Retrieval of the Overstory and Understory Leaf Area Index of Forest Stands Using a Model of Forest Canopy Reflectance

In this paper, the Kuusk-Nilson forest reflectance and transmittance (FRT) model was inverted to retrieve the overstory and understory leaf area index (LAI) of forest stands in the Longmenhe Nature Reserve (Xingshan County, Hubei province, China). Atmospherically and topographically corrected hyperspectral Hyperion imagery and field data had been input to retrieve the overstory and understory LAI simultaneously using FRT inverted model. An uncertainty and sensitivity matrix was used to analyze the sensitivity of the FRT model parameters based on field data. Twenty-one Hyperion bands were selected based on principal-components analysis and band importance from total Hyperion bands. Eight different Hyperion band combinations from 21 Hyperion bands were tested to evaluate the accuracy of the inversion of overstory and understory LAI. Our study showed that the overstory LAI of stands can be better retrieved when considering the understory LAI compared to only use total LAI.