Evaluating the effect of stand properties and site conditions on the forest reflectance from Sentinel-2 time series

Abstract

Forest stand reflectance at the canopy level results from various factors, such as vegetation chemical properties, leaf morphology, canopy structure, and tree sizes. These factors are dependent on the species, age, and health statuses of trees, as well as the site conditions. Sentinel-2 imagery with the high spatial, spectral, and temporal resolution, has enabled analysis of the relationships between vegetation properties and their spectral responses at large spatial scales. A comprehensive study of these relationships is needed to understand the drivers of vegetation spectral patterns and is essential from the point of view of remote sensing data interpretation. Our study aimed to quantify the site and forest parameters affecting forest stands reflectance. The analysis was conducted for common beech-, silver fir- and Scots pine-dominated stands in a mountainous area of the Polish Carpathians. The effect of stands and site properties on reflectance in different parts of the growing season was captured using the dense time series provided by Sentinel-2 from 2018–2019. The results indicate that the reflectance of common beech stands is mainly influenced by elevation, particularly during spring and autumn. Other factors influencing beech stand reflectance include the share of the broadleaved understory, aspect, and, during summer, the age of stands. The reflectance of coniferous species, i.e., Scots pine and silver fir, is mainly influenced by the age and stand properties, namely the crown closure and stand density. The age is a primary driver for silver fir stands reflectance changes, while the stand properties have a large impact on Scots pine stands reflectance. Also, the understory influences Scots pine stands reflectance, while there appears to be no impact on silver fir stands. The influence of the abovementioned factors is highly diverse, depending on the used band and time of the season.

Forest Habitat Mapping in Natura2000 Regions in Cyprus Using Sentinel-1, Sentinel-2 and Topographical Features

“…This leads to changes in the tree's reflectance across the different parts of the wavelength. Furthermore, the reflectance might also be influenced by understory vegetation [106] because the understory vegetation might present a different spectral response than the canopy leaves [107]. Therefore, it is essential to identify the month the classifier achieves its highest performance.…”

Interplay Between Canopy Structure and Topography and Its Impacts on Seasonal Variations in Surface Reflectance in the Boreal Region of Alaska – Implication for Surface Radiation Budget

“…Forest canopy reflectance is a function of variety of factors including leaf optical properties, canopy structures, background reflectance, solar illumination geometries, and the viewing angles as well as the topography, e.g., elevation (Goel, 1988;Williams, 1991;Ni et al, 1999;Chen et al, 2000;Kötz et al, 2004;Grabska and Socha, 2021). The presence of snow on the ground or on the leaves and branches adds complexity to forest canopy reflectance because snow has very high reflective characteristics of incoming solar radiation, especially in the visible and near infrared wavelengths (Ni and Woodcock, 1999;Heinilä et al, 2019).…”