The influence of window size on remote sensing-based prediction of forest structural variables

Abstract

Background Determining the appropriate window size is a critical step in the estimation process of stand structural variables based on remote sensing data. Because the value of the reference laser and image metrics that affect the quality of the prediction model depends on window size. However, suitable window sizes are usually determined by trial and error. There are a limited number of published studies evaluating appropriate window sizes for different remote sensing data. This research investigated the effect of window size on predicting forest structural variables using airborne LiDAR data, digital aerial image and WorldView-3 satellite image. Results In the WorldView-3 and digital aerial image, significant differences were observed in the prediction accuracies of the structural variables according to different window sizes. For the estimation based on WorldView-3 in black pine stands, the optimal window sizes for stem number (N), volume (V), basal area (BA) and mean height (H) were determined as 1000 m(2), 100 m(2), 100 m(2) and 600 m(2), respectively. In oak stands, the R-2 values of each moving window size were almost identical for N and BA. The optimal window size was 400 m(2) for V and 600 m(2) for H. For the estimation based on aerial image in black pine stands, the 800 m(2) window size was optimal for N and H, the 600 m(2) window size was optimal for V and the 1000 m(2) window size was optimal for BA. In the oak stands, the optimal window sizes for N, V, BA and H were determined as 1000 m(2), 100 m(2), 100 m(2) and 600 m(2), respectively. The optimal window sizes may need to be scaled up or down to match the stand canopy components. In the LiDAR data, the R-2 values of each window size were almost identical for all variables of the black pine and the oak stands. Conclusion This study illustrated that the window size has an effect on the prediction accuracy in estimating forest structural variables based on remote sensing data. Moreover, the results showed that the optimal window size for forest structural variables varies according to remote sensing data and tree species composition.