The Research On Dynamic Monitoring Of Nima District Grassland By Remote Sensing For The Recent 30 Years

Qingzang Plateau is situated at middle and low latitudes, vast,broad and pitched with an average elevation of 4000 meters, known as the "roof of the world" and the "third pole", and with its strong uplift, scenery, rich natural resources unique surrounding region and the extensive and profound influence of global climate and environment, has attracted the attention of scholars at home and abroad. Grassland is the material basis of the development of animal husbandry, especially for the social economical development of Nima district most based on it,but now, Natural grassland in Tibet is faced with the problem of the decreasing in area, the decline in the quality of livestock and conflicts between grass supply and the raising of the livestock, so timely and accurate understanding of the temporal and spatial distribution of grassland resource is very important. Here we can see, the characteristics of remote sensing,which monitor on a large scale and cost a little in time, can grasp the status of grassland resources, provide a strong support for the dynamic monitoring and analysis of grassland management.The research adopting the method of route survey and remote sensing interpretation combined with previous data, the present situation and the ecological environment of grassland shows degradation in grassland in details. A basic research shows that the ecological environment is very fragile, due to the lack of scientific management in grassland resources,overgrazing and excessive herd phenomenon are very prominent, which have resulted in serious degradation of grassland and grassland ecological imbalance, and even the appearance of an immense desertificated area, therefore the protection of the ecological environment and the ecological environment constructions should be in schedule.In the research, Nima district as the object, multi temporal Landsat image datais used,after preprocessing the data, by analyzing the spectral characteristics of grassland resources, using NDVI method to extract the information of grassland resources is calculated, and the classification of the grassland information, temporal and spatial dynamic variation study area in 1988,1999,2009 and in 2015, the monitoring of the grassland.(1) the preprocess of remote sensing dataremote sensing data processing has the following several steps, the first is the radiation correction, which is to eliminate the error produced by the sensor itself with the DN value converted to radiance values, and then the atmospheric correction using the FLAASH model, which is to eliminate the influence of air and light and other factors on the ground reflection. And then re positioning the polynomial correction model, three convolution interpolation re sampling to complete the accurate geometric correction. Finally, the projection transformation by using the ENVI software, which is to ensure that all research data is under the same projection information. The results show that:the model of atmospheric radiation correction and FLAASH correction can eliminate the interference of atmospheric on remote sensing data, ensuring the accuracy of NDVI index.(2) to extract the information of grassland resourcesThe Landsat data pre-processing selects the training sample area to analyze the degree of isolation, supervised classification, and the grass NDVI index obtained by logic operation, according to the trend of NDVI exponential distribution and considering the degree of vegetation coverage, grassland will be divided into 4 levels to ensure the minimum level differences, grade differences, spatial and temporal distribution of rank grass extract in order to get ready for the dynamic research of the future.(3) dynamic monitoring of grassland resourcesThe statistics of the grassland area of different years and of the different-level grassland change. From the perspective of the value of NDVI:the grassland resources in recent 30 years have decreased and different levels of grassland change differently in process of time, the grassland area decreased first and then increased, the low level of grassland and grassland area in grade was first increased and then decreased.(4) analysis and suggestions of the development of grassland change and causesThrough field data information acquisition based on remote sensing data analysis and field investigation, the main reasons of the change of grassland include severe overgrazing, researched area ecological imbalance, rodent rampant weeds, and a series of unsuitable human activities, and here some development suggestions:strengthen the optimization of grassland degradation and desertification of grassland, comprehensive treatment to prevent overgrazing, strengthen the construction of nature reserves, the promotion of solar and other clean energy applications, drinking water projects and water conservancy construction of grassland and grassland sustainable development system construction.In the research,Nima district as the subject,multi temporal Landsat image data and remote sensing are fully used to analyze the spatial and temporal characteristics of grassland in Nima district of Tibet in recent 30 years. The research providing a feasible technology for the analysis of resource information extraction and spatial dynamic of grassland, timely and accurate understanding of the temporal and spatial distribution of grassland resources, has a reference value and guiding significance to promote the development of animal husbandry production and the improvement of the ecological environment.