Recent changes in glacial area and volume on Tuanjiefeng Peak Region of Qilian Mountains, China

Glaciers' runoff in the Qilian Mountains serves as a critical water resource in the northern sections of the Gansu province, the northeastern sections of the Qinghai province, and the northeastern fringe of the Tibetan Plateau. Changes in the glacial area and volume around the highest peak of the Qilian Mountains, i.e., Tuanjiefeng Peak, were estimated using multi-temporal remote-sensing images and digital elevation models, and all possible sources of uncertainty were considered in detail. The total glacier area decreased by 16.1 +/- 6.34 km(2) (9.9 +/- 3.9%) during 1966 to 2010. The average annual glacier shrinkage was -0.15% a(-1) from 1966 to 1995, -0.61% a(-1) from 1995 to 2000, -0.20% a(-1) from 2000 to 2006, and -0.45% a(-1) from 2006 to 2010. A comparison of glacier surface elevations using digital elevation models derived from topographic maps in 1966 and from the Shuttle Radar Topography Mission in 1999 suggests that 65% of the grid cells has decreased, thereby indicating that the glacier thickness has declined. The average change in glacier thickness was -7.3 +/- 1.5 m (-0.21 +/- 0.04 m.a(-1)) from 1966 to 1999. Glaciers with northeastern aspects thinned by 8.3 +/- 1.4 m from 1966 to 1999, i.e., almost twice as much as those with southwestern aspects (4.3 +/- 1.3 m). The ice volume decreased by 11.72 +/- 2.38x10(8) m(3) from 1966 to 1999, which was about 17.4% more than the value calculated from the statistical relationship between glacier area and volume. The relationship between glacier area change and elevation zone indicates that glacier change is not only dominated by climate change but also affected by glacier dynamics, which are related to local topography. The varied response of a single glacier to climate change indicates that the glacier area change scheme used in some models must be improved

The glaciers climate change initiative: Methods for creating glacier area, elevation change and velocity products

Glaciers and their changes through time are increasingly obtained from a wide range of satellite sensors. Due to the often remote location of glaciers in inaccessible and high-mountain terrain, satellite observations frequently provide the only available measurements. Furthermore, satellite data provide observations of glacier character- istics that are difficult to monitor using ground-based measurements, thus complementing the latter. In the Glaciers_cci project of the European Space Agency (ESA), three of these characteristics are investigated in detail: glacier area, elevation change and surface velocity. We use (a) data from optical sensors to derive glacier outlines, (b) digital elevation models from at least two points in time, (c) repeat altimetry for determining elevation changes, and (d) data from repeat optical and microwave sensors for calculating surface velocity. For the latter, the two sensor types provide complementary information in terms of spatio-temporal coverage. While (c) and (d) can be generated mostly automatically, (a) and (b) require the intervention of an analyst. Largely based on the results of various round robin experiments (multi-analyst benchmark studies) for each of the products, we suggest and describe the most suitable algorithms for product creation and provide recommendations concerning their practical implementation and the required post-processing. For some of the products (area, velocity) post-processing can influence product quality more than the main-processing algorithm

Assessment of glacier volume change using ASTER-based surface matching of historical photography

Glaciated regions are known to be particularly sensitive to climate change. Historical archives of glacier volume change are important, as they provide context for present-day changes. Although photogrammetric archives exist for many regions, their usefulness is often limited by a lack of contemporary ground control. High quality digital elevation models (DEMs) underpin a range of change analysis activities. This paper presents a cost-effective solution which utilizes Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) DEMs as control for the scaling and orientation of archival data sets. Instead of relying upon ground-control points, a robust surface matching algorithm is employed to automatically determine the transformation required to register two overlapping DEMs. Through application to the Slakbreen glacier system in Svalbard, Norway, the strategy is assessed by first matching an ASTER DEM to a fixed lidar reference surface. This demonstrates that ASTER DEMs are effectively correct in scale, supporting their use as a control surface. The second stage of the research implements this by matching an aerial photogrammetric DEM to an ASTER reference surface. Resultant volumetric and annual elevation change rates are compared to those derived from lidar data, which are considered in this paper as a truth data set. ASTER-based matching produced a mean annual elevation change rate of -4.12 ma-1, compared to a value of -4.11 ma-1 derived from the lidar data. In volumetric terms, this equates to a difference of 0.6%. A major advantage of this approach is the near-global coverage offered by ASTER data and the opportunity that this presents for remote glacial change analysis over regional extents

