Mapping and measuring glacier mass balance: developing a best practice approach for understanding glacier change

在全球变暖的气候中，了解全球冰川和冰盖的当前和未来“健康”是一个重要的科学目标。冰川和冰帽一直是，并将在未来几十年成为海平面上升的重要因素。此外，在许多国家，它们对提供水资源至关重要，特别是在旱季，用于人类消费、农业、工业和水力发电。而在其他国家，它们对旅游和娱乐也很重要，至少在地方和区域一级。大量的卫星图像现在可以免费获得，并通过重复调查、DEM差异和季末雪线（ESS）制图，被广泛用于评估全球冰川状况。这种方法特别有吸引力，因为它可以在全球范围内实施，并且应用于图像分类的自动化方法有可能降低工作的劳动强度，甚至提供了生成年度甚至次年度时间序列的潜力。GLIMS（全球陆冰空间测量）和RGI（伦道夫冰川清单）等数据库允许使用大地测量方法（GDM）对冰川和冰盖的质量平衡进行大规模评估，而不需要进行地面物理测量。这对偏远和难以到达的冰川非常有吸引力，例如在北极和高山。此外，卫星图像档案允许生成ESS时间序列，为背景化正在进行的变化提供了巨大的潜力。质量平衡评估的另一种方法是冰川学方法（GLM），这是一种劳动密集型、困难和潜在危险的方法，基本上不包括地球上偏远地区的一些冰川。在冬季和夏季结束时进行重复测量，重要的是可以确定季节和年度平衡。世界冰川监测服务（WGMS）拥有最大的GLM冰川质量平衡时间序列数据集。这些数据可用于确定年度ELAs，并为ESS测量提供误差估计和校正，这代表了本项目的第一个目标：1 -利用GLM质量平衡记录对冰川进行系统的ESS测绘，确定与测量ELAs相比的潜在误差，并确定校正。预计会有显著的区域差异，在质量平衡幅值高的地区，卫星图像产生的短时间序列可能更容易出现误差，而在质量平衡幅值低的地区则不那么容易出现误差。该项目的第二个目标，2 -将是确定从1确定的ESS和测量ela之间误差最稳健的区域。在这些区域内，没有测量到ela的冰川将被绘制成ESS时间序列。根据可用的时间，这些分析将扩展到尽可能多的地区，希望覆盖全球。ESS的时间序列将为在卫星图像记录允许的范围内逐区评估冰川质量平衡变化提供基础。

Background and Rationale Understanding the current and future "health" of glaciers and icecaps globally is an important scientific goal in our warming climate. Glaciers and ice caps have been, and will be for several decades to come, important contributors to sea level rise. Additionally, in many countries they are vital to the provision of water resources, especially in the dry season, which is used for human consumption, agriculture, industry and hydropower. While in other countries they are also significant for tourism and recreation, at least at the local and regional level. Large banks of satellite imagery are now freely available and are now being widely used to assess the state of glaciers globally, via repeat surveys, DEM differencing and end-of-season snowline (ESS) mapping. This approach is especially appealing as it can be implemented globally and automation methods applied to image classification have the potential to reduce labour intensity of the work even offering the potential for generation of annual or even sub-annual timeseries.Databases such as GLIMS (Global Land Ice Measurements from Space) and RGI (Randolph Glacier Inventory) , allow large scale assessments of the mass balance of glaciers and ice caps to be undertaken using the geodetic method (GDM), which does not require on-the-ground physical measurements. This is very appealing for remote and difficult to access glaciers, for example in the arctic and high mountains. Additionally, archives of satellite imagery allow for the generation of time series of ESS offering great potential for contextualising ongoing change. The other approach to mass balance assessment is the glaciological method (GLM), which is labour intensive, difficult and potentially dangerous and essentially excludes some glaciers in the remote regions of the planet. Repeat measurements are undertaken at the end of the winter and summer which importantly allows the determination of seasonal and annual balances. The World Glacier Monitoring Service (WGMS) holds the largest data set of GLM glacier mass balance time series. The data can be used to determine annual ELAs and to provide both error estimation and corrections for ESS measurements and this represents the first aim of this project: 1 - to undertake a systematic mapping of ESS on glaciers with GLM mass balance records, determine the potential error in comparison to measured ELAs and determine corrections. It is anticipated that there will be significant regional differences the short time series generated from satellite imagery may then be more susceptible to error in areas with high mass balance amplitudes, but less so in regions with low mass balance amplitudes. The second aim of the project, 2 - will be to identify regions where the error between ESS and measured ELAs are most robust, determined from 1. Within these regions, glaciers which have no measured ELAs will be mapped to generate a timeseries of ESS. Depending on time available these analyses will be extended to as many regions as possible, hopefully to global coverage. The timeseries of ESS will provide the basis for a region by region assessment of glacier mass balance change extended as far back as the satellite image record will allow.