Digital Aerial Photogrammetry (DAP) and Airborne Laser Scanning (ALS) as Sources of Information about Tree Height: Comparisons of the Accuracy of Remote Sensing Methods for Tree Height Estimation

Abstract

The rapid developments in the field of digital aerial photogrammetry (DAP) in recent years have increased interest in the application of DAP data for extracting three-dimensional (3D) models of forest canopies. This technology, however, still requires further investigation to confirm its reliability in estimating forest attributes in complex forest conditions. The main purpose of this study was to evaluate the accuracy of tree height estimation based on a crown height model (CHM) generated from the difference between a DAP-derived digital surface model (DSM) and an airborne laser scanning (ALS)-derived digital terrain model (DTM). The tree heights determined based on the DAP-CHM were compared with ground-based measurements and heights obtained using ALS data only (ALS-CHM). Moreover, tree- and stand-related factors were examined to evaluate the potential influence on the obtained discrepancies between ALS- and DAP-derived heights. The obtained results indicate that the differences between the means of field-measured heights and DAP-derived heights were statistically significant. The root mean square error (RMSE) calculated in the comparison of field heights and DAP-derived heights was 1.68 m (7.34%). The results obtained for the CHM generated using only ALS data produced slightly lower errors, with RMSE = 1.25 m (5.46%) on average. Both ALS and DAP displayed the tendency to underestimate tree heights compared to those measured in the field; however, DAP produced a higher bias (1.26 m) than ALS (0.88 m). Nevertheless, DAP heights were highly correlated with the heights measured in the field (R2 = 0.95) and ALS-derived heights (R2 = 0.97). Tree species and height difference (the difference between the reference tree height and mean tree height in a sample plot) had the greatest influence on the differences between ALS- and DAP-derived heights. Our study confirms that a CHM computed based on the difference between a DAP-derived DSM and an ALS-derived DTM can be successfully used to measure the height of trees in the upper canopy layer.

UAV Based Estimation of Forest Leaf Area Index (LAI) through Oblique Photogrammetry

“…Our research result was that coupling oblique photos and nadir photos can effectively improve the vertical coordinate accuracy of the point cloud. However, it is worth noting that under the premise of not using GCP, the height coordinate error provided by the scheme with nadir-photos-only reached 10.8 m (Figure 11), which is quite different from the results of other researchers [35][36][37]. The specific reason for this result is not clear, but it may be related to the camera calibration result or ground type, which can be further explored in future research.…”

Comparison of Coniferous Plantation Heights Using Unmanned Aerial Vehicle (UAV) Laser Scanning and Stereo Photogrammetry

“…A variety of comparable studies on the performance of LiDAR and USP point clouds for forest attribute parameters have been conducted [16] including diverse forest environments such as complex boreal forest types, complex coastal forest [18], and subtropical planted forests [19]. Most studies have concluded that LiDAR provides higher accuracy for modeling and predicting forest attributes than stereo photogrammetry data [20][21][22]. However, few studies have analyzed the performance of USP on temperate coniferous plantations in mountainous area.…”

Suitability of Aerial Photogrammetry for Dump Documentation and Volume Determination in Large Areas

“…The most common products of aerial image processing are vector maps, orthophoto maps, digital terrain models (DTM), and digital surface models (DSM) [20][21][22]. In recent years, digital aerial cameras and appropriate software development have provided sensors with higher resolution, allowing the Earth's surface to be captured with detail-level improvement at the same flight height, respectively reducing the necessary number of images and thus flight time and cost of imaging [23]. The minimizing of fieldwork time, rapidity of photogrammetric data collection and processing, and high detail and accuracy of the terrain models generated by modern software currently take aerial photogrammetry forward as an exciting alternative in terms of quality and efficiency in comparison with terrestrial geodetic methods [24].…”

“…Therefore, from the available methods for performing the required measurements, the method of aerial photogrammetry has been chosen as likely the most appropriate way to fulfil the purpose of measurement. The advantages of this method consist of the very short time for measurement, fast and automated data processing procedures, sufficient precision, the non-contact method of measuring, and the minimized working time in the factory [3,18,23].…”