| ABSTRACTIn this paper, tridimensional green biomass of urban six districts(Xicheng, Dongcheng, Haidian, Chaoyang, Shijingshan and Fengtai) of Beijing has been estimated and analyzed. Different from the conventional method that proper volume formula is selected according to the crown shape, single tree scanning by terrestrial three dimensional laser scanning system has been used, and peripheral point cloud data of crown was used to calculate the volume and obtained tridimensional green biomass of single tree.Combined with the RS and GIS technology, the three dimensional green biomass inversion model has been established with the help of mathematical statistics knowledge. The three dimensional green biomass of urban six districts was got and analyzed. In addition, suggestions have been proposed to provide the scientific basis for urban green land planning.Based on the terrestrial laser scanning system, conifers and broad-leaved trees of urban six districts of Beijing have been scanned plant by plant, to acquire tridimentional green biomass per plant. SPOT5 remote sensing was used as the data source, the three-dimensional green biomass model has been established with the help of multivariate statistical software SPSS and remote sensing and geographic information systems model and spatial analysis tool. The three-dimensional green biomass of forest in urban six districts of Beijing was estimated and the correlation analysis has been done, in order to quickly and accurately estimate three dimensional green biomass of urban six districts of Beijing, providing an effective means and methods. The following conclusions have been got:(1) Through systematic sampling and typical sampling, selecting several greening places such as campus,parks,sidewalks,residential districts,parking lots etc, in these places, terrestrial laser scanner FARO LS880 was used to scan over 30 tree species plant by plant, like arborvitae, cedar, pine, cypress, ginkgo, poplar, sycamore, willow tree, Sophora japonica, Ailanthus altissima, Koelreuteria, ash, maple, cork oak and other nearly ten common tree species in Beijing, and a total of more than 1,000 trees have been scanned. By using FARO SCENE point cloud processing software, single plants were extracted of plant crown point cloud, and in the reverse engineering software Geomagic, the factors like height, diameter, crown width, branch were measured plant by plant; By reading through the programming, relative three-dimensional coordinates of the point cloud concerning the crown of each plant were measured and then the outermost point of the surface formed by the irregular surface area of direction perpendicular to the trunk was calculated, and then along the direction of trunk, the infinitesimal method was used to cut a round table volume, and finally they were added together to acquire the crown volume, that is the tridimentional green biomass of crown upper;(2)The image of SPOT5 with the spatial resolution of 2.5m panchromatic band and an empty spatial resolution of 10m multispectral remote sensing data has been selected, combined with Worldview and Google earth and auxiliary data like topographic maps etc, and then combination of supervised classification and visual interpretation methods has been used to do classification and extraction of the vegetation in the urban six districts of Beijing. In this paper,6 land types have been classified:coniferous forest, broadleaf forest, grassland, farmland, water, construction sites and other lands, and the overall classification accuracy reached 83%. Verified by field survey points, conformity was over 93%; According to the scanning data of tree species, remote sensing and GIS information, multivariate statistical analysis methods was used for variable selection, and then three dimensional green biomass models of coniferous and broadleaf trees have been established. The coniferous trees three-dimensional green biomass model is:V=1.149-0.096B1-0.1B2+0.199SWIR, and broadleaf trees three-dimensional green biomass model is: V=-40.290-0.236B1-0.188B2+0.487SWIR. with the correlation coefficient of models were 0.946 and 0.893 respectively, and the significance was shown as highly significant. Through regression standard residual and cumulative probability distribution, the regression of model was good, and the test sample data was used for accuracy estimation under the regression estimates in 0.05 and 0.01 confidence level. The results showed that the accuracy coniferous trees were 96.85% and 95.84%, and the accuracy of broad-leaved trees were 89.29% and 85.84%. Therefore, it can be drawn that the tridimensional green biomass established by the above method can be used.(3) The three-dimensional green biomass model has been used to estimate the green biomass of urban six districts of Beijing. By analysis, the total amount of green biomass concerning urban six districts of Beijing is 399,129,501.69 m3. Haidian District owns the largest amount of 141,087,038.92 cubic meters, Xicheng District owns the least of 9,943,012.58 cubic meters; The largest amount of green biomass per unit area is in Shijingshan District, with 0.74 cubic meters per square meter, and the smallest is in Chaoyang district, with only 0.14 cubic meters per square meter. As for the urban six districts of Beijing, the amount of green biomass per unit area green 0.34 m3/m2; the largest amount of green biomass per capita is in Shijingshan District, with 105.79 cubic meters per capita, while the Western District owns the least green biomass with only 6.06 cubic meters per capita; To ecological benefits, the forestry can product 804981.18t oxygen annual in six districts,the annual absorpted carbon dioxide 1109914.57t, the annual absorpted sulfur diocide 1209.36t,the annual dust reduce quantity 439042.45t, in which the annual absorption tanke up account for 1.02% emission,the annual dust reduce quantity is 7.11 times of dust fall quantity, tthe ecological benefits of green plants in central six districts can play a role in improving the environment in whole. By analysis, suggestions have been proposed from the following three aspects:increase tree number and vertical planting, improve the planning system of green land, set standards of estimating three dimensionnal green biomass as well.Innovation of this paper is shown as follows: (1) In recent years, many scholars have done a lot of research in the three-dimensional green biomass, but for most studies, the volume formula of crown is selected by measuring the factors like tree diameter at breast height, crown width, to estimate the volume. However, this calculation is too extensive, and in this paper three-dimensional laser scanner was used to scan the trees in different directions to the complete point cloud data of the whole trees. And in the post-processing software, three-dimensional point cloud model of the crown has been generated. The model was put into equidistant partition in the direction of the trunk and crown plane, and then, equidistant partition was also done in the direction of the horizontal crown plane, generating several ladder and two drive end to end triangle. In addition, the coordinates of the point cloud bounded by the irregular surface area was calculated. Finally, the crown volume was got based on a number of small round table and two cones, and the whole process was realized by the Program. The results was got by this method, with more accurate results, therefore, the study method is innovative.(2)The paper taking the coordinates of sigle tree obtained by the total station as the origin,one-half the diameter of the crown as radius to establish buffer, and then extracting gray value of the buffers in the image to model.. This method based on pixel gray value and measured tridimentional green biomass is an attempt and exploration, having theoretical meaning in the study of gray value extraction and tridimentional green biomass inversion modeling..(3)The point cloud of single tree got by three-dimensional laser scanner was measured by Geomagic software, to get the measurement factors like crown diameter, tree height, branch height, diameter and others, and then the classical Logistic crown diameter-crown height equation was used for correction. In addition, testing and accuracy evaluation of the model was used to reflect the regression model itself significant, and then measured value and calculated value were used for accuracy assessment. And it was applied to scanning other species to get a Stem-High model with variety of common tree species in urban six districts of Beijing, and this method to study urban vegetation for stem height relations has the practical value and promotion significant. |
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