Cryosphere Monitoring from Satellites and Aircrafts

The cryosphere is collective term for all the components containing frozen water on the Earth’s surface. These components are highly sensitive to changes in the air temperature and precipitation, and hence to climate change. The major components of frozen water in the cryosphere are the ice sheet, ice caps and glaciers.

The Greenland and Antarctic ice sheets alone store a total of 77% of the worlds freshwater in a frozen state, and has the capabilities of increasing the global sea-level with 6 and 65 m respectively. Understanding the changes of the ice sheets in response to climate change is of vital importance to gain insight into the behaviour of these systems and how they affect the global sea level.

Satellite altimetry has for the last two decades been used to monitor the changes of the worlds ice sheets, allowing for the determination of their mass balance. In recent years this has been expanded to both ice caps and glaciers using satellite and airborne altimetry. The research topic of this Ph.D thesis has been to determine and improve the estimation of present-day elevation changes of the ice covered land regions in the Arctic and the North Atlantic by the use of satellite altimetry, such as the ICESat and CryoSat-2 missions, with a specific focus on Cryosat-2.

An central part of the Ph.D study has gone into developing software and algorithms for the utilization of CryoSat-2 data. The investigations has included both development of practical methods for data processing of the ESA level-1 product (L1b) for the estimation of surface elevations and elevation changes over both smooth and complex glacial terrain.

The retrieved surface elevations and elevation changes have been fully validated by comparison with airborne results from ongoing airborne laser campaigns over several types of glacial terrain in the Arctic region. The results from this validation study was then inter-compared with results derived from the ESA L2 baseline-B product to judge the quality of both products.

From this inter-comparison it was shown that the new processing chains, developed in this thesis, performed better than the current ESA L2 baseline-B processing setup. The processing chains developed in this thesis for the CryoSat-2 LRM and SARin-mode showed and average improvement in both accuracy and precision of 50% and 30% respectively, compared to the current ESA L2 baseline-B product.

The development of new surface elevation change algorithms have provided unprecedented coverage of the Greenland Ice Sheet, consisting of more than 17 million surface elevations and elevation change observations. The estimated elevation changes where validated using airborne laser derived elevation changes which showed a correlation of higher than 0.9.

The estimated elevation changes where used to determine the total volume change of the Greenland Ice Sheet, producing an estimate of -224±25 km3a−1 for the period of 2010-2014, which is in good agreement with other studies. This effectively proves that with enhanced processing the CryoSat-2 mission can be used for both large and small scale mass balance studies of ice sheets, ice caps and glaciers.

In the end, the work outlined in this thesis provides many possibilities for improving the current ESA L2 product available to the scientific user.