Study On Digital Photography Surveying Technology Of Individual Tree Parameters

The current investigation of forest resources is mainly to use aerial photographs to obtain the data by computer and digital measurement. Based on aerial photographs of Dai Ling Liang Shui National Nature Reserve in Yichun in Sep.2008 and the theory of automatic triangulation, we used VirtuoZo AAT of VirtuoZo NT system to build stereo pairs. Mapping module of VirtuoZo GIS was used to measure east-west and north-south crown ranges and height of trees in survey region on the basis of stereo pairs. In order to improve the measurement accuracy, the following aspects were considered in this study. Firstly, we considered image errors mainly caused by camera lens distortion, atmospheric refraction error and the effects of earth curvature on coordinates of image points, and image-shift due to camera tilt and topographic inequality. We avoided or reduced the various errors of aerial photos by correcting aerial photos. Secondly, we considered synthetically aerial photo appearances, topographical features, species distribution and other factors combined of direct visual interpretation method and indirect visual interpretation method. In order to eliminate or reduce the errors caused by environmental factors. The measuring accuracy was high which could be seen from the results.The main conclusions of this study are as follows:(1) Aerial photos are utilized reasonably and scientifically for Forest Inventory which can greatly alleviate some issues, such as arduous tasks, tough working conditions, long working hours, costly research and so on.(2) The measurements of aerial photo triangulation of aerial photographs by digital photogrammetry software-VirtuoZo NT have practical values for Forest Inventory on the basis of aerial photos in China.(3) Compared with traditional word mode of air photogrammetry, the application of GPS-supported digital aerial triangulation greatly reduces the difficulty of aerial operations and shorts the cycle of aerial mapping.(4) On the basis of the elements of exterior orientation of aerial photos and Aerial Triangulation Encryption Principle, the measurements of tree heights and crown diameters are speed and high precision. The No.32 permanent plot of No.18 stand of No.17 forest compartment in Dai Ling Liang Shui National Nature Reserve in Yichun is as an example. Road-test data compare with enciphered data, the coefficient of correlation of tree height is 0.897 and the coefficients of correlation of east-west/south-north crown are all 0.909. They are all reach the demands of Forest Inventory.