草地地上生物量累积速率遥感定量化方法研究：以暖干化的呼伦湖流域为例

Grassland biomass and phenology, as two very important vegetated indictors in the research fields of global change ecology, are sensitive to changes in regional hydrothermal conditions. It is meaningful to take biomass accumulative rate as a link to couple these two factors for understanding integrated impact of regional water cycle and energy exchange on grassland production with global warming. This study will take Hulun lake watershed as a case study area, where climate has a trend of warming and drying over the past few decades. The time series of vegetation index (VI) with a unified spatial-temporal feature will be produced via fusing multi-resource remote sensing data, and then the date of greenup and maturity, as well as the time span of continuing growth will be extracted from the time series of VI. In addition, a pure VI (PVI) derived from decomposing the normal VI (e.g. NDVI, RVI and EVI) will be introduced into the light use efficiency (LUE) approach. With the sample plots of in situ measurements, remote sensing derived estimate model for grassland accumulative above-ground biomass (AGB), which considers the vegetated phenological process from greenup to maturity, will be build. Afterward, grassland AGB accumulative rate will be quantified via compiling grassland AGB model with the time span of vegetated continuing growth. Finally, the study will analyze the inter-annual changes in grassland AGB accumulative rate in Hulun lake watershed, and evaluate impact of climate change, and that mixed with human activities on grassland productivity.

草地生物量与物候期对水热条件响应敏感，是当前全球变化生态学研究中的两个重要植被因子。以草地生物量累积速率为纽带耦合这两个植被因子有助于综合理解变化环境条件下区域水分循环和能量交换对草地生产力的影响，对掌握草地生长动态，指导牧业生产具有重要意义。本研究以气候暖干化的呼伦湖流域为典型研究区，基于多源遥感数据，构建时空一致性植被指数，精确提取草地返青期、生长旺盛期以及持续生长时间；在将净植被指数引入光能利用效率模型的基础上，结合连续观测的野外样地数据，构建考虑物候期变化的草地地上生物量遥感估算模型；在此基础上，利用草地地上生物量与持续生长时间定量估算草地地上生物量累积速率，分析评估呼伦湖流域草地地上生物量累积速率变化规律，阐明气候变化与综合人类活动对草地生产力的直接影响。

草地地上生物量是草地生态系统获取能量的集中表现，对生态系统结构和功能的形成具有十分重要的作用，更为直接的是草地地上生物量是牧业发展重要的物质基础。利用遥感观测方法实现草地地上生物量区域估算已被广泛的使用。但是，由于草地群落结构与组成的差异，草地地上生物量遥感估算模型在实际应用中存在较大的不确定性。项目以“草地地上生物量累积速率遥感定量化方法研究：以暖干化的呼伦湖流域为例”为研究目标，开展了基于PVI模型的星-机-地多尺度卫星遥感应用实验。通过大量的地面实验及其广泛的区域应用，阐明了草地地上生物量遥感估算不确定性的问题及其对气候变化的响应机制，为星-机-地多尺度草地生物量遥感检测提供了理论方法。