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

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.