Elevation changes of mountain glaciers in the Antarctic Peninsula using ASTER-controlled archival aerial photography

PhD ThesisOver the last 50 years a significant increase in the atmospheric and upper ocean temperatures in the Antarctic Peninsula (AP) region has been observed. As a result major ice-shelves have retreated during the 20th century. In connection, glaciers have accelerated and an increased dynamic ice mass loss is observed, especially over the last decade. Despite these major changes, an exact quantification of ice mass changes of the AP, with its roughly 1000 glaciers, is not available. Almost no long-term (multi-decadal) glacier mass balance records for the AP exist and in-situ measurements are rare. On the other hand, the United States Geological Survey (USGS) and British Antarctic Survey (BAS) archives hold a large number of historic aerial stereo-photographs of the AP, dating back to the early 1940s. These images contain a valuable source of information and have been used to demonstrate widespread retreat of glaciers in this region. Less effort has been made so far to use this stereo-photography for the extraction of elevation data to compare it with recent elevation information to determine glacier volume change from which mass changes may be estimated. This dissertation seeks to close this research gap and to extend the number of mass balance records for the AP, by investigating, measuring, and analysing historical glacier elevation change in the AP using digital elevation models (DEMs) derived from USGS and BAS airborne (1948-2005) and ASTER spaceborne (2001-2010) stereo imagery. To ensure reliable and accurate measurements of surface elevation change, extracted DEMs need to be registered in a precise manner. The lack of ground control information in the AP is a major obstacle for this and can result in inaccurate absolute orientations of DEMs. If uncorrected, possible offsets between DEMs introduce significant error and i can lead to an over- or underestimation of glacier change. Thus, in order to precisely co-register corresponding historic and modern DEMs an iterative robust least squares surface matching algorithm was applied. The underlying surface matching approach was previously developed for small-scale coastal erosion studies at Newcastle University. Within the context of this work it has been successfully modified and improved to enable large scale glacier change assessment in areas of steep topography which is typical for the AP. For a total of 12 glaciers in the AP, located along the western coast between 64° and 71° S, DEMs from the historic archive stereo-imagery were successfully extracted and combined with DEMs derived from modern aerial and ASTER satellite imagery. The improved surface matching approach allowed precise co-registration of these DEMs and enabled the accurate measurement of glacier surface mass balance at the lower portion of the glaciers. Widespread frontal glacier surface lowering, of up to 50 m, has been observed on 12 glaciers with a mean lowering rate of 0.28 ± 0.03 m/yr over a period of 37 years (1970-2007). Higher rates, of up to 0.6 m/yr, were observed in the north-western Peninsula. Two glaciers which have multi-epoch coverage show a significantly larger-than-average lowering since about 1990. These results are in close correspondence with an increase in positive degree days over the last four decades and suggest that much of this lowering can be attributed to atmospheric forcing. However, the observed spatial and temporal variations in the lowering rates suggests that the pattern of surface change is not a simple one and that a regional upscaling is not straight forward. The glaciers represent only 1.2 % of all estimated glaciers in the AP and only the glacier fronts (~20 % of each glacier) were studied. Observations also show an elevation increase at some higher altitude locations within a few km of the glacier fronts, raising the potential that the lowering may have been at least partially compensated for by increased high-altitude accumulation.British Geological Survey BUFI and NER

Geomorphometric analysis and sediment dynamics in mountainous basins: spatial and temporal scales

