联合多种空间测量技术定量分析全球山岳冰川质量平衡

Shrinking mountain glaciers and ice caps, and their seasonally delayed melt water feeding the world's major rivers can significantly affect the stability of freshwater availability especially under anthropogenic climate change. The Asian High Mountain (AHM) glaciated system includes China's Qinghai-Tibet Plateau and borders eight countries. The AHM glaciers and snow covers are sources of 19 of the world's major rivers, bringing water resource to 3 billion people, or 43% of the world's population. It is important to understand the current state of these other glaciers and ice caps in China and in the world. The current knowledge of the contributions of mountain glaciers and ice caps to present-day sea-level rise has a wide range: from 0.55 to 1.4 mm/yr equivalent sea-level rise, and the discrepancy represents a significant amount of freshwater wastage of 304 Gton/yr. We propose to provide an improved quantification of the world's mountain glacier mass balance estimate using a suite of radar altimeter data, not widely used before for glaciers, including CryoSat-2 radar interferometric (SARIn) or SAR altimetry, GRACE gravimetry and ICESat laser altimetry, towards narrowing the uncertainty of mountain glacier's contribution to sea-level rise. Our approaches include: (1) the use of SAR (TerraSAR-X, SRTM-X, ASTER/SRTM-C, ALOS) and CryoSat-2 SARIn radar waveform, along with the new Randolph Glacier Inventory (V2.0) for classifying especially rock glaciers in the AHM glacier regions, to improve the estimates the total glaciated areas needed for computing mass balance, (2) development of land waveform retracking techniques for SARIn/SAR/LRM CryoSat-2, and historic historic and current radar altimeter data (TOPEX, Envisat, Jason-2, AltiKa, HY-2A) to improve glacier elevation retrieval, (3) the use of GRACE gravimetry and ICESat to supplement radar altimetry glacier mass balance time series, (4) the use of ERA-Interim SMB, temperature (MODIS), and if applicable GRACE to estimate firn cmpaction/ice column density corrections, and to mitigate radar penetration errors, (5) to validate resulting mass balance time series using in situ data, other altimeter data and GRACE and to obtain uncertainty estimates. The anticipated results include the generation of a long term, validated and integrated records of radar altimetry, GRACE, and ICESat elevation change, and quantification of the mass balance for the world's mountain glacier systems and ice caps, including China's Qinghai-Tibetan Plateau glacier systems.

为更好的理解"全球海平面变化的物理机制"这一科学问题，本研究提出联合多种空间大地测量技术定量分析和研究全球山岳冰川的质量平衡问题。研究突破传统冰川变化监测技术的局限，结合近年来空间大地测量技术的进展，联合卫星测高、卫星重力以及卫星遥感等多种技术资料精确测定山岳冰川的边界及覆盖面积、监测冰川表面高程的变化，进而精确获得全球山岳冰川质量平衡的变化量，并探讨山岳冰川变化对全球海平面变化的影响。这对我们深入认识全球海平面变化的物理机制以及未来应对措施具有非常重要的作用。

山岳冰川和冰盖的萎缩，及其灌溉着世界主要河流的季节性融水，深刻影响着淡水资源的稳定性，特别是在当前人类因素引起气候变化的大环境下。亚洲高山（AHM）冰川系统包括中国青藏高原并且毗邻八个国家，为19条世界主要河流的发源地，为下游30亿居民提供水资源。了解这些冰川和冰盖在中国和世界上的当前状况十分重要。人们对于山岳冰川和冰盖对当前海平面上升的贡献的估计跨度较大：从0.55到1.4毫米/年，它们的差值相当于304×109吨/年的淡水消耗。本项目使用多种现代大地测量技术的数据，包括ICEsat激光测高；CryoSat-2（低频测高雷达LRM，孔径雷达SAR,及合成孔径雷达SARIn），Envisat，TOPEX及其他测高雷达；GRACE卫星重力数据及地面实测数据来估算和验证2002到2017年间山岳冰川质量变化。我们综合ICESat和CryoSat-2数据得到的2003年10月22日至2017年1月16日期间亚洲高山(AHM)山岳冰川质量变化估值为 –11.02±7.14×109吨/年，其中有1.5年的数据中断。这个估值与几乎同期（2002年4月至2016年7月）的GRACE数据得到的AHM估值 –13.0 ±6.0×109吨/年大致一致。最后我们重新估计得到了世界山岳冰川质量变化为 –152.0 ±9.0×109吨/年（0.42±0.02毫米/年海平面升高），冰盖和末端冰川的质量变化为 –375.0 ±32.0×109吨/年（1.04±0.02毫米/年海平面升高）。与后-气候变化政府间委员会(Post-IPCC)第五次评估报告(AR5)所发布的估值0.76和0.60毫米/年（等效海平面变化）相比，我们估计的山岳冰川融化对当前海平面升高的贡献要显著低0.34毫米/年，冰盖质量平衡估值却高了0.44毫米/年。这导致我们对总冰库（包括山岳冰川和冰盖及末端冰川）变化对当前海平面升高的估值比IPCC AR5给出的估值要高0.10毫米/年。