Digital Elevation Models for glaciologic applications: An Example from
Nevado Coropuna, Peruvian Andes
(in press, Global and Planetary Change, Special Issue:
Proceedings of the Symposium for mass-balance of Andean glaciers, Valdivia, Chile, March 2003)
Sacred mountains and glacial archeology in the Andes
This reseach focuses on
locating archeologically-senstive areas at high elevations in the Andes. A dataset of existing
high-altitude archeological sites discovered on other mountains
South America has been compiled from previous archeological surveys.
Elevation data from the Shuttle Radar Topography Mission (SRTM) was
used to derive terrain variables (slope, aspect, terrain roughness and shelter index).
Cost surface analysis was used to reconstruct possible Inca climbing routes. Other variables were
derived from paper maps and Digital Chart of the World and were used for the
model input. The
logistic regression analysis produced prbabilities of site presence and
is used to produce maps of potential locations at unsurveyed locations.
The model is validated using archeological sites located on Nevados
Coropuna and Pichu Pichu in Southern Peru, during the field season of
PPT presentation here
Remote Sensing, GIS and Field Techniques for Studying Glacier Changes in the Himalayas: A Multi-Scale Approach Using ASTER Data
There is a paucity of field-based glacier measurements in the high Himalayas due to the difficulty of conducting field campaigns in rugged terrain, lack of logistical support and political/cultural conflicts. This limits our understanding of the temporal and spatial patterns of glacier dynamics and their sensitivity to climate variability across the Himalayas. The proposed research exploits the potential of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensor combined with GIS and field techniques to derive mass-balance measurements and glacial mapping over large areas of the Himalayas using a multi-scale approach. Specific objectives of this research are: 1) to develop and validate remote sensing methods at selected field sites for estimating glacier parameters (area, length, ELA, AAR and mass balance) at the basin scale; 2) to construct a geospatial glacier inventory to facilitate the analysis of glacier changes at the regional scale; 3) to understand spatial patterns of glacier fluctuations in relation to climatic variability at the mountain-range scale; 4) to harvest indigenous knowledge about glacier changes and document water harvesting rituals throughout the Himalaya.
Decadal changes in glacier parameters in Cordillera Blanca, Peru derived from satellite imagery
Comparison of glacier areas from aerial photography and new satellite data has been used extensively in
the last few years to estimate glacier changes in various areas of the world. The tropical glaciers of Cordillera Blanca in Peru (8°30 S, 77°W) have been of interest because of their rapid melting in the last two decades,
posing a threat for local water resources. For the present study, a new set of glacier outlines was produced from 2003 SPOT5 satellite imagery,
with the aim of providing an updated, detailed analysis of ice extent at the present. We compared glaciers from 2003 with the ones from 1970 on a one-to one basis to derive detailed
glacier statistics and changes in glacier elevation and area. The dataset is currently
stored in the
GLIMS Glacier Database , maintained at the National Snow and Ice Data Center (NSIDC),
Boulder. The research was done in collaboration with IRD France (l'Institut de Recherche pour le
Developpement) GREAT ICE project, Glaciology Unit of INRENA (Huaraz, Peru) and the GLIMS project.
This paper evaluates the suitability of readily available elevation data derived from recent sensors - the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the Shuttle Radar Topography Mission (SRTM) - for glaciological applications. The study area is Nevado Coropuna (6,426 m), situated in Cordillera Ampato of Southern Peru. The glaciated area was 82.6 km2 in 1962, based on aerial photography. We estimate the glacier area to be ca. 60.8 km2 in 2000, based on analysis of the ASTER L1B scene.
We used two 1:50,000 topographic maps constructed from 1955 aerial photography to create a digital elevation model with 30 m resolution, which we used as a reference dataset. Of the various interpolation techniques examined, the TOPOGRID algorithm was found to be superior to other techniques, and yielded a DEM with a vertical accuracy of ± 14.7 m. The 1955 DEM was compared to the SRTM DEM (2000) and ASTER DEM (2001) on a cell-by-cell basis. Steps included: validating the DEM's against field GPS survey points on rock areas; visualization techniques such as shaded relief and contour maps; quantifying errors (bias) in each DEM; correlating vertical differences between various DEM’s with topographic characteristics (elevation, slope and aspect) and subtracting DEM elevations on a cell-by-cell basis.
The RMS error of the SRTM DEM with respect to GPS points on non-glaciated area was 23 m. The ASTER DEM had a RMS error of 61 m with respect to GPS points and displayed 200 – 300 m horizontal offsets and elevation ‘spikes’ on the glaciated area when compared to the DEM from topographic data.
Cell-by-cell comparison of SRTM and ASTER-derived elevations with topographic data showed ablation at the toes of the glaciers (- 25 m to –75 m surface lowering) and an apparent thickening at the summits. The mean altitude difference on glaciated area (SRTM minus topographic DEM) was –5 m, pointing towards a lowering of the glacier surface during the period 1955 - 2000. Spurious values on the glacier surface in the ASTER DEM affected the analysis and thus prevented us from quantifying the glacier changes based on the ASTER data.