| On the basis of runoff, precipitation and remote sensing data of Erjina in recent years, the influence of runoff and precipitation to vegetation coverage of oasis are analyzed by using system method and the model of vegetation coverage to runoff and vegetation coverage to precipitation are developed respectively.The following aspects are discussed:1. Programs including radiometric calibration, projection transform, image clipping, atmospheric correction, geometric rectification and NDVI calculation are designed during the processing of NOAA/AVHRR data (1.1 km resolution) by using remote sensing software. Accumulated NDVI represents the parameter of vegetation coverage of oasis is obtained by adding NDVI which are more than zero.2. According to system theory, runoff and precipitation are considered as motivation to vegetation environmental system while vegetation coverage of oasis is response due to motivation. Therefore, subsystem models of vegetation coverage to runoff and vegetation coverage to precipitation are established by using system method.3.Based on the characteristics that variable frequency of runoff is low and variable frequency of precipitation is high, the low-pass filter is designed to separate the two sorts of different information.4.Principle of hysteresis of vegetation growth to runoff and precipitation is analyzed. Convolution formula is applied to simulate hysteresis of runoff and precipitation and linear equations is listed to solve weight function which can represents hysteresis.5. Weight functions are calculated and compared by selecting different lag-times. It is the most reasonable that the maximum lag-times of hysteresis of runoff and precipitation are 13 days and 3 years.
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