Work

Effect of Albedo Footprint Size on Relationships between Measured Albedo and Forest Attributes for Small Forest Plots

Year: 2024

Type: article

Abstract: Albedo of boreal forests depends on properties of the forests and is a key parameter for understanding the climate impact of forest management practices at high northern latitudes. While high-resolution albedo retrievals from satellites remain challenging, unmanned aerial vehicles (UAVs) offer the ability to obtain albedo corresponding to the typical size of forest stands or even smaller areas, such as forest plots. Plots and pixels of sizes in the typical range of 200–400 m2 are used as basic units in forest mapping supporting operational management in the Nordic countries. In this study, the aim was to evaluate the effect of differences in footprint size of measured albedo and fixed-area forest plots on the relationship between albedo and forest attributes. This was done by examining the correlation between albedo and field-measured forest attributes and metrics derived from airborne laser scanner data using linear regression models. Albedo was measured by UAV above 400‑m2, circular forest plots (n=128) for seven different flight heights above the top of the canopy. The flight heights were chosen so the plots were always smaller than the footprint of measured albedo, and the area of a forest plot constituted 30–90% of the measured albedo. The applied pyranometer aboard the UAV measured the albedo according to a cosine response across the footprint. We found strongest correlation when the albedo footprint was most similar to the plots in size, i.e., when the plots constituted 80–90% of the measured albedo. Measured albedo of plots in both regeneration forests and mature forests were highly sensitive (p-values ≤0.001) to the footprint size, with a mean albedo difference of 11% between the smallest and largest footprints. For mature forests, the correlation between field-measured forest attributes and albedo was similar for different footprint sizes of measured albedo if species-specific information was excluded in the modelling. The study demonstrates the importance of similar spatial scales of the albedo measurements and the forest plot subject to measurements.

Source: Remote Sensing

DOI: 10.3390/rs16163085

Authors: Eirik Næsset Ramtvedt, Hans Ole Ørka, Ole Martin Bollandsås, Erik Næsset, Terje Gobakken

Institution: Norwegian University of Life Sciences

Language: English

Topic: Remote Sensing and LiDAR Applications

Subfield: Environmental Engineering

Field: Environmental Science

Domain: Physical Sciences

SDGs: Life on land, Climate action

Open Access status: gold

Estimated APC paid: $3,069