Improved digital elevation model (DEM) for Lake Eyre, Australia

Here we demonstrate the applicability of using altimetry data and Landsat imagery to provide the most accurate digital elevation model (DEM) of Australia's largest playa lake - Lake Eyre. We demonstrate through the use of geospatial techniques a robust assessment of lake area and volume of recent lake-filling episodes whilst also providing the most accurate estimates of area and volume for larger lake filling episodes that occurred throughout the last glacial cycle. We highlight that at a depth of 25 m Lake Mega-Eyre would merge with the adjacent Lake Mega-Frome to form an immense waterbody with a combined area of almost 35,000 km**2 and a combined volume of ~520 km**3. This would represent a vast water body in what is now the arid interior of the Australian continent. The improved DEM is more reliable from a geomorphological and hydrological perspective and allows a more accurate assessment of water balance under the modern hydrological regime. The results presented using GLAS/ICESat data suggest that earlier historical soundings were correct and the actual lowest topographic point in Australia is -15.6 m below sea level. The results also contrast nicely the different basin characteristics of two adjacent lake systems; Lake Eyre and Lake Frome.

(Table 1) Lake elevation change derived from 4 or more years of measurements

In this study, ICESat altimetry data are used to provide precise lake elevations of the Tibetan Plateau (TP) during the period of 2003-2009. Among the 261 lakes examined ICESat data are available on 111 lakes: 74 lakes with ICESat footprints for 4-7 years and 37 lakes with footprints for 1 -3 years. This is the first time that precise lake elevation data are provided for the 111 lakes. Those ICESat elevation data can be used as baselines for future changes in lake levels as well as for changes during the 2003-2009 period. It is found that in the 74 lakes (56 salt lakes) examined, 62 (i.e. 84%) of all lakes and 50 (i.e. 89%) of the salt lakes show tendency of lake level increase. The mean lake water level increase rate is 0.23 m/year for the 56 salt lakes and 0.27 m/year for the 50 salt lakes of water level increase. The largest lake level increase rate (0.80 m/year) found in this study is the lake Cedo Caka. The 74 lakes are grouped into four subareas based on geographical locations and change tendencies in lake levels. Three of the four subareas show increased lake levels. The mean lake level change rates for subareas I, II, III, IV, and the entire TP are 0.12, 0.26, 0.19, -0.11, and 0.2 m/year, respectively. These recent increases in lake level, particularly for a high percentage of salt lakes, supports accelerated glacier melting due to global warming as the most likely cause.

The Gepatschferner from 1850 - 2006, with links to digital elevation models and glacier margins

This theses investigates changes at Gepatschferner in length, area and volume since the last glacier maximum in 1850. Changes are discussed for the following time periods: 1850-1922, 1922-1971, 1971-1997, 1997-2006. Digital elevation models were created for 1850 from geomorphological data and for 1922 and 1971 from historical maps. Existing DEMs for 1997 and 2006 were further analysed. Since 1850 Gepatschferner has retreated by 2 km in length and has lost 32% of its area and 36% of its volume. The rate of loss of volume is increasing faster than the rate of loss of area and losses in the upper regions of the glacier are becoming increasingly more important to overall losses. The largest losses per 50 m elevation increment occur at the tongue. These losses are greatest in the most recent time step studied, 1997-2006, and exceed previous values by 40% and more. The data base includes the glacier margins, elevations models as they have been compiled within the thesis (DEMs of 1997 and 2006 are part of the glacier inventories, length changes are part of the length change data base of the Austrian Alpine Club).