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Canopy closure refers to the degree to which the arbor canopy covers the ground in the forest. It is an indicator reflecting the density of the stand. It is the ratio of the vertical projection area of ​​the canopy of the woodland to the area of ​​the forest land, expressed in tenths, and completely covers the ground with 1, which is 0.9, 0.8, 0.7, ..., 0.3, etc. In practice, the measurement of canopy density is difficult. In general, most of them are measured by the sample method, that is, the sample is laid out at a certain horizontal distance on the diagonal line within the standard ground, and the canopy layer is looked up at each sample point. Dividing the number of samples covered by all canopies by the total number of samples, the canopy closure of the standard land. In recent years, some new methods have been developed, such as Sun Xuewen, etc., using the classification module in arcview to process the canopy photos, estimating the porosity of the canopy, etc. [1], but due to the operator's own measurement level, etc. Factor limits, measurement results are often of varying precision. Based on the previous research, this paper introduces a simple and easy to measure method for determining the canopy density of forest stands. That is to say, the fisheye lens is used to take a full sky photo, and the hemiview canopy analysis system is used to analyze the method and steps of determining the canopy closure degree of the forest at a certain height within the forest.
1 Research areas and research methods
1.1 Research area The research area is located in Mengzi Forest Farm of Mulanweichang State Forest Farm Management Bureau of Weichang County, Chengde City. The larch and larch and spruce plantation are selected as the whole sky photo. The standard area of ​​plantation is designed as 45m × 50m. At the same time, the artificial larch single-layer forest was selected as the control plot, and the plot area was 30m×30m.
The local climate is a temperate continental climate zone. It is long in winter, cold and dry, short in summer, warm and rainy, dry and dry in early spring, and rapid in autumn, often with freezing damage. The vegetation belongs to the temperate steppe zone. The eastern forest steppe area and the temperate coniferous forest area of ​​Yanshan Mountain deciduous broad-leaved forest are connected; the forest is mainly planted, with an area of ​​7900hm2, and only a small amount of natural secondary forest. The plantation forest is a pure coniferous forest dominated by Larix principis-rupprechtii, Pinus tabulaeformis and Pinus sylvestris. The total operating area of ​​the forest farm area is 22667hm2, the forestry land area is 14667hm2, and the total forest accumulation is 745000m3.
1.2 Research method Using a camera with a fisheye lens transducer to take a photo of the stand from a certain height in the stand (full sky photo); calculate the proportion of the space on the full sky photo by the hemiview canopy analysis system, you can get a forest stand Highly transparent porosity.
The fisheye lens is a short-focus ultra-wide-angle photographic lens with a focal length of about 6~16mm. The "fisheye lens" is its common name. The front lens of this photographic lens has a parabolic shape that protrudes toward the front of the lens, which is quite similar to the fish's eyes. Its biggest feature is the wide range of angles of view, the angle of view can generally reach 220 degrees or 230 degrees, can shoot a large range of scenery, providing a good condition for shooting the canopy. Also, since the fisheye lens is an anti-photon optical system with a large amount of barrel distortion, the photograph taken is a central projection on the surface of the sphere. Therefore, we can analyze the canopy closure of the stand by analyzing the photos of this central projection. Therefore, it is a better indicator of canopy closure measurement.
The HemiView canopy analysis system developed in the UK is powerful. Information related to the canopy structure can be obtained by processing image data files, such as leaf area index, light transmission porosity (canopy closure), and gap distribution. By analyzing the full-sky photo taken of the fisheye lens, the canopy closure of the stand can be well estimated.
2. Data Analysis Hemiview Canopy Analysis System Processing Principle The whole sky photo is round, with a zenith angle of 90 degrees at the edge and a zenith angle of 0 degrees. After selecting all the circular parts of the full-sky photo, the hemiview canopy analysis system divides the selected range from the 2.5-degree zenith angle to the full-sky photo 18 every 5 degrees, forming 18 different areas. Ring. Simultaneously,
In accordance with the azimuth in the photo, the area is divided into 8 areas every 45 degrees, so that a full-sky photo is divided into 144 areas, and the aperture area is calculated according to each area. Thereby calculating the porosity of the entire all-sky photo.
3. Computational analysis After a series of processing of the photos, the full-sky photo can be classified and calculated. The pixels in the sky and the canopy in the photo are subjected to extreme processing, and then the area of ​​each partition is calculated. The full sky photo requires a strong contrast between the canopy and the sky, and the analysis system can correctly identify the projection of the sky and the canopy. Through the calculation of a total of 150 photos of 5 plots, the canopy density, light transmittance porosity and leaf area index of artificial stratified forest and single-layer forest were obtained.
4 Conclusions Based on previous studies, this paper introduces in detail the methods and steps for estimating the canopy closure (the complementary value of the transmitted porosity) using the full sky photo and the hemiview canopy analysis system; The speed and accuracy of the degree are greatly improved compared with the previous visual methods. In particular, it provides a scientific basis for various types of project research, ensuring measurement accuracy and improving work efficiency from the data.
Author: Chen Jidong, Ji Xiaolin, Qu Bolin, Zhou Changhong Article ID: 1002-3356 (2007) 04-0005-03
Estimation of canopy closure of artificial stratified forest using hemiview canopy analysis system
Abstract: This paper introduces the application of fisheye lens and photographs of the whole sky, and then uses the hemiview canopy analysis system to analyze the photos to estimate the canopy closure.