Satellite Estimates and Change Detection of Net Primary Productivity of Oasis-Desert Based on Ecosystem Process with Remotely Sensed Forcing in Arid Western China
干旱生态系统净初级生产力估算及变化探测

Arid and semi-arid ecosystems exhibit a spatially complex biogeophysical structure. According to arid western special climate-vegetation characters, the fractional cover of photosynthetic vegetation (PV), non-photosynthetic vegetation (NPV), bare soil and water are unmixed, using the remote sensing spectral mixture anaysis. We try the method to unmix the canopy funcation sturcture of arid land cover in order to avoid the differentiation of regional vegetation system and the disturbance of environmental background. We developed a modified production efficiency model NPP-PEM appropriate for the arid area at regional scale based on the concept of radiation use efficiency. The model referring to the GLO-PEM and CASA model was driven from remotely sensed observations. The model calculates not just the conversion efficiency of absorbed photosysnthetically active radiation but also the carbon fluxes that determine net primary productivity (NPP). We apply and validate the model in Kaxger and Yerkant river basins in arid western China. The NPP of the study area in 1992 and 1998 was estimated based on the NPP-PEM model. The results show that the improved PEM model, considering the photosysnthetical activation of heterogeneous functional vegetation, is in good agreement with field measurements and the existing literature. An accurate agreement (R2 = 0.85, P < 0.001) between estimates and ground-based measurement was obtained.