Three-dimensional forest stand height map production utilizing airborne laser scanning dense point clouds and precise quality evaluation

In remote sensing, estimation of the forest stand height is an ever-challenging issue due to the difficulties encountered during the acquisition of data under forest canopies. Stereo optical imaging offers high spatial and spectral resolution; however, the optical correlation is lower in dense forests than in open areas due to an insufficient number of matching points. Therefore, in most cases height information may be missing or faulty. With their long wavelengths of 0.2 to 1.3 m, P-band and L-band synthetic aperture radars are capable of penetrating forest canopies, but their low spatial resolutions restrict the use of single-tree based forest applications. In this study, airborne laser scanning was used as an effective remote sensing technique to produce large-scale maps of forest stand height. This technique produces very high-resolution point clouds and has a high penetration capability that allows for the detection of multiple echoes per laser pulse. A study area with a forest coverage of approximately 60\% was selected in Houston, USA, and a three-dimensional color-coded map of forest stands was produced using a normalized digital surface model technique. Rather than being limited to the number of ground control points, the accuracy of the produced map was assessed with a model-to-model approach using terrestrial laser scanning. In the accuracy assessment, the standard deviation was used as the main accuracy indicator in addition to the root mean square error and normalized median absolute deviation. The absolute geo-location accuracy of the generated map was found to be better than 1 cm horizontally and approximately 40 cm in height. Furthermore, the effects of bias and relative standard deviations were determined. The problems encountered during the production of the map, as well as recommended solutions, are also discussed in this paper

Geometric evaluation, automated DEM and orthoimage generation from along-track stereo ASTER images

2nd International Conference on Recent Advances in Space Technologies -- JUN 09-11, 2005 -- Istanbul, TURKEYWOS: 000233198100098A cloud-free ASTER scene combination covering 61.5km x 63km Zonguldak testfield in the north-west Turkey has been analysed. It comprises the nadir and backward views with a base-to-height ratio of 0.6. The pixel size on the ground is 15m. The bundle orientation was executed with the related module of PCI Geomatica V9.1.4 software package and resulted the 3D geo-positioning to an accuracy of about 14m in planimetry and 13m in height. This level of accuracy can be provided using the number of GCPs up to 14 which are distributed over the scene uniformly. Based on the scene orientation, a DEM of the area has been determined by an automatic image matching and PCI system yielded a DEM with 30m cell size. For the validation of extracted DEM, different groups of GCPs selected over the testfield were utilized. In this analysis, GCPs were located in the raster DEM in according to their planimetric coordinates, then the heights are estimated by the bilinear interpolation of the neighboured grid cells. This was done by the program DEMINT and mean square differences was obtained in the range of 12 to 14m. Moreover., matched DEM was checked against reference DEM based on digitised contour lines from the 1:25000 scale topographic maps using program DEMANAL. The discrepancies between the two DEMs were determined as reference DEM minus matched DEM. Then positive biases resulted which show that matched DEM occurred under the reference DEM. These biases appeared also in the superimposition of contours from two DEMs. Image of DZ discrepancies is dispayed as a function of grey values as well and highest residuals occurred mainly at the ridges. In the meantime, RMSE-Z from the comparison of both DEMs obtained very close in the range of +/- 21-22m. Finally, orthoimage was generated using matched DEM and nadir image component of ASTER stereopair without problem. Planimetric accuracy check of this product was realized using the GCPs and shows no systematic error pattern overall.IEEE, AIAA, isprs, Turkish AF Acad, Istanbul Tech Univ, Bogazici Univ, Marmara Uni