Quantifying Himalayan glacier change from the 1960s to early 2000s, using corona, glims and aster geospatial Data

Doctoral thesis English OPEN
Wilson, R
  • Subject: built_and_human_env

Since reaching their LIAMs, Himalayan glaciers have generally undergone a period of retreat, evident from large moraines left at former ice limits. Currently, however, detailed assessments of Himalayan glacier fluctuations over the past century are limited and fail to compare spatially or temporally to records available in Central Europe, North America and Scandinavia. Consequently, the variability and magnitude of glacial change across the Himalayas, which is a key indicator of climatic change in this region, is yet to be fully understood. \ud \ud Against a background of poor data availability, Corona imagery and historic GLIMS glacier outlines now offer an opportunity to assess glacier extent for regions of the Himalayas pre-1980. Corona imagery, acquired by a US space-borne reconnaissance mission operational from 1960 to 1970, represents a particularly unique dataset offering high resolution imagery (~1.8 m) with stereo-scopic capabilities. Utilising Corona imagery, there is an opportunity to produce detailed maps of Himalayan glacier extent and extract ice surface elevation estimations, in some instances, for the first time. Despite having been de-classified in 1995, the use of Corona data in the Himalayas has been neglected, mainly because of orthorectification challenges related to its unique geometric distortions. Hence, there remains a need to develop a low cost and easily replicable method of accurately orthorectifying Corona imagery enabling its use as a large-scale glacier mapping tool in the Himalayas. In response to this need, Corona images are orthorectified in this study through the use of: (1) a non-metric photogrammetry approach; and (2) horizontal and vertical reference data acquired from ortho-ASTER imagery and the freely available ASTER GDEM. \ud \ud By comparing glacier measurements derived from Corona imagery, GLIMS data and more contemporary ASTER data, changes in glacier area, length and in some instances volume, between the 1960/70s and early 2000s, were quantified for glaciers selected within four study areas located in Uttarakhand, India and Central Nepal. Importantly, this cross-regional glacier change dataset both complements and enhances current Himalayan records. Most notably, results indicate that glaciers selected in the Bhagirathi and Pindar/Kali basins, Uttarakhand, reduced in area by a relatively small 7.97±0.29% and 7.54±0.26%, respectively. Contrastingly, glaciers selected in the more easterly located Seti and Trisula basins reduced in area by 29.78±0.2% and 50.55±0.08%, respectively. Comparisons of Corona DEM (derived from Corona stereo-pairs) and ASTER Global DEM elevations at the terminus regions of four glaciers revealed extensive surface lowering, ranging from 87±27 m to 142±27 m. For Corona processing, the methods applied were shown to orthorectify Corona images to an accuracy that allows comparable glacier outlines to be delineated, further demonstrating the mapping potential of this dataset. However, for Corona DEM extraction, the use of ASTER spatial control data was shown to be inadequate and the presence of large vertical errors in the DEMs generated hindered the measurement of glacier volume change. For this purpose, it is therefore recommended that the methods developed are tested with the use of very high resolution spatial control data.
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    Figure 7.10: Glacier changes from the period of 1959-1975 (outlined in blue) to 2003-2007 (outlined in red) in a portion of the SB site. Background image: Ortho ASTER, 5/10/2003.

    Figure 7.12: Average maximum and minimum ice elevation in 1959-1975 (blue line) in relation to size, and the average minimum elevation of ice in 2003-2007 (red line).

    Figure 7.13: Glacier changes from the period of 1965-1978 (outlined in blue) to 2000-2003 (outlined in red) in a portion of the LT site. Background image: Ortho ASTER, 24/10/2001.

    Figure 7.14: Comparison of absolute area loss and percentage area loss for glaciers within each of the four size classes measured between 1965-1966 to 2000-2003 and 1974-1975 to 2000-2003.

    Figure 7.15: Average maximum and minimum ice elevation in 1965-1975 (in blue) in relation to size, and the average minimum elevation of ice in 2003-2007 (red line).

    Figure 7.16: Distribution of absolute ice area (red and blue columns) and percentage ice area losses (green columns) during 1965 and 2001 at the GC site according to 100 m elevation intervals.

    Figure 7.17: Distribution of absolute ice area (red and blue columns) and percentage ice area losses (green columns) during 1964 and 2004 at the ND site according to 100 m elevation intervals.

    Figure 7.18: Distribution of absolute ice area (red and blue columns) and percentage ice area losses (green columns) during 1959-1975 and 2003-2007 at the SB site according to 100 m elevation intervals.

    Figure 7.19: Distribution of absolute ice area (red and blue columns) and percentage ice area losses (green columns) during 1965-1978 and 2000-2003 at the LT site according to 100 m elevation intervals.

    Bolch, T., Menounos, B., Wheate, R. (2010b.). Landsat-based inventory of glaciers in western Canda, 1985-2005. Remote Sensing of Environment, 114, 127-137.

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