Satellite Monitoring of the Ecological Environment Recovery Effect in the Heihe River Downstream Region for the Last 11 Years

The NDVI of the downstream of Heihe was calculated based on the data derived from Landsat TM/ETM+ images in 2000, 2001, 2002, 2006, 2009, and 2010. The six images all are same season's data, the span of time fall short of one month, so we can ignore error due to seasonal aspect. After the NDVI was calculated, the land cover was divided into five types based on the light of NDVI's value: the water area, the bare land, the sparse vegetation area, the moderate vegetation area and the thick vegetation area. Counting the areas of each grade vegetation zone, and meanwhile combining the information of hydrological observation with through the comparison of the different grade vegetation area and lake area change before and after water division, the restoring effect of the vegetation in the downstream of Heihe can be found out, and this can supply the scientific foundation for the Heihe water-division plan of the next step. The monitoring results show that lake area shrink rapidly and the ecological environment of the downstream of Heihe kept deteriorating before 2002, but after eleven year water division from upper and middle reaches of Heihe river, lake area extension compare quickly, the increment of the sluice is also very obvious, the environment deteriorating was alleviated and vegetation was restoring stage by stage.