Bavarian Academy of science and Humanities

Garching bei München, Germany

Bavarian Academy of science and Humanities

Garching bei München, Germany
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Kriegel D.,German Research Center for Geosciences | Mayer C.,Bavarian Academy of science and Humanities | Hagg W.,Ludwig Maximilians University of Munich | Vorogushyn S.,German Research Center for Geosciences | And 3 more authors.
Global and Planetary Change | Year: 2013

Glaciers are significant fresh water storages in Central Asian high mountains and are considered to substantially contribute to the summer runoff of Central Asian Rivers. We present a comprehensive study of the glacier area changes in the Naryn catchment located in the Tien Shan Mountains. The catchment with a size of 55,944km2 is a major tributary of the Syrdarya River which is heavily used for water supply and irrigation. We analysed the glacier retreat based on Landsat MSS, TM and ETM+imagery for the mid-1970s, late 1990s and mid-2000s and based on a SPOT scene for 2007. Our results show a decreasing glacierisation within the catchment, shrinking from 1210±30km2 (2.2% glacierisation) in the 1970s to 1019±25km2 (1.8% glacierisation) in the late 1990s and further down to 926±23km2 (1.7% glacierisation) in the mid-2000s, corresponding to an area loss of 23% in total. The analysis reveals spatially heterogeneous area loss within the catchment. This can be associated with different hypsometries, size distributions, aspects and presences of debris cover. Small glaciers (with an area<1km2) suffered from a strong area loss within the 30-years investigation period. Trends in air temperature, precipitation and positive degree days (PDD) at climate stations suggest that the glacier retreat is likely to be driven by the increasing summer (April-September) temperature, rather than changes in precipitation: In the period from 1960 to 2007, both summer air temperature and PDDs increased significantly at a rate of 0.19. °C/decade and 3.9. °C/decade respectively, whilst for precipitation no consistent trends were detected. However, rigorous attribution of changes is complicated by the variable glacier response times. In the two headwater sub-catchments of the Naryn basin, Small and Big Naryn, positive trends in spring and autumn discharge were detected and are likely to be associated with the enhanced snow and glacier melt driven by increasing temperatures in those seasons. However, no discharge trends in August - the month with the largest expected glacier contribution - were detected. The strong, significantly positive trends in winter and early spring runoff are associated with strongly increasing winter temperatures and number of days with maximum daily temperature above the freezing point causing snow melt. Hence, increasing glacier area reduction can be explained by the prolongation of the melting season reducing accumulation rather than by increasing annual mean temperatures. Despite the high relative changes, the absolute increase in winter discharge is very small. © 2013 Elsevier B.V.

Helfricht K.,Alpdndash Center for Climate Change Adaptation | Helfricht K.,University of Innsbruck | Kuhn M.,University of Innsbruck | Keuschnig M.,Alpdndash Center for Climate Change Adaptation | And 3 more authors.
Cryosphere | Year: 2014

The storage of water within the seasonal snow cover is a substantial source of runoff in high mountain catchments. Information about the spatial distribution of snow accumulation is necessary for calibration and validation of hydro-meteorological models. Generally, only a small number of precipitation measurements deliver precipitation input for modelling in mountain areas. The spatial interpolation and extrapolation of measurements of precipitation is still difficult. Multi-temporal application of lidar techniques from aircraft, so-called airborne laser scanning (ALS), provides surface elevations changes even in inaccessible terrain. These ALS surface elevation changes can be used to derive changes in snow depths of the mountain snow cover for seasonal or subseasonal time periods. However, since glacier surfaces are not static over time, ablation, densification of snow, densification of firn and ice flow contribute to surface elevation changes. ALS-derived surface elevation changes were compared to snow depths derived from 35.4 km of ground penetrating radar (GPR) profiles on four glaciers. With this combination of two different data acquisitions, it is possible to evaluate the effect of the summation of these processes on ALS-derived snow depth maps in the high alpine region of the Ötztal Alps (Austria). A Landsat 5 Thematic Mapper image was used to distinguish between snow covered area and bare ice areas of the glaciers at the end of the ablation season. In typical accumulation areas, ALS surface elevation changes differ from snow depths calculated from GPR measurements by -0.4 m on average with a mean standard deviation of 0.34 m. Differences between ALS surface elevation changes and GPR derived snow depths are small along the profiles conducted in areas of bare ice. In these areas, the mean absolute difference of ALS surface elevation changes and GPR snow depths is 0.004 m with a standard deviation of 0.27 m. This study presents a systematic approach to analyze deviations from ALS generated snow depth maps to ground truth measurements on four different glaciers. We could show that ALS can be an important and reliable data source for the spatial distribution of snow depths for most parts of the here investigated glaciers. However, within accumulation areas, just utilizing ALS data may lead to systematic underestimation of total snow depth distribution. © 2014 Author(s).

