute of Science and Technology
Zoltan Szantoi, European Space Agency
Gilles Boulet, Centre d'Etudes Spatiales de la Biosphère
Joshua B. Fisher, Chapman UniversityFollow
Dennis Baldocchi, University of California, Berkeley

Document Type

Article

Publication Date

4-26-2024

Abstract

A significant challenge in global change research is understanding how vegetation interacts with the environment to influence ecosystem gross primary productivity (GPP) through carbon assimilation. One emerging objective is to consistently predict GPP fluctuations worldwide by establishing a robust scaling relationship between GPP measured at flux towers and satellite spectral reflectance data. However, a major hurdle in achieving this goal is the discrepancy in spatial resolution between early satellite measurements and eddy flux measurements. By using a large set of growing season data covering 100 site-years in North and Central America, we explored the potential of transforming incident and reflected shortwave (R_g) and photosynthetically active radiation (PAR) measurements into a broadband normalized difference vegetation index (NDVI) and near-infrared (NIR) reflectance of vegetation (NIRv) which simultaneously explains the GPP variability. We found that the broadband NDVI and NIRv derived from R_g and PAR measurements at the daily time scale were highly correlated with Planet Fusion, Landsat-8/9, and Sentinel-2 narrowband NDVI and NIRv across a wide range of climate and ecological gradients. The differences between satellite and broadband NDVI and NIRv were found to be significantly associated with soil background variations, phenological stages, water stress and signal saturation of broadband NIR reflectance at high biomass. The seasonal variability of broadband NDVI and NIRv remarkably captured the seasonality of vegetation phenology, evaporative fraction, GPP and rainfall in different ecosystems. Although saturation of GPP at high NDVI was evident, a linear relationship between broadband NIRv times incident PAR versus GPP indicated the effectiveness of NIRv-based approach to capture the hidden light use efficiency impacts on GPP. Our study concludes that inexpensive measurement of R_g and PAR components can provide reliable information on NDVI, NIRv, and GPP uninterruptedly. This enhances the sensing capability of flux tower sites without requiring additional spectrometer measurements. The proposed in-situ vegetation indices make a compelling case on using radiation signals for handshaking between ecosystem-scale measurements and remote sensing observables relevant to carbon uptake.

Comments

NOTICE: this is the author’s version of a work that was accepted for publication in Remote Sensing of Environment. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Remote Sensing of Environment, volume 307, in 2024. https://doi.org/10.1016/j.rse.2024.114123

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Recommended Citation

Mallick, K., Verfaillie, J., Wang, T., Ortiz, A.A., Szutu, D., Yi, K., Kang, Y., Shortt, R., Hu, T., Sulis, M., Szantoi, Z., Boulet, G., Fisher, J.B., Baldocchi, D. 2024. Net fluxes of broadband shortwave and photosynthetically active radiation complement NDVI and near infrared reflectance of vegetation to explain gross photosynthesis variability across ecosystems and climate. Remote Sensing of Environment, 307, 114123. https://doi.org/10.1016/j.rse.2024.114123

Copyright

Elsevier

Creative Commons License

This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.