Lindsey Nicholson

Seventy‐six years of mean mass balance rates derived from recent and re‐evaluated ice volume measurements on tropical Lewis Glacier, Mount Kenya

[1] Lewis Glacier on Mt Kenya has a unique history of detailed study, making it among the best documented tropical glaciers. Here we present (i) a new ice volume determination based on a bedrock DEM constructed from GPR data acquisition and (ii) the glacier’s mean mass balance rates over the last 76 years derived from volume and area estimates based on seven historical maps and the newly determined bedrock topography. Total ice volume in 2010 was 1.90 ± 0.30 × 10 6 m 3 with a mean (maximum) ice depth of 18 ± 3 m (45 ± 3 m), which is one order of magnitude larger than previously published values. In 2010, the glacier had lost 90% (79%) of its 1934 glacier volume (area), with the highest rates of ice volume loss occurring around the turn of the century. Computed mean mass balance rates, covering the whole period of glaciological surveys of Lewis Glacier, provide the longest record of tropical glacier change and show that the mean mass balance rate varies consistently with global estimates, but the magnitude is always more negative than in other regions. Citation: Prinz, R., A. Fischer, L. Nicholson, and G. Kaser (2011), Seventy‐six years of mean mass balance rates derived from recent and re‐evaluated ice volume measurements on tropical Lewis Glacier, Mount Kenya, Geophys. Res. Lett., 38, L20502, doi:10.1029/2011GL049208.

Using Structure from Motion to create Glacier DEMs and Orthoimagery from Historical Terrestrial and Oblique Aerial Imagery

Increased resolution and availability of remote sensing products, and advancements in small-scale aerial drone systems, allows observations of glacial changes at unprecedented levels of detail. Software developments, such as Structure from Motion (SfM), now allow users an easy and efficient method to generate 3D models and orthoimages from aerial or terrestrial datasets. While these advancements show promise for current and future glacier monitoring, many regions still suffer a lack of observations from earlier time periods. We report on the use of SfM to extract spatial information from various historic imagery sources. We focus on three geographic regions, the European Alps, High-Arctic Norway and the Nepal Himalaya. We used terrestrial field photos from 1896, high oblique aerial photos from 1936 and aerial handheld photos from 1978 to generate DEMs and orthophotos of the Rhone glacier, Broggerhalvoya and the lower Khumbu glacier, respectively. Our analysis shows that applying SfM to historic imagery can generate high quality models using only ground control points. Limited camera/orientation information was largely reproduced using self-calibrated model data. Using these data, we calculated mean ground sampling distances across each site which demonstrates the high potential resolution of resulting models. Vertical errors for our models are ±5.4 m, ±5.2 m and ±3.3 m. Differencing shows similar patterns of thinning at lower Rhone (European Alps) and Broggerhalvoya (Norway) glaciers, which have mean thinning rates of 0.31 m a-1 (1896-2010) to 0.86 m a-1 (1936-2010) respectively. On these clean ice glaciers thinning is highest in the terminus region and decreasing upglacier. In contrast to these glaciers, uneven topography, exposed ice-cliffs and debris cover on the Khumbu glacier create a highly variable spatial distribution of thinning. The mean thinning rate for the Khumbu study area was found to be 0.54±0.9 m a-1 (1978-2015).

Can a simple Numerical Model Help to Fine-Tune the Analysis of Ground-Penetrating Radar Data? Hochebenkar Rock Glacier as a Case Study

ABSTRACT Little is known about the thickness of active Alpine rock glaciers, yet they are important components of the local hydrology. We use GPR data to determine the depth of the bedrock of Äußeres Hochebenkar rock glacier (Austria). There is no detailed information available regarding density and composition of the rock glacier, and assumptions about the signal propagation velocity have to be made when processing the GPR data. We use a simple creep model based on surface displacement and slope to calculate the thickness of the rock glacier along a flow line. We calculated bedrock profiles along the flow line for three different time periods, using input from multitemporal digital elevation models. We improved the fit of the profiles by calibrating the values used for layer densities and considered the model valid where the modelled bedrock profiles are within error of each other. We then compared the modeled values with the GPR data to check whether our assumptions for the propagation velocity produced results that match the model. While the fit is good at the lower end of the rock glacier, the GPR data appear to overestimate depth in the upper region. We adjusted the propagation velocity accordingly and find maximum thicknesses of over 50 m and a mean thickness of 30–40 m. The insights gained from the modeling approach thereby improved the fine-tuning of the GPR analysis.

Pléiades Tri-Stereo Data for Glacier Investigations—Examples from the European Alps and the Khumbu Himal

In this study, we use Pléiades tri-stereo data to generate a digital elevation model (DEM) from the Pléiades images using a workflow employing semi-global matching (SGM). We examine the DEM accuracy in complex mountain glaciated terrain by comparing the new DEMs with an independent high-quality DEM based on airborne laser scanning (ALS) data for a study area in the Austrian Alps, and with ground control points for a study area in the Khumbu Himal of Nepal. The DEMs derived using the SGM algorithm compare well to the independent high-quality ALS DEM, and the workflow produces models of sufficient quality to resolve ground control points, which are based on Pléiades imagery that are of sufficient quality to perform high spatio-temporal resolution assessments of remote areas for which no field data is available. The relative accuracy is sufficient to investigate glacier surface elevation changes below one meter, and can therefore be applied over relatively short periods of time, such as those required for annual and seasonal assessments of change. The annual geodetic mass balance for the Alpine case derived from our DEM compares well to the glaciological mass balance, and multitemporal DEM analysis is used to resolve the seasonal changes of five glaciers in the Khumbu Himal, revealing that glaciological processes such as accumulation, ablation, and glacier movement mainly take place during the summer season, with the winter season being largely inactive in the year sampled.

Mass balance processes on glaciers in the Khumbu-Himal (Nepal) based on Pléiades tri-stereo data

In the presented study, we are using Pléiades tri-stereo data to analyse mass balance related processes on several debris-covered glaciers in the Khumbu-Himal region of Nepal. A focus is placed on the important but until now unquantified role of avalanche snow and the influence of rock debris cover on the glacier tongues and the ablation at exposed ice fliffs within the debris. High resolution digital terrain models will be extracted photogrammetrically from the Pléiades scenes, while the optical information will be used for pixel- and object-based surface classification in order to map surface features such as progrlacial lakes, avalance cones and ice-cliffs.

Mapping the snow line altitude for large glacier samples from multitemporal Landsat imagery

The cryosphere of mountain regions is highly sensitive to climate change. This is particularly evident in region wide retreat of glaciers and reduced snow coverage in mountain areas. Snow cover is an important parameter in the glacier mass but also energy balance as it controls the energy fluxes on the glaciers surface and protects the glacier from melt. Monitoring snow cover and the snow line altitude of a glacier through remote sensing data near the end of the ablation season may be considered roughly representative for the equilibrium line altitude on Alpine glaciers which is a useful indicator of the annual mass balance. The aim of this study is to develop an automated tool to retrieve information related to glacier mass balance based on multitemporal satellite imagery and an already existing glacier inventory. The method is developed in the Ötztal Alps where reliable in-situ data are available for several glaciers for a period longer than 30 years. The results show a clear rise of the snow line altitude, which is in agreement with the equilibrium line altitude observed in the field. Nevertheless, the retrieved snow lines by remote sensing imagery are generally too low (> 200 m difference). Part of this underestimate is likely due to the mapping method or the usage of a present DEM which is not representative for historical snow line altitudes. After a proper validation of the current methodology, it can subsequently transferred to other regions in the world.