UAV-based method for measuring CO 2 emissions in forest ecosystems

This study addresses the difficulty of accurately quantifying CO2 emissions in forest ecosystems due to spatial heterogeneity, complex terrain, and the combined effects of horizontal and vertical transport. A UAV-based platform, capable of three-dimensional CO2 emission observation, was developed, evaluated and applied to a forest ecosystem. The system integrates a high-precision closed-path CO2 analyzer with a calibrated ultrasonic anemometer, and employs complementary box-pattern and profile-pattern flight strategies within a mass-balance framework to simultaneously resolve horizontal transport and vertical exchange. Validation against a long-term eddy-covariance (EC) flux tower shows that vertical CO2 fluxes derived using the gradient method agree well with EC observations across seasons (R² ≈ 0.76–0.77). Box-pattern flights further reveal pronounced diurnal variation: lateral advection dominates in the early morning, whereas vertical uptake prevails under well-mixed midday conditions. Sensitivity analyses across scales of 50 m, 100 m, 150 m indicate that CO2 emission intensity is sensitive to control-volume dimensions and shows spatial heterogeneity above the forest. Uncertainty assessment suggests that the total relative uncertainty of UAV-derived emissions is typically ~15 %, with wind-field calibration as the main error source. Overall, this UAV approach provides a flexible and reliable complement for analyzing near-surface three-dimensional CO2 transport over complex and heterogeneous forests, helping to overcome the limited spatial coverage of traditional flux towers and remote sensing.