Spectral Analysis of Different Degradation Level Alpine Meadows in 'Three-River Headwater' Region

The 'Three-River Headwater' region at Qinghai Province is the source region of Yangtze River,Yellow River and Lancangjiang River.At here,grassland is the predominate ecosystem and alpine meadow is the main grassland type.In recent 30 years,large amount of grassland in this area suffered degradation,and therefore monitoring the alpine meadow degradation is important for grassland protection in the 'Three-River Headwater' region.The spectral characteristics of alpine meadow at different degradation levels are valuable information for alpine meadow classification and degradation monitoring through remote sensing.In this study,we measured the ground spectral data and surveyed grass samples in three sorts of alpine meadows at five degradation levels in August 2009 at the 'Three-River Headwaters' Region,Qinghai Province.Then we extracted and analyzed four characteristic values of the collected spectral data: the reflectance at 557675 and 760 nanometer and the red edge slopes.The result indicates that there are little differences among 557 nanometer's reflectance of the three sorts of alpine meadows at five degradation levels,but there are obvious differences among 675 nanometer's reflectance,760 nanometer's reflectance and the red edge slopes.We could distinguish the three sorts of alpine meadows at five degradation levels and make effective monitoring according to those differences.We also calculated the normalized differential vegetation index(NDVI) value of alpine meadow at five degradation levels based on their spectral data and related them with above ground biomass in this study.The result suggests that above ground biomass of alpine meadows at different degradation levels are well related to its 'red edge' slope and NDVI,with the determination coefficient of 0.93 and 0.87 respectively.Thus,these two parameters are useful for above ground biomass estimation based on remote sensing data.The 'red edge' slope of alpine meadows' reflectance not only could distinguish the three sorts of alpine meadows at five degradation levels effectively,but also has a better relationship with above ground biomass than NDVI value.Thus,'red edge' slope of alpine meadows' reflectance is essential for alpine meadows classification,degradation monitoring and biomass estimation.