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Conference Agenda

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Session Overview
Session
C2: ID.10674 Cryosphere Dynamics – Tibetan Plateau
Time:
Tuesday, 05/Jul/2016:
10:30am - 11:30am

Session Chair: Noel Gourmelen
Session Chair: Hui Lin
Workshop: Hydrology & Cryosphere
Location: Building 7-220#, School of Resources and Environmental Science, Wuhan University

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Presentations
Oral presentation

Quick and heterogeneous glacier downwasting at Everest (Qomolangma) from 2000 to 2012 based on bistatic SAR interferometry

Hui Lin1, Gang Li1, Liming Jiang2, Andrew Hooper3

1The Chinese University of Hong Kong, Hong Kong S.A.R. (China); 2Institute of Geodesy and Geophysics, Chinese Academy of Science, China; 3School of Earth and Environment, University of Leeds, UK;

Himalayan and its surroundings distribute the world’s largest low-latitude high-altitude glaciers and contributed about 10% of total glacier mass lost in recent decade. Given the harsh environment of in-situ observations, remote sensing geodetic observation including satellite altimetry, photogrammetry and SAR interferometry are alternatives of mapping glacier height changes. Everest is the hightest mountain in the world, glaciers in this region were mainly controlled by Indian Monsoon. Several long glaciers in this region were heavily covered by debris. In this research, we applied two pairs of X-band bistatic TerraSAR-X/TanDEM-X images obtained in 2011 and 2012 and formed TanDEM-X DEM with bistatic interferometry. Ascending and descending acquisition of SAR images overcome foreshortening, layover and shadow. Cross validation at overlapped glacier region of ascending and descending coverage suggests an RMSE for TanDEM-X DEM of ~2.8 m given the perpendicular baseline at ~150 m. Height difference at off-glacier region suggesting RMSE for differential processing of SRTM and TanDEM-X DEM is better than 4.7 m. By referring to C and X-band SRTM obtained in 2000 we corrected penetration depth and derived decadal glacier height changes. We also extracted glacier flow velocity map by performing feature-tracking method to a stack of L-band ALOS/PalSAR images. Average glacier mass balance for Everest and its surroundings was ~-0.446 m w.e. a-1. No surge glacier was found in this region. Glacier mass lost at south slope (Nepalese side) was a bit more severe than at north slope (Chinese side), which were ~-0.419 m w.e. a-1 and ~-0.481 m w.e. a-1 respectively. The quicker glacier lost rate at south slope could be caused by monsoon weakening in recent decade. Generally debris-cover suppressed glacier mass lost at most elevations bins, however for long and large glaciers such as Rongbuk, at high elevation debris-cover region presented a higher lost rate. This could be possibly caused by lower albedo of debris than clean-ice. At around 5900~5950 m, downwasting rates for clean-ice glaciers and debris-covered glaciers were similar. Fast flow glaciers such as Kangxiong Glacier (also call as Kangshuang) at east slope of Everest, presented low downwasting rate at ~-0.37m w.e. a-1, while Rongbuk Glacier, which flows slowly, presented quicker downwasting rate at ~-0.633m w.e. a-1. The possible explanation for quick flow rate and slow mass lost of Kangxiong Glacier could be its larger accumulation zone. Comparing to glaciers mass balance of previous studies derived by stereo photogrammetry, average glacier lost rate was stable in last few decades for the whole Everest region. However Rongbuk Glacier at north slope presented


Oral presentation

Landsat derived snowline variations in the Nyainqêntanglha Mountains on the Tibetan plateau

Roderik Lindenbergh, Leonoor Portengen, Junchao Shi, Massimo Menenti

Delft University of Technology, Netherlands, The;

Glaciers on the Tibetan Plateau are expected to change, but identifying and quantifying these changes is challenging. One possibility is to check each year where on glaciers bare ice is visible. The accumulation zone, the highest part of the glacier is covered the whole year by snow, while at the ablation zone, the lowest part of the glaciers, the snow that covers the bare ice often completely disappears for some time of the year. The snowline is the line separating snow from bare ice. Snowlines vary throughout the year but are often constant for a fixed period in the year. This more constant snowline gives a rough approximation of the Equilibrium Line Altitude (ELA). When the ELA is decreasing for example, accumulation is greater than ablation and therefore indicates that a glacier gains mass. With upcoming Sentinel 2 data it is expected to be possible to estimate snowlines throughout the Tibetan Plateau at up to weekly intervals, depending on for example local cloud cover.

To obtain experience with snowline estimation, different methodologies were considered and tested on Landsat data sampling several glaciers in the Nyainqêntanglha Mountains in central Tibet. The most promising method to classify snow in Landsat data appears to be the Normalized-Difference Snow Index, which uses the high reflectivity of snow in the visible part of the EM spectrum and the highly absorptivity in the near-infrared/short-wave infrared part of the spectrum. Data used in this study consists of the ASTER GDEM elevation product, of the GLIMS glacier mask and of seven Landsat 7 and 8 scenes from 2000, 2001, 2008 and 2013.

[Figure 1.]

In the figure, snowlines from 3 different years are displayed on a Landsat 8 image from 31 December 2013. Snowline variations between different months in the year 2001 only seem to occur between the wet and the dry season. In June the snowline is much lower than in the winter months, November or February. This wet season is probably caused by the South-East approaching Indian monsoon. Other results seem to indicate that through the years 2001 to 2013 the snowline has risen on the eastern side and has descended on the western side of the study area. Also, there’s more snow present at lower elevations in the northern area than in the southern. For these variations, no clear explanation has been found yet. Possibly explanations can be found in for example albedo differences, or influence of the Westerlies monsoon in combination with orographic precipitation.

Lindenbergh-Landsat derived snowline variations in the Nyainqêntanglha Mountains_Cn_version.pdf
Lindenbergh-Landsat derived snowline variations in the Nyainqêntanglha Mountains_ppt_present.pdf

Poster

Decadal glacier mass balance over West Nyainqentanglha and its contribution to Nam Co Lake Increasing

Gang Li, Hui Lin

The Chinese University of Hong Kong, Hong Kong S.A.R. (China);

The western Nyainqentanglha Range locates in the southeastern center of the Inner Tibetan Plateau (ITP). Glaciers in this region are influenced by both the continental climate of Central Asia and the Indian Monsoon system. Their melting on the western slopes feeds Nam Co Lake, which is the second largest endorheic lake in the ITP. The elevation of Nam Co Lake increased at a rate of 0.25 ± 0.12 m yr-1 from 2003 to 2009 by laser altimeter monitoring. In this study, aimed at quantifying the decadal glacier mass balance in the western Nyainqentanglha Mountains and their increasing melting contribution to Nam Co Lake; we applied the differential Bistatic SAR interferometry method to six pairs of TanDEM CoSSC datasets observed between 2011 and 2014 and SRTM acquired in 2000. The mean annual mass loss rate was -0.185 ± 0.074 m w.e. yr-1 for the entire range. The mass loss rates for the northwestern slope (inside the Nam Co Lake drainage basin) and the southeastern slope (outside the Nam Co Lake drainage basin) were -0.238 ± 0.154 m w.e. yr-1 and -0.169 ± 0.098 m w.e. yr-1, respectively. Our results agree well with previous in-situ observation on glacier mass balance at the Zhadang and Gurenhekou glaciers located on the northwestern and southeastern slopes. Most parts of glacier downwasting occurred at ablation region and accumulation are relatively stable. Debris-cover suppresses glacier downwasting to some extent. However, downwasting rates were higher for the debris-covered and clean-ice sections at high altitude where the debris begins to be exposed. This finding could be caused by the lower albedo of debris than the ice and snow. By presuming that all of the melted ice flows into the lake, the glaciers’ melting contribution to Nam Co Lake’s increasing water volume was approximately 9.35 ± 6.05% during the period between 2003 and 2009.


Poster

Permafrost Distribution in a Characteristic Alpine Watershed in the Source Area of the Yellow River, on the Qinghai-Tibet Plateau

Dongliang Luo, Huijun Jin

Chinese Academy of Sciences, China, People's Republic of;

The controlling factors on permafrost are rather complex on the Qinghai-Tibetan Plateau (QTP), where alpine permafrost mainly occurred in the world. The rugged microtopography and complicated hydrology could account for the spatial heterogeneity of permafrost. In this study, we retrieve the land surface temperature (LST) from the thermal infrared remote sensing data as collected from the Landsat 8 TIRS sensors in a rugged mountainous watershed in the Source Area of the Yellow River (SAYR), Northeastern QTP. And then correlate the LSTs with the digital elevation model (DEM) data derived from the ASTER GDEM products to obtain the lapse rates of LST in this specific watershed. The electrical resistivity tompography (ERT) techniques, detecting the sharp contrast between the frozen and unfrozen states within the sediments, were also employed at an experimental plot in this small watershed. The filed work was carried out in late August and early September in 2015, and the imaging interpretations were validated with ground temperature profiles collected at almost the same time. The explicit boundaries of permafrost base in the experimental plot were detected using specific dielectric properties. Then the spatial distribution of permafrost for the experimental plots were achieved. After the relationship between the LST and specific dielectric properties acquired through validation. The spatial distribution of permafrost is mapped. Preliminary results demonstrate that the thermal infrared remote sensing products and ERT measurements could be useful in detecting the permafrost distribution, even for the complex alpine permafrost regions at mid-latitudes.


Poster

Three-dimensional movements of Siachen glacier derived from D-InSAR and MAI techniques with ERS-1/2 tandem SAR datasets

Daan Li1,2, Liming Jiang1, Yongling Sun1,2, Hansheng Wang1

1State Key Laboratory of Geodesy and Earth's Dynamics, Institute of Geodesy and Geophysics, Chinese Academy of Sciences,Wuhan 430077; 2University of Chinese Academy of Sciences,Beijing 100049;

Glacier surface velocity is one of the key parameters of glacier dynamics and mass balance. Differential synthetic aperture radar interferometry (D-InSAR) has been successfully applied to measuring glacier surface velocity, however, it can only derive one-dimensional surface velocity in line-of-sight (LOS). Multiple Aperture InSAR (MAI) is a new InSAR technology which is sensitive to surface deformation along the radar azimuth direction and can provide complementary information derived from D-InSAR. Therefore, integration of displacement measurements from DInSAR and MAI methods enables us to estimate three-dimensional (3-D) glacier velocities.

In this study, we aim to derive the three-dimensional velocities of Siachen glacier, located in the central Karakoram, by exploiting ERS-1/2 tandem InSAR datasets. Two tandem pairs are used for this purpose, which were acquired on April 1 and 2 1996 (descending track mode) and on May 2 and 3 1996 (ascending track mode), respectively. Firstly, two LOS displacements and two azimuth displacements are derived from D-InSAR and MAI with these ERS1/2 data. Subsequently, the four displacements are applied for deriving 3-D velocities with weighted least squares adjustment. The weights are decided by the precision of each displacement.

The 3-D velocities of Siachen glacier show that the spatial distribution of the glacier movements closely follows the elevation. For the horizontal components, the trunk glacier and the east tributary are active in East-West component, while only the trunk glacier is active in North-South component. This is attributed to the topography of Siachen glacier. The maximum velocities of East-West and North-South components reach up to about 0.54 and 0.92 m/day respectively. For the vertical component, slight uplifting signals are found in the trunk glacier with the maximum value being about +6.0cm/day, while surface lowering emerges in the east tributary with the maximum value being about -4.0cm/day. The accuracies of the 3-D velocities are 4.0, 8.0 and 2.0 cm/day for the East-West, North-South and Up-Down component, respectively. This preliminary results demonstrate the potential of integration of DInSAR and MAI methods for estimating 3-D movements of mountain glaciers.

Li-Three-dimensional movements of Siachen glacier derived_Cn_version.pdf
Li-Three-dimensional movements of Siachen glacier derived_ppt_present.pdf

Poster

Glacial Surface Topography and its Changes in the Western Qilian Mountains Derived from TanDEM-X Bi-Static InSAR

Yafei Sun1,2, Liming Jiang1, Lin Liu1,2, Qishi Sun1,2, Hansheng Wang1

1State Key Laboratory of Geodesy and Earth's Dynamics, Institute of Geodesy and Geophysics, Chinese Academy of Sciences,Wuhan 430077; 2University of Chinese Academy of Sciences,Beijing 100049;

The high-resolution and high-precision glacier surface topography is one of the most important fundamental data for the research of glacial dynamic process of mountain glaciers. The applications of DEM for calculation of glacier slope, extraction of glacier velocity, detection of debris-covered glacier are widely discussed in these literatures [1~3].As more DEM acquisition techniques emerge, it is possible to utilize the multi-temporal glacier DEMs acquired at different times to estimate glacier elevation changes and mass balance in mountain glacier regions [4]. It is noteworthy that the TanDEM-X mission, launched in 2010 by the German Aerospace Center (DLR), opens a new era in single-pass satellite SAR remote sensing. This study aims to quantitatively evaluate the potential of the TDX bistatic SAR data for measuring glacier surface topography and elevation changes over mountain regions.

In this study, we used one pair of TSX/TDX SAR data in bi-static stripmap mode acquired on 21 November 2013. And an bi-static InSAR approach was used for generating TDX DEM. Moreover, glacier elevation changes is employed two methods, The first one is called differential phase method, the other one is DEM differencing method, which will be described in the final paper in detail.

An accurate glacier DEM of the western Qilian Mountain was derived by TanDEM-X bi-static InSAR with TDX SAR data acquired in November 2013. Comparing to independent ICESat elevation footprints, the accuracy of TanDEM-X DEM has reached the HRTI-3 standards with the resolution of 10 m and the elevation accuracy of 1.493±0.75 m, which is also the first high accuracy DEM in western Qilian Mountain region. Additionally, glacier elevation changes results are estimated, which shows that the western Qilian Mountain glaciers are in the negative state as a whole from 2000yr to 2013yr. This study demonstrates the great potential of the TanDEM-X bi-static InSAR technology in mapping surface topography over mountain glacier.

References

[1] D. Scherler, B. Bookhagen and M. R. Strecker, "Spatially variable response of Himalayan glaciers to climate change affected by debris cover." Nature geoscience, 4(3) , pp.156-159, 2011.

[2] Yafei Sun, Liming Jiang and Lin Liu et al. "TanDEM-X Bistatic SAR Interferometry and Its Research Progress" Remote Sensing for Land and Resources, 27(1) , pp.16-22, 2015.

[3] Yafei Sun, Liming Jiang and Lin Liu et al. "Generating and Evaluating Digital Terrain Model with TanDEM-X Bistatic SAR Interferometry" Geomatics and Information Science of Wuhan University, 41(1) , pp.100-105, 2016.

[4] T. Bolch, A. Kulkarni, and A. Kääb, "The state and fate of Himalayan glaciers," Science, 336(6079) , pp.310-314, 2012.

Sun-Glacial Surface Topography and its Changes in the Western Qilian Mountains Derived_Cn_version.pdf


 
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