利用EOS/MODIS数据估算西藏藏北高原地表草地生物量

植被生物量作为一个重要的植被状态参数,其估算不仅对研究陆地生态系统植被生产量、碳循环、营养分配等方面具有重要意义,植被生物量的大小直接影响人类对地表植被的利用特点,而且影响其他的生物物理参量。各种不同空间分辨率、时间分辨率和波谱分辨率遥感数据的出现,使得实时监测大范围的植被生长成为可能。文中根据2004年8月至9月草地植被地面观测资料结合同期的EOS/MODIS卫星遥感数据建立了西藏藏北高原草地植被地上生物量、绿色干物质获得量与EOS/MODIS归一化植被指数(NDVI)、增强植被指数(EVI)之间的关系,并与影响草地植被空间分布的主要气候和高程要素之间的关系进行了分析。结果表明:在藏北高原NDVI较EVI能有效地估算草地地上生物量和绿色干物质获得量;藏北高原草地地上生物量与绿色干物质获得量的空间分布特征是从东南部到西北部逐渐减少,东南部部分地区每平方公顷的草地地上生物量在2000 kg以上,到西北部地区减少到200 kg以下。影响草地地上生物量空间分布的主要气候要素是降水,两者的相关系数为0.64,其次为温度,相关系数为0.44;草地植被地上生物量的空间分布与高程呈反比,即海拔越高的地段生物量越低。

ESTIMATING GRASSLAND BIOMASS IN NORTH TIBETAN PLATEAU USING EOS/MODIS

As one of important biophysical parameters of vegetation,vegetation biomass estimation not only is necessary for studying productivity,carbon circles,and nutrition allocation in terrestrial ecosystem but also important to the natural resources management since the amount of vegetation biomass directly influences human utilization patterns of surface vegetation and affects other biophysical parameters.Remote sensing techniques make it possible that scientists examine properties and processes of ecosystems and their interannual variability,and monitor biophysical parameters such as biomass etc over broad areas at multiple scales because satellite observations can be obtained over large areas of interest with high revisitation frequencies.Vegetation indices such as normalized difference vegetation index(INDV),Enhanced Vegetation Index(IEV) and soil adjusted vegetation index(SAVI) etc obtained from satellite data are useful predictors of biomass and productivity in grasslands.In this paper relationships between the above-ground grassland biomass and green dry matter from the field measurements in North Tibetan Plateau from August to September 2004 and the INDV and IEV from the corresponding MODIS remotely sensed data from the EOS/MODIS Receiving Station in the Tibet Remote Sensing Center and the MOD13Q1 products from LPDAAC with 250 m resolution are established,and the impacts of climate conditions and elevation on the above-ground grassland biomass are analyzed as well.Exponential relations exist between above-ground grassland biomass or green dry matter and vegetation indices(INDV,IEV).The correlation coefficients between above-ground grassland biomass and INDV,and IEV are 0.793,and 0.706;and those between green dry matter and INDV,and IEV are 0.833,and 0.769,respectively.It is apparent that the INDV can more effectively estimate grassland vegetation biomass in North Tibetan Plateau.Furthermore,based on the relationship between INDV and ground data,the spatial distribution of above-ground grassland biomass and green dry matter in North Tibetan Plateau are mapped at a scale of 250 m.The above-ground grassland biomass and green dry matter decrease from above 2000 kg/hm2 in the southeast to blow 200 kg/hm2 in the northwest of North Tibetan Plateau.The main factors affecting the spatial distribution of above-ground grassland biomass in the study area are the precipitation(correlation coefficient= 0.64) and temperature(correlation coefficient= 0.44).There is a negative relationship(correlation coefficient=-0.29) between above-ground grassland biomass and elevation in the study area,which means that the elevation has negative impacts on vegetation productivity in North Tibetan Plateau.