Study On Estimation Method Of Natural Grassland's Standing Grass In Cold Season

This paper chooses Xilinguole pasture as the study area. Using MODIS data and ground survey data, this paper exploringly researches the method and technical means that estimate grass standing crop of nature grassland in cold season by remote sensing. We not only propose the method how to count the dry grass index but also study how to establish estimation model of grass standing crop using the dry grass index. We also analyse the changing law of grass preserving rate in cold season using the ground survey data. Basing on this, we analyse the spatial distribution characteristics and changing law of grass standing crop in study area. The results show that:1. This paper proposes dry grass index's counting method. The dry grass index and the ground grass standing crop exists the better correlation, which are extremely significant positive correlation or significant positive correlation. It is feasible that build remote sensing estimation model of grass standing crop in cold season using the dry grass index.2. There is different correlation between dry grass index and grass standing crop of dissimilar pasture. Among the four grasslands, the meadow steppe has the highest correlation, the typical steppe takes the second place and the desert steppe and the sand vegetation have less correlation.3. This paper builds the look-up table of dry grass index based on grass preserving rate of standing crop. The look-up table can exactly obtain the information of the herbage under the snow. It overcomes the obstacles that can't obtain the information of the herbage under the snow by remote sensing, and offer a pratical and effective mothed for coming study.4. Aiming at different grasslands, we build the best estimation model of grass standing crop every month. Through confirmation ananlysis, the estimation model of meadow steppe has higher precision every month, which are about 85%. The precison of the other grasslands'model are more than 60%, except desert steppe in January, which is 56.37%.5. The grass preservation rates of meadow steppe, typical steppe, desert steppe and sand vegetation in the late cold season(April) are 20.36%,14.76%,3.32% and 4.02% respectively, average month decrease rates are 13.27%,14.21%,16.11% and 16.00%.6. The spatial distribution characteristics of grass standing crop in October keep consisitent with growing season. The meadow steppe has the highest yield, the typical steppe takes the second place, and the desert steppe has the least crop. With the passage of time, the spatial distribution characteristics of grass standing crop change correspondingly in cold season. At the early stage of cold season, the grass standing crop mainly distribute on two grades(500-700 kg/ha and 700-1000 kg/ha). At the late stage of cold season, the standing crop dominate by < 100 kg/ha and 100-300 kg/ha. The distribution area of higher yield grade trends to disappear.