The main objective of the Glaciers CCI project is to contribute to the efforts of creating a globally complete and detailed glacier inventory as requested in action T2.1 by GCOS (2006).
This activity has two major parts:
- Data creation (glacier outlines) in selected and currently still missing key regions
- Establishing a more consistent framework for glacier entity identification to enhance the integrity and error characterisation of the available data sets
As meltwater from glaciers and icecaps provide a substantial contribution to global sea-level rise, the project will also create two additional products in selected key regions, elevation changes and velocity fields.
The work performed in the project follows the tasks as described in the Statement of Work for all CCI projects. The major steps towards the overall project goals include:
- Assessing user requirements regarding product specifications and key regions to be considered
- Developing algorithms for product generation and their evaluation by the community in round-robin experiments
- Preparing illustrated guidelines for generation of the three products (considering a technical and methodological perspective)
- Creating the products and quality assessment
These steps will be performed in close cooperation with the climate research group (CRG) of the project and the participants of the GLIMS initiative.
Methodological uncertainty (glacier area)
One aim of the project is to create vector data sets of glacier outlines in various key regions of the world. These lines are infinitely sharp, but a glacier is actually a fuzzy object that seldom has sharp boundaries. Automated multispectral classification of ice and snow is straightforward and the variety of available algorithms only differ at the level of individual pixels (e.g. Paul and Kääb, 2005). Three other components in the post-classification stage make the ’true’ glacier boundary nevertheless uncertain: debris cover, attached seasonal and/or perennial snow, and the position of drainage divides in the accumulation area. This implies that product accuracy is largely driven by the skills of the analyst and clear guidelines. In the round-robin experiments for the glacier area product, we will focus on these issues rather than on different algorithms for the primary classification of ice and snow.
Sensors and data sets
Product generation will consider a wide range of data sets including satellite images in the optical and microwave range, space-borne altimeters and digital elevation models of varying source, spatial resolution and accuracy. The main data source for the glacier outlines are Landsat TM/ETM+ imagery as available for free from the USGS (glovis.usgs.gov), altimeter data and DEMs for the elevation change product, and data from optical and microwave sensors for the velocity product. A pre-defined set of key regions for product generation is specified in the URD, but this will likely change over time as ongoing glacier mapping activities steadily increase the number of regions covered. Close collaboration with the GLIMS community will hopefully help avoid duplication of work.
Because glaciers are constantly changing, a glacier inventory for an entire region is at best created from data acquired over a short period of time (a few weeks). As a detailed glacier inventory also includes topographic information for each entity (e.g. minimum, maximum and mean elevation), the DEM used to derive this information should be created from data acquired close to the satellite images. Considering that the near-global DEM from SRTM is acquired in the year 2000 and that a high number of Landsat ETM+ scenes are available from the 1999-2003 period, the temporal focus of the project will also be on this period where possible. Since some of the world’s regions’ mapping conditions at the end of the ablation period (or dry season) are constantly poor (e.g. due to clouds and seasonal snow), only the most suitable scenes from the Landsat archive will be selected for product generation and this will include the full time series (1984-2011). For the other products (elevation change and velocity), the time stamp will be driven by data availability.
The Climate Research Group (CRG)
The CRG of the projects includes representatives from the two key science bodies of the project (WGMS and GLIMS), experts from climate (IAC-ETHZ) and hydrological modelling (KfG), as well as scientists responsible for operational glacier monitoring (NVE) and with an overview on the situation in the Himalaya - Hindu Kush region (ICIMOD). The people from these institutions will provide advice on technical issues, help with the implementation of standards and the evaluation of product quality, participate in the round-robin experiments, and give feedback to most of the document deliverables. The CRG is led by Tony Payne from the University of Bristol, who has the required overview on climate-related glaciological research on a global scale.