In this work geomorphometric methods were applied at different spatial and temporal scales for the analysis of the sediment dynamic related to debris flows and bedload sediment transport in alpine environments. The thesis involves two kinds of analysis. The first is aimed at investigating morphological changes occurred in a six years period in two catchments (Gadria and Strimm) of Venosta valley (Eastern Alps, Italy). The study areas were analyzed from both a quantitative (volumetric and areal variations) and qualitative (spatial distribution pattern of erosion and deposition) perspective. The multitemporal analysis was performed by calculating the digital terrain model (DTM) of Difference (DoD) obtained from the comparison of high resolution DTMs (2m), related to both studied catchments, derived from successive LiDAR surveys. A method based on fuzzy logic that takes into account the spatial variability of DTM vertical error was applied to derive the DoD. To evaluate the uncertainty in both pre-event and post-event DTMs, two geomorphometric parameters, i.e., ground point density and slope, approximating the quality of the DTM and the topographic complexity of the study area, respectively, were considered. Volumes of sediment eroded and deposited by events occurred in the analyzed period, as computed by the DoD, were compared to field survey data derived from a database of historical events provided by the Autonomous Province of Bolzano. The use of a spatially variable uncertainty permitted both to recover the information related to low magnitude changes in gentle slope areas that would be lost if a uniform threshold was applied. The analysis also highlighted the possibility to use the DoD for the identification of erosion and deposition processes in uneasily accessible areas and of events that could not be detected through field surveys. The analysis of the relationship between geomorphometric parameters, such as curvature (planform and profile), slope and drainage area, and geomorphologic changes detected by the DoD, improved the qualitative interpretation of surface variations, integrating the volumetric estimates of erosion and deposition. The second analysis involves the investigation of sediment connectivity at different spatial scales both in terms of DTM resolution and geographic extent. The analysis was carried out by using the index of connectivity (IC) proposed by Borselli et al. (2009) and modified by Cavalli et al. (2013) for the analysis of alpine catchments. IC applied to high resolution DTMs allows the spatial characterization of the potential sediment connectivity between hillslope and areas of particular interest (e.g. road, basin outlet, channel). The feasibility of applying IC at regional area (Venosta valley) presenting high topographic and land use variability was tested. In particular, the effect of the DTM resolution on IC results and the variability of the index applied to selected basins of Venosta valley characterized by different shape, size, slope and sediment dynamics, was investigated. The dependence of the sediment connectivity index on the drainage area, mainly due to the downslope component of the index that considers the length of sediment pathways to reach a target or a sink, implies that only basins of similar size can be compared. DTM resolution affects not only mean values of IC but also the spatial distribution of the sediment connectivity both at basin and regional scale. Nevertheless, the obtained results highlight the possibility to apply the connectivity index for a rapid spatial characterization of the sediment connectivity at large scale and in areas characterized by complex morphology and different sediment transport processes such as debris flows and bedload transport. The two analyzed scales, spatial and temporal, even if presented separately in the thesis, can be considered connected. The application of the connectivity index in a basin undergoing glacier retreat (Zinal glacier, Switzerland) allowed the evaluation in a future scenario of the melting process on the potential sediment connectivity after a period of fourty years. Qualitative analysis of the variation of the geomorphologic index suggested that the degree of sediment connectivity is a key factor in controlling the release of sediment between hillslopes and main channel and that future sediment fluxes coming from the melting zone critically depend on the lateral moraines development. As a general conclusion of this study, the high resolution of digital terrain models derived from LiDAR surveys, coupled with the use of suitable tools for geomorphometric analysis, permitted both to evaluate geomorphic changes, caused by multiple events, occurred at basin scale and to create scenario map of the potential sediment connectivity at different spatial scales, in areas characterized by different morphology and sediment transport processes

Elevation change and mass balance of Svalbard glaciers from geodetic data

This thesis uses ground-based, airborne and spaceborne elevation measurements to estimate elevation change and mass balance of glaciers and ice caps on the Svalbard archipelago in the Norwegian Arctic. Remote sensing data are validated against field measurements from annual campaigns at the Austfonna ice cap. A new and more accurate DEM of the ice cap is constucted by combining SAR interferometry with ICESat laser altimetry. The precision of the DEM is sufficient to correct ICESat near repeat-tracks for the cross-track topography such that multitemporal elevation profiles can be compared along each reference track. The calculated elevation changes agree well with more accurate elevation change data from airborne laser scanning and GNSS surface profiling. The average mass balance of Austfonna between 2002 and 2008 is estimated to -1.3 ± 0.5 Gt y-1, corresponding to an area-averaged water equivalent elevation change of -0.16 ± 0.06 m w.e. y-1. The entire net loss is due to a retreat of the tidewater fronts. Earlier time periods are difficult to assess due to limitations in the amount and quality of previous elevation data sets. Other Svalbard regions have been precisely mapped by aerial photogrammetry, so the ICESat profiles from 2003-2008 can be compared with existing topographic maps and DEMs from 1965-1990. The mass balance for this period is estimated to -9.7 ± 0.6 Gt y-1 (or -0.36 ± 0.02 m w.e. y-1), excluding Austfonna. Repeat-track ICESat data are also analysed for the entire Svalbard yielding an average 2003-2008 mass balance of -4.3 ± 1.4 Gt y-1 (or -0.12 ± 0.04 m w.e. y-1) when tidewater front retreat is not accounted for. The most accurate elevation change estimates are obtained using all available ICESat data in a joint regression where surface slope and elevation change are estimated for rectangular planes that are fitted to the data along each track. The good performance of the plane method implies that it can also be used in other Arctic regions where accurate DEMs typically are not available