NDVI and Fluorescence Indicators of Seasonal and Structural Changes in a Tropical Forest Succession

Abstract

In this research, the Sun-induced Chlorophyll Fluorescence (SIF) signal was derived from field-based spectrometers and Hyperion satellite imagery of Hong Kong's Country Parks by applying the Fraunhofer Line Difference (FLD) method. Due to high levels of atmospheric aerosols and water vapour in the study area, a modified FLD method (FLD-M) was tested for its ability to deliver improved SIF estimates by cancelling out the effects of atmospheric scattering. The SIF results were compared with the Normalised Difference Vegetation Index (NDVI), and analysed according to seasonality, five successional age groups of forest and monoculture exotic plantations. Results indicate that SIF methods are more sensitive to seasonal phenology and diurnal fluctuations than the NDVI, indicating its greater sensitivity to photosynthetic activity. The SIF responds earlier and stronger, to senescence in winter and green-up in summer. Field spectrometer data showed NDVI to be unresponsive to time of day, whereas fluorescence responds to changes in sunlight intensity from 10:15 am to 02:00 pm. Both seasonal and diurnal results indicate that SIF is better than NDVI in representing the subtle changes in vegetation conditions. Although both NDVI and SIF distinguish between the four woody structural stages of vegetation, only SIF can distinguish between forest and exotic plantations, the difference being greater in the dry season. The study provides an improved operational remote sensing methodology for investigating the health status of tropical secondary forest, where atmospheric turbidity is high.

Solar-induced fluorescence products show variable skill in constraining global patterns in biospheric CO2 fluxes

“…These include observations from aircraft or tall towers, as in Alden et al (2016), and/or geostationary satellites like the Geostationary Carbon Cycle Observatory (GeoCarb). Such observations could help bridge the gap between site-level evaluation (e.g., Irteza et al, 2021;Doughty et al, 2019) and global-scale efforts like the present study.…”

Solar‐Induced Fluorescence Helps Constrain Global Patterns in Net Biosphere Exchange, as Estimated Using Atmospheric CO2 Observations

“…(2016). Such observations could help bridge the gap between site‐level evaluation (e.g., Doughty et al., 2019; Irteza et al., 2021; C. Wang et al., 2019) and efforts to quantify regional‐scale relationships between SIF, GPP, and NBE.…”

“…These include observations from aircraft or tall towers, as in Alden et al (2016). Such observations could help bridge the gap between site-level evaluation (e.g., Doughty et al, 2019;Irteza et al, 2021; and efforts to quantify regional-scale relationships between SIF, GPP, and NBE.…”

Approaches of Satellite Remote Sensing for the Assessment of Above-Ground Biomass across Tropical Forests: Pan-tropical to National Scales

“…Both the studies [125,126] documented the utility of NDVI in determining the age classes of secondary forests. A recent study documented a significant difference in fluorescence emissions (which is a proxy variable for plant biomass or carbon flux measurement) among different age groups of Hong Kong's recovering tropical forests [127]. They observed higher productivity up to the age of 61 years old and then a decline in productivity in the old-growth forests.…”