Grain Size Information Acquisition From Erodible Sandy Surfaces Based On Digital Image Processings

China is one of the worst affected countries by desertification all over the world. The area of the desertification accounts for 28% of the whole land. The screening method and wind tunnel test method generally used destroy the original conditions of earth surface. With these methods, it's difficult to do repeatable experiments. Furthermore, when we were in experimental sites, those equipments are limited to electricity and environment. Meanwhile, it's hard to precisely definite the thickness of coarsening slum of earth's surface with wind erosion.These existent monitoring methods draw a conclusion which has a big error and a low precision. It's urgent to improve these methods. In recent years, with the advancement of photo equipment and the development of computer software technology and the remote sensing analysis processing technology, American scientists such as D.J.MacKinnon, Pat S. Chavez, Jr. etc. first research and develop triple-band analysis technology of digital image on sandy surface. For that reason, this study first brings in that technology to China and makes a big improvement. On the base of that technology, we have used ARC-GIS to vectorise the image and detect geometry information about the number of grains. The improved technology processes results accurately and is used extensively. Furthermore, it can exactly and swiftly get hold of the amount of residual coarse sand on earth surface with wind erosion. Therefore, with this technology, we can choose better measures to prevent desertification. It also provides a theory foundation for the sustainable development of husbandry. That is of great importance to the ecological environment and practice of desertification combating in the North West Territories. With the improved technology at its center, this article researches sand, grassland and farmland of the farming-pastoral ecotone of northern China and develops three aspects including screening collecting conditions of digital image, exploring processing technology and assessing the ability of wind erosion resistance in experimental sites. The main conclusions are as follows: (1) The extraction technology about earth surface's coarse graining information with wind erosion on account of digital image processing has been founded. The essential operating standards are as follows:â‘ collect earth surface's digital images;â‘¡use ERDAS-IMAGE to preprocess these images and do statistical analysis on gray scale information;â‘¢apply space model to make different grain types processed;â‘£use ARC-GIS to transform these images and do dislodged analysis;⑤build area compensation equation and calculate. We obtain the practical size of grain, and then divide into different fractions. So we can calculate the amount of residual coarse sand on earth surface and assess coarsening degree with the wind erosion.(2) Precision experiment shows that this technology can extract nearly 100% information of grain quantity and over 90% information of grain geometry. Higher accuracy and smaller error are its distinction. Correlation analysis reveals that coarsening information with wind erosion has evident positive linear relation with size data of soil sample. The relevance coefficient is more than 0.84, and the show level is zero. From the above, we can draw the conclusion that it is feasible to apply this technology to the assessment of wind erosion coarsening degree on earth surface in our country.(3) This article puts forward an indicator to indicate the degree of wind erosion, and this is the design formula: R = ( P₁ -1+P_0.5-0.5)100.(4) The assessment results of wind erosion resistance in experimental sites show as follows: In MuUs sand land, the ability of wind erosion resistance makes difference in different slope aspects. The ability of wind erosion resistance in windward slope is the strongest, while, successively, in left-side ridge line, in right-side ridge line, and in leeward slope. In leeward slope, the ability of wind erosion resistance is the weakest, nearly zero. In the same slope aspect, different slope positions make difference. The ability of wind erosion resistance in the base of slope is the strongest, then; the middle of slope, the top of slope is the weakest. In Xi la mu ren grassland, the abilities of wind erosion in performance area, accommodation and office area, and horse race area are twice higher than that in meadow area. The maximum ability is 0.91. It reflects that modern tourism and economic activity have a serious influence on the grassland area; In the northwestern farming areas of Wuhan county, the ability of wind erosion resistance in abandoned farming land is the strongest, uncultivated land comes second, the weakest is agricultural land. It reflects that farming activity similarly aggravates the wind erosion process. By contrast, modern tourism and economic activity has ten times influence on the wind erosion process as great as farming activity. We can draw the conclusion that modern economic activity has made an unprecedented devastating influence on the environment.