Hagg W.,Ludwig Maximilians University of Munich | Mayer C.,Bavarian Academy of science and Humanities | Lambrecht A.,University of Innsbruck | Kriegel D.,Helmholtz Center Potsdam | Azizov E.,Central Asian Institute for Applied Geosciences
Global and Planetary Change | Year: 2013

A glacier inventory referring to the year 2007 was created for the Big Naryn basin based on satellite imagery. The 507 glaciers had a total area of 471. km2. Compared to the Soviet glacier inventory based on data from the mid 20th century, the total glacier area decreased by 23.4%. The shrinkage varies from 14% to 42% between individual mountain ranges. We discuss the possible causes for this considerable variation by analyzing and interpreting topographic parameters and differences between seven sub-regions. On three glaciers, ice thickness was derived by ground penetrating radar (GPR) measurements on the glacier tongues and by surface slope using a simplified ice mechanical approach on the upper parts. We estimate the total ice volume of the basin for both inventories using volume-area scaling. Our results show a current glacier volume of 26.0-33.3. km3. A total of 6.6-8.4. km3 (20%) have been lost since the mid 20th century. The water equivalent of 5.9-7.6. km3 was transformed into excess discharge and contributed to at least 7.3-9.2% of total runoff in the considered period. © 2012 Elsevier B.V.

Araszkiewicz A.,Military University of Technology | Volksen C.,Bavarian Academy of science and Humanities
GPS Solutions | Year: 2016

Precise positioning using the signals of the Global Position System requires correcting the distance between the points of reception of the signal carrier phase and the antenna reference point. Sophisticated models to account for these phase errors are available and widely in use. These models are usually based on calibrations of several antennas of the same type to derive a mean model. There is also the possibility of applying individual correction models that are derived for one single antenna, since the individual antennas may still vary by a few millimeters. We prepared two sets of station position time series to understand the impact of using type mean or individual antenna correction models. At first, we estimated the station positions using the type mean model for the antenna corrections as it is provided by the IGS. Second, the same processing strategy was used, but this time with individual antenna correction models provided they were available. Then, based on these two solutions, we evaluated how different antenna corrections impact the network alignment and subsequently station coordinates. We showed that mixing two sources of antenna phase center corrections may influence the reference frame realization. However, this impact is very small and can be reduced by an appropriate selection of reference stations. Finally, we demonstrated that for some antennas, the application of type mean or individual antenna calibration models may cause a discrepancy in the position of over 10 mm for the horizontal and vertical component. However, for most of the antennas these offsets are below 2 mm for horizontal components and below 4 mm for vertical component. Thereby, for common antennas we confirmed the results obtained by others. © 2016 The Author(s)

Gerlach C.,Bavarian Academy of science and Humanities | Rummel R.,TU Munich
Journal of Geodesy | Year: 2013

