The fraction of absorbed photosynthetically active radiation (FAPAR) defines the fraction of photosynthetically active radiation (PAR) absorbed by the green parts of the canopy, and thus expresses the canopy’s energy absorption capacity. FAPAR has been recognized by Global Climate Observing System (GCOS) as one of the fundamental terrestrial state variables in the context of the climate change.
Dependent on the elements such as solar zenith angle, FAPAR shows obvious variations during a day. It is a key variable in models assessing vegetation health, gross ecosystem production and so on. However, there is limited research regarding RS-based FAPAR data on regional scale.
Dr. ZHANG Yinghui and Prof. FANG Hongliang at the Institute of Geographic Sciences and Natural Resources Research (IGSNRR) proposed a new method to estimate the intra-daily variations of the FAPARs from the geostationary Himawari-8 satellite data. Field campaigns over paddy rice fields in northeastern China were conducted to validate the estimated results.
The results showed that the instantaneous total and direct FAPAR values show a “bowl-shaped” pattern in clear days, while the diffuse FAPAR remains stable before 16:00 local solar time. The FAPAR values decrease in the late afternoon (16:00 – 18:00). The instantaneous FAPAR at 10:00–10:30 underestimates the daily FAPAR in the paddy rice area, while the instantaneous FAPAR at 9:30 or 14:30 can be used to represent the daily FAPAR.
They also found that the FAPAR products provided by the European GEOV2 program overestimate those by the United States MODIS program. All current geostationary satellite data could be combined to generate the instantaneous and daily FAPAR products for global vegetation modeling studies.
This study was supported by the National Key Research and Development Program of China. It has been published in a recent issue of Agricultural and forest meteorology.
Zhang, Y., Fang, H., Wang, Y., Li, S., (2021). Variation of intra-daily instantaneous FAPAR estimated from the geostationary Himawari-8 AHI data. Agricultural and Forest Meteorology, 307, 108535. https://doi.org/10.1016/j.agrformet.2021.108535.
Paddy Rice Experiment in the Sanjiang Plain (PRESP 2019) Field Measurement Report: