Practical LAI Estimation with DHP Images in Complex Forest Structure with Rugged Terrain

Abstract

Leaf area index is a key structural parameter for biological and physical processes. Korea is planning to launch CAS500-4 in 2025, so in situ data is needed to validate the leaf area index. Unlike other networks (e.g., NEON and TERN), establishing an elementary sampling unit is difficult in Korea due to the complex forest structure and rugged terrain. Therefore, pixel-level correspondence between the satellite product and fisheye footprints is the best way to verify in complex terrain. In this study, we analyzed the spatial footprint of fisheye lenses in different forest types using terrestrial LiDAR data for the first time. The three-dimensional forest structure was analyzed at various viewing zenith angles, and the footprint radius was approximately 3 m at view zenith angle (VZA) 20° and approximately 10 m at VZA 90°. We also analyzed the Z-values from terrestrial laser data and the plant area index on leafless seasons to assess the impact of obstacles, such as tree trunks, under various viewing zenith angles. The analysis showed that the influence of woody components increases dramatically as the VZA exceeds 40°. Such factors influenced the increase in LAI and the decrease in the clumping index as the VZA increased. Overall, we concluded that narrowing VZA between 20° and 40° is appropriate for Korean forests with complex structures.

Insights into Canopy Escape Ratio from Canopy Structures: Correlations Uncovered through Sentinel-2 and Field Observation

“…Forest types were identified through field surveys and classified into five categories: deciduous broadleaf forests (DBFs), deciduous needleleaf forests (DNFs), evergreen broadleaf forests (EBFs), evergreen needleleaf forests (ENFs), and mixed forests (MFs) (Table 1). Similarly, climate diversity was also considered, categorizing the climates of the sites into six distinct types-Cfa, Cwa, Dfa, Dfb, Dwa, and Dwb-according to the high-resolution Köppen Climate Classification map [29] for the period 1991-2020.…”

“…The exact dates of data collection are detailed in the last column. The Köppen Climate Classification [29] categorizes our sites into 6 groups: Cfa (Temperate, no dry season, hot summer), Cwa (Temperate, dry winter, hot summer), Dfa (Cold, no dry season, hot summer), Dfb (Cold, no dry season, warm summer), Dwa (Cold, dry winter, hot summer), and Dwb (Cold, dry winter, warm summer). The forest types across our sites were identified as deciduous broadleaf forests (DBFs), deciduous needleleaf forests (DNFs), evergreen broadleaf forests (EBFs), evergreen needleleaf forests (ENFs), and mixed forests (MFs).…”