One of the main objectives of ESA's Gravity Field and Steady-State Ocean Circulation mission GOCE (Gravity field and steady-state ocean circulation mission, 1999) is to allow global unification of height systems by directly providing potential differences between benchmarks in different height datum zones. In other words, GOCE provides a globally consistent and unbiased geoid. If this information is combined with ellipsoidal (derived from geodetic space techniques) and physical heights (derived from leveling/gravimetry) at the same benchmarks, datum offsets between the datum zones can be determined and all zones unified. The expected accuracy of GOCE is around 2-3 cm up to spherical harmonic degree nmax ≈ 200. The omission error above this degree amounts to about 30 cm which cannot be neglected. Therefore, terrestrial residual gravity anomalies are necessary to evaluate the medium and short wavelengths of the geoid, i. e. one has to solve the Geodetic Boundary Value Problem (GBVP). The theory of height unification by the GBVP approach is well developed, see e. g. Colombo (A World Vertical Network. Report 296, Department of Geodetic Science and Surveying, 1980) or Rummel and Teunissen (Bull Geod 62:477-498, 1988). Thereby, it must be considered that terrestrial gravity anomalies referring to different datum zones are biased due to the respective datum offsets. Consequently, the height reference surface of a specific datum zone deviates from the unbiased geoid not only due to its own datum offset (direct bias term) but is also indirectly affected by the integration of biased gravity anomalies. The latter effect is called the indirect bias term and it considerably complicates the adjustment model for global height unification. If no satellite based gravity model is employed, this error amounts to about the same size as the datum offsets, i. e. 1-2 m globally. We show that this value decreases if a satellite-only gravity model is used. Specifically for GOCE with nmax ≈ 200, the error can be expected not to exceed the level of 1 cm, allowing the effect to be neglected in practical height unification. The results are supported by recent findings by Gatti et al. (J Geod, 2012). © 2012 Springer-Verlag.

Prasch M.,LMU | Mauser W.,LMU | Weber M.,Bavarian Academy of science and Humanities
Cryosphere | Year: 2013

Water supply of most lowland cultures heavily depends on rain and melt water from the upstream mountains. Especially melt-water release of alpine mountain ranges is usually attributed a pivotal role for the water supply of large downstream regions. Water scarcity is assumed as consequence of glacier shrinkage and possible disappearance due to global climate change (GCC), in particular for large parts of Central and Southeast Asia. In this paper, the application and validation of a coupled modeling approach with regional climate model (RCM) outputs and a process-oriented glacier and hydrological model is presented for the central Himalayan Lhasa River basin despite scarce data availability. Current and possible future contributions of ice melt to runoff along the river network are spatially explicitly shown. Its role among the other water balance components is presented. Although glaciers have retreated and will continue to retreat according to the chosen climate scenarios, water availability is and will be primarily determined by monsoon precipitation and snowmelt. Ice melt from glaciers is and will be a minor runoff component in summer monsoon-dominated Himalayan river basins. © Author(s) 2013.

Collier E.,University of Alberta | Collier E.,TU Berlin | Molg T.,TU Berlin | Maussion F.,TU Berlin | And 3 more authors.
Cryosphere | Year: 2013

The traditional approach to simulations of alpine glacier mass balance (MB) has been one-way, or offline, thus precluding feedbacks from changing glacier surface conditions on the atmospheric forcing. In addition, alpine glaciers have been only simply, if at all, represented in atmospheric models to date. Here, we extend a recently presented, novel technique for simulating glacier-atmosphere interactions without the need for statistical downscaling, through the use of a coupled high-resolution mesoscale atmospheric and physically-based climatic mass balance (CMB) modelling system that includes glacier CMB feedbacks to the atmosphere. We compare the model results over the Karakoram region of the northwestern Himalaya with remote sensing data for the ablation season of 2004 as well as with in situ glaciological and meteorological measurements from the Baltoro glacier. We find that interactive coupling has a localized but appreciable impact on the near-surface meteorological forcing data and that incorporation of CMB processes improves the simulation of variables such as land surface temperature and snow albedo. Furthermore, including feedbacks from the glacier model has a non-negligible effect on simulated CMB, reducing modelled ablation, on average, by 0.1m w.e. (-6.0 %) to a total of -1.5m w.e. between 25 June-31 August 2004. The interactively coupled model shows promise as a new, multi-scale tool for explicitly resolving atmospheric-CMB processes of mountain glaciers at the basin scale. © Author(s) 2013.

