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He C.,Forest Fire Research Center | He C.,Beijing Forestry University | Gong Y.-X.,The First Institute of Photogrammetry and Romote Sensing | Zhang S.-Y.,Forest Fire Research Center | And 4 more authors.
Guang Pu Xue Yu Guang Pu Fen Xi/Spectroscopy and Spectral Analysis | Year: 2013

Forest fires are harmful to the ecological environment, which have induced global attention. In the present paper fire activities extracted from MODIS and burned areas were compared, and it was found that the wave band of 8~9 extracted from MOD14A1 was useful for fire monitoring, and the data accorded with field investigation with goodness of fit reaching up to 0.83. Through combining this wave band and the relative data to make the time and space analysis of the forest fires for 11 years, from 2000 to 2010, the study showed that the fire occurred most frequently in the spring, the autumn took the second place, and in the summer there was almost no fire occurrence unless drought. Through the analysis of the research area, the burned areas of the coniferous forest and temperate mixed forest were 53.68% and 44%, respectively, while the grassland was only 2.32%. Da Hinggan Ling region was the main combustion area, the burned areas were 64.7% and that for Xiao Hinggan Ling was about 23.49%, while those for other areas were less than 5%. The majority of forest land of burned areas has a gentle slope (≤5°), and is in the middle altitude between 200 and 500 m. So, using satellite remote sensing to analyze the time series of burned areas in forests would make the relationship between the fire activities, climate change, topography and vegetation type clear and it is also helpful to predicting the risk level of the fire areas. Source

He C.,Forest Fire Research Center | Zhang S.,Forest Fire Research Center | Matteo C.,University of Minnesota | Zhou A.,Forest Fire Research Center | Hong F.,Jiangxi Normal University
Nongye Jixie Xuebao/Transactions of the Chinese Society for Agricultural Machinery | Year: 2014

A new algorithm of crown volume based on a square grid method was presented, which was low in cost and high in efficiency and precision, and the normal errors in manual measurement of parameters can be reduced, such as total height, crown width, crown projected area, and so on. While the traditional assessments were not sufficient to provide accurate parameters owing to the irregular crown shapes, and three-dimensional laser was too expensive and fussy to afford. A numerical analysis of the proposed algorithm was presented, along with a design procedure and experimental results. Comparison of obtained results from classical methods and three-dimensional laser measurement was made. The point cloud data were acquired by non-prism total station and a coordinate grid of canopy surface was built, and then the crown volume can be computed with a square grid-based method. Analysis of the parameters had been made with satisfactory precise and the results showed that the relative error of square grid method was 4.13% and the average accuracy was 95.75%. There was no significant difference between calculation value and actual measurement for crown volume under confidence level of 0.05. Moreover, compared to the traditional manual measurement, only one-third of time was consumed by square grid method, which costed 2% of those by three-dimensional laser scanning, therefore, the expenditure was extremely reduced and efficiency was increased. ©, 2014, Chinese Society of Agricultural Machinery. All right reserved. Source

He C.,Forest Fire Research Center | Hong X.,Jiangxi Science and Technology Normal University | Liu K.,Chinese Academy of Forestry | Zhang S.,Forest Fire Research Center | Wang Q.,Forest Fire Research Center
Southern Forests | Year: 2016

An improved technique, cheaper and less time-consuming, to measure standing wood volume by using an electronic theodolite was tested, by which greater information from the forest could be acquired accurately and non-destructively. This was achieved by recording the diameter at breast height and ground-level diameter of a tree as well as the included angle between the electronic theodolite and the left and right tangents of the stem at any point. The standing wood volume then was computed precisely by section. In addition, the factors that influence the precision of the method (observable distance and number of segments) were also analysed. In the study, 175 Larix gmelinii (Rupr.) Kuzen. trees and 190 Populus tomentosa Carrière trees chosen randomly for sampling were measured with the electronic theodolite, and then were cut down for measurement of the average cross-section volume. Based on the data acquired from 100 sample trees, a standard volume table was compiled, and then the data for the remaining random 10 sample trees in each group were selected for a comparison test. The results indicated that the optimal distance for indirect observation should be as high as the sample tree, and the optimal visual distinguished section was about 2 m. The correlation coefficient between the value measured non-destructively and the value of the felled trees of L. gmelinii was 0.97, with an average relative error of 1.62%. With regard to P. tomentosa, the correlation coefficient between the two values obtained by the two methods was 0.905 with an average relative error of 8.40%. It was concluded that the standard volume model based on the non-destructive measurement technique meets the requirements for precision in forest surveys. The precision of the standard volume model for L. gmelinii (a coniferous tree) was superior to that of the model for P. tomentosa (a broad-leaved tree). The electronic theodolite method provides an alternative technique for measuring trees without destructive sampling and is widely applicable for forest surveys. © 2016 NISC (Pty) Ltd. Source

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