Utility of spectral vegetation index for estimation of gross CO2 flux under varied sky conditions

摘要: Abstract To estimate the gross CO2 flux (FCO2) of deciduous coniferous forest from canopy spectral reflectance, we introduced vegetation indices (VIs) into a light use efficiency (LUE) model mature Japanese larch (Larix kaempferi) forest. We measured eddy covariance and reflectance at half-hourly intervals during one growing season, investigated relationships between parameters LUE (FAPAR, ɛ) 3 types VIs (NDVI, PRI, EVI) in both clear sky cloudy conditions. FAPAR (fraction absorbed photosynthetically active radiation) had positive linear relationship with NDVI (normalized difference index) EVI (enhanced index), condition little effect on relationships. The relative RMSE (root mean square error) APAR (absorbed based incoming PAR estimated function was less than 10.5%, irrespective condition. Half-hourly values ɛ (conversion energy) showed seasonal variation related to leaf phenology short-term intensity due varied sun position Both PRI (photochemical were significantly correlated ɛ. as result their similar variation. However, since did not detect ɛ, differed among On other hand, although could trace green needles, became non-linear drastic reduction senescent needles. EVI/(PRI/PRImin), combined index 6-day moving minimum value (PRImin), throughout seasons This allow us all conditions smaller error (rRMSE = 35.2%) using or alone (38.7%–48.7%). Consequently, this index-derived NDVI-based gave low estimation FCO2 36.4%, 8.3 μmol m− 2 s− 1). Although there are still various issues resolve, including adaptive limit combination type, conclude that increased accuracy uptake even though varied.