Maksymiuk O.,TU Munich | Mayer C.,Bavarian Academy of science and Humanities | Stilla U.,TU Munich
Remote Sensing of Environment | Year: 2016

Glaciers are an important climate indicator due to their sensitive dependence upon local and regional climate variables, which makes them worthwhile research subjects. A comprehensive description of the glaciers' interaction with the environment and their dynamical behavior requires complex physical models and the measurement of relevant parameters. In-situ data acquisitions are costly and often spatially sparse due to the large extent of glaciers; however, satellite-based sensors offer timely data with complete ground coverage, making them a good choice for continuous monitoring of glaciers. Synthetic aperture radar (SAR) allows a nearly weather-independent monitoring of glacier motion, which is beneficial for often cloudy regions like Alaska or Patagonia. This paper presents a new workflow for the automatic extraction of glacier surfaces from SAR intensity images and the determination of their velocities involving a fluid mechanics model. An initial motion estimation is obtained from intensity tracking on SAR image pairs and subsequently corrected by a physics-based spatial regularization. The surface velocity is approximated by the two-dimensional Navier-Stokes equation for incompressible fluids. The regularization is formulated as a data assimilation problem in which the final solution is a proper solution of the Navier-Stokes equation and simultaneously fitted to the observed velocity. This partial differential equation (PDE) constrained optimization is solved with adjoint models using finite element methods. The proposed method is evaluated on the Taku Glacier, AK, an outlet glacier of the Juneau Icefield. Our presented approach is independent from the type of sensor as long as initial velocity estimates can be obtained. The final results can be used as input to methods estimating ice volume and thickness. © 2015 Elsevier Inc.

Wang X.,TU Munich | Gerlach C.,Bavarian Academy of science and Humanities | Rummel R.,TU Munich
Geophysical Journal International | Year: 2012

The magnetic field mission Swarm, expected to be launched in 2012, comprises a constellation of three satellites. As all of them are equipped with GPS receivers and accelerometers, they can be used for gravity field recovery. We study the capability of a Swarm-like constellation for (time-variable) gravity field recovery and compare it with a gravity field tandem mission of GRACE-type. Due to the lower accuracy of the GPS measurements compared with GRACE low-low satellite-to-satellite tracking (SST), the accuracy of a Swarm derived gravity field cannot compete with the state-of-the-art GRACE models. However, unlike the GRACE mission, Swarm allows for the derivation of GPS-baselines between the satellites in directions other than purely along-track. This makes Swarm an interesting case for studying the error structure of gravity field models derived from various constellation geometries. Therefore, one focus of this study is the general analysis of different baseline constellations independent of the observation accuracy, that is, we do not restrict ourselves to just the actual Swarm case of pure GPS-baselines. To make the results comparable to GRACE, we explicitly study the error behaviour of the different Swarm baseline geometries assuming GRACE-type K-band ranging (KBR) links. This gives an indication of candidate constellations for future missions; at least in regards to the general error structure. To study the potential of Swarm for recovering time-variable components of the gravity field, we have set up a 2-yr simulation to recover annual and semi-annual components of continental hydrology. We show that Swarm has the potential to recover the annual signal up to spherical harmonic degree 6. This is of interest should there be a gap between the end of the GRACE mission and the launch of a follow-on mission. All our simulations make use of the energy integral method. This method is usually (implicitly) formulated for static potential fields. Therefore, it is necessary for our study to investigate the properties of this method when applied to the analysis of time-variable fields. © 2012 The Authors Geophysical Journal International © 2012 RAS.

Mayr E.,Ludwig Maximilians University of Munich | Hagg W.,Ludwig Maximilians University of Munich | Mayer C.,Bavarian Academy of science and Humanities | Braun L.,Bavarian Academy of science and Humanities
Journal of Hydrology | Year: 2013

We modified the well-known HBV-ETH model to develop a partially distributed hydrological model that was able to simulate runoff in a highly glacierised basin. By introducing additional calibration criteria (annual and winter glacier mass balance) we reduced the goodness-of-fit for runoff, but improved the description of the accumulation and ablation processes involved. Final adjustment of the model parameters, after choosing the best out of 10,000 random parameter sets, allowed us to find a parameter calibration with acceptable errors for all criteria, which was then confirmed by good model performance during the validation period. The glacier-wide winter mass balance and the annual mass balance in the ablation area were simulated well, while the annual mass balance in the accumulation area showed inaccuracies. Good simulation of the processes during the 2003 heat wave in Europe proved that the model also delivers reliable results for meteorological conditions different from those used during calibration. © 2012 Elsevier B.V.

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