Detection of Shoot Beetle Stress on Yunnan Pine Forest Using a Coupled LIBERTY2-INFORM Simulation

Abstract

Yunnan pine shoot beetles (PSB), Tomicus yunnanensis and Tomicus minor have spread through southwestern China in the last five years, leading to millions of hectares of forest being damaged. Thus, there is an urgent need to develop an effective approach for accurate early warning and damage assessment of PSB outbreaks. Remote sensing is one of the most efficient methods for this purpose. Despite many studies existing on the mountain pine beetle (MPB), very little work has been undertaken on assessing PSB stress using remote sensing. The objective of this paper was to develop a spectral linear mixing model aided by radiative transfer (RT) and a new Yellow Index (YI) to simulate the reflectance of heterogeneous canopies containing damaged needles and quantitatively inverse their PSB stress. The YI, the fraction of dead needles, is a physically-explicit stress indicator that represents the plot shoots damage ratio (plot SDR). The major steps of this methods include: (1) LIBERTY2 was developed to simulate the reflectance of damaged needles using YI to linearly mix the green needle spectra with the dead needle spectra; (2) LIBERTY2 was coupled with the INFORM model to scale the needle spectra to the canopy scale; and (3) a look-up table (LUT) was created against Sentinel 2 (S2) imagery and inversed leaf chlorophyll content (LCC), green leaf area index (LAI) and plot SDR. The results show that (1) LIBERTY2 effectively simulated the reflectance spectral values on infested needles (mean relative error (MRE) = 1.4-18%), and the YI can indicate the degrees of needles damage; (2) the coupled LIBERTY2-INFORM model is suitable to estimate LAI (R 2 = 0.73, RMSE = 0.17 m m −2 , NRMSE = 11.41% and the index of agreement (IOA) = 0.92) and LCC (R 2 = 0.49, RMSE = 56.24 mg m −2 , NRMSE = 25.22% and IOA = 0.72), and is better than the original LIBERTY model (LAI: R 2 = 0.38, RMSE = 0.43 m m −2 , NRMSE = 28.85% and IOA = 0.68; LCC: R 2 = 0.34, RMSE = 76.44 mg m −2 , NRMSE = 34.23% and IOA = 0.57); and (3) the inversed YI is positively correlated with the measured plot SDR (R 2 = 0.40, RMSE = 0.15). We conclude that the LIBERTY2 model improved the reflectance simulation accuracy of both the needles and canopies, making it suitable for assessing PSB stress. The YI has the potential to assess PSB damage.

The Impact of NPV on the Spectral Parameters in the Yellow-Edge, Red-Edge and NIR Shoulder Wavelength Regions in Grasslands

“…One was the impact of dead material on in situ measurement of LAI, and a second was the influence of dead material on spectral parameters and NDVI. Plant canopy measuring devices (e.g., Li-cor LAI-2000 and Li-cor LAI-2200 plant canopy analyzer), capturing solar radiation intercepted by the vegetation canopy, are the most popular field method for LAI measurement [53][54][55]. However, research has found that dead materials (i.e., standing dead materials without litter) also contributes to LAI measured by the plant canopy devices, albeit with a smaller contribution than green vegetation [25,56].…”

Detection of Pine Shoot Beetle (PSB) Stress on Pine Forests at Individual Tree Level using UAV-Based Hyperspectral Imagery and Lidar

“…In each plot, tree variables including tree height (H), crown base height (CBH), diameter at breast height (DBH), crown diameter (CD), and SDR were measured. The SDR was defined as the proportion of damaged shoots number to total shoots number for each tree crown [5,26]. Each SDR was between 0% and 100%.…”

“…We divided tree damage degrees into five levels: healthy tree (SDR: 0-10%), slightly infected tree (SDR: 10-30%), moderately infected tree (SDR: 30-50%), severely infected tree (SDR: 50-80%), and dead tree (SDR: 80-100%). Moreover, the biochemical parameters such as the leaf chlorophyll content (Cab) of single trees were derived by averaging four level shoots Cab using a calibrated CCM-300 Chlorophyll Content Meter [26]. Summary statistics of two plots are given in Table 1.…”

Retrieving the Infected Area of Pine Wilt Disease-Disturbed Pine Forests from Medium-Resolution Satellite Images Using the Stochastic Radiative Transfer Theory

“…Some studies have utilized radiative transfer models to detect forest pest and diseases using simulations. For example, leaf incorporating biochemistry exhibiting reflectance and transmittance yields (LIBERTY)-a leaf model-and invertible forest reflectance model (INFORM)-a canopy model-were coupled to detect pine shoot beetle (PSB) stress in Yunnan Pine forest [30]. One-dimensional (1D) radiative transfer (RT) models are not qualified enough to accurately retrieve the damage level of PSB damage [31], the three-dimensional (3D) Radiosity Applicable to Porous IndiviDual Objects (RAPID) model was used to estimate PSB damage.…”