remote sensing Article A Comparison of Stand-Level Volume Estimates from Image-Based Canopy Height Models of Different Spatial Resolutions Ivan Balenovi´c 1,*, Anita Simic Milas 2 and Hrvoje Marjanovi´c 1 1 Division for Forest Management and Forestry Economics, Croatian Forest Research Institute, Trnjanska Cesta 35, Zagreb HR-10000, Croatia;
[email protected] 2 School of Earth, Environment and Society, Bowling Green State University, 190 Overman Hall, Bowling Green, OH 43403, USA;
[email protected] * Correspondence:
[email protected]; Tel.: +385-1-63-11-584 Academic Editors: Guangxing Wang, Erkki Tomppo, Dengsheng Lu, Huaiqing Zhang, Qi Chen, Lars T. Waser, Randolph H. Wynne and Prasad S. Thenkabail Received: 8 December 2016; Accepted: 12 March 2017; Published: 15 March 2017 Abstract: Digital aerial photogrammetry has recently attracted great attention in forest inventory studies, particularly in countries where airborne laser scanning (ALS) technology is not available. Further research, however, is required to prove its practical applicability in deriving three-dimensional (3D) point clouds and canopy surface and height models (CSMs and CHMs, respectively) over different forest types. The primary aim of this study is to investigate the applicability of image-based CHMs at different spatial resolutions (1 m, 2 m, 5 m) for use in stand-level forest inventory, with a special focus on estimation of stand-level merchantable volume of even-aged pedunculate oak (Quercus robur L.) forests. CHMs are generated by subtracting digital terrain models (DTMs), derived from the national digital terrain database, from corresponding digital surface models (DSMs), derived by the process of image matching of digital aerial images.