Conference Agenda

Locates at central Himalaya, Mt. Everest (Qomolangma) is the highest peak in the world. Famous glaciers such as Rongbuk glacier and Khumbu glacier were studied by for several long decades. Satellite geodetic observation provides important observation on glacier mass balance in the high-mountain area and plays an essential alternative to in-situ observations given the cold and harsh environment. In this research, we collected SRTM DEM observed in 2000, and bistatic TerraSAR-X/TanDEM-X SAR images observed in around 2013 and 2017. By referring SRTM as reference DEM, we obtained topographic changes between 2000 and 2013, also 2000 and 2017 by using an iterative D-InSAR method. Penetration depth differences between C- and X-band microwave on snow and ice were evaluated and corrected by comparing C- and X-band SRTM DEMs. Glacier mass balance between 2000 and 2013 was -0.38 ± 0.04 m w.e. (water equivalent) a-1, and was -0.75 ± 0.08 m w.e. a-1 between 2013 and 2017. The spatial pattern of the glacier mass loss was heterogeneous. The regional heterogeneity may possibly reflect debris-covering rates, terminating type, temperature rising rates and glacier flow rates. However, the spatial pattern in two periods kept constant. Glaciers without debris-cover at Chinese side present the slowest losing rate while lacustrine-terminating glaciers with heavy debris-covers show quickest lost rates.

Field observations and geodetic measurements suggest that glaciers in the Karakoram Range are either stable or have been expanding since 1990 and present positive or less negative mass changes. This situation is called the “Karakoram anomaly”. Previous studies found that the Central Karakoram has experienced a slight gain in glacier mass at the beginning of the 21st century. Glacier surface velocity is one of the key parameters of glacier dynamics and mass balance. The spatial-temporal characteristics of the glacier velocity in the Central Karakoram are essential to improve our understanding of glacier dynamics and the glacier responses to climate change and influences on regional water sources.

The inter-annual glacier velocity results during 1999-2003 are achieved by using a cross-correlation algorithm in the frequency domain with four pairs of Landsat-7 Enhanced Thematic Mapper Plus panchromatic images. The images were co-registered first, and the horizontal displacements were calculated with the COSI-Corr software package. Due to a lack of in situ measurements of the glacier velocity in the Central Karakoram, it was difficult to directly assess the results of the cross-correlation algorithm. Considering the stable properties of off-glacier areas that should not be displaced, the displacements of the off-glacier area have been widely used to evaluate the cross-correlation performance.

The results show that the variations in ice velocities during 1999–2003 are not obvious for most of the studied glaciers in the Central Karakoram. This indicates that the glacier velocities were quasi-stable during the study period. The uncertainty of the velocity results based on the off-glacier statistics was approximately 7 m/year in the four epochs of observation, which is less than one-half a pixel. We find that most of the glaciers on the southern slope flowed faster than those on the northern slope, which might be attributed to the differences in glacier sizes. From the transverse velocity profiles of seven typical glaciers, we infer that basal sliding is the predominant motion mechanism of the middle and upper glaciers, whereas internal deformation dominates closest to the glacier terminus.

By combusting surface vegetation and soil organic matter, wildfires can have a strong impact on tundra environment. Disturbed vegetation may need many years to recover to pre-fire phase or a mature stage. In this study, we quantified changes of C- and L-band SAR backscatter over 15 years (2002–2016) and used them to investigate vegetation regrowth affected by the Anaktuvuk River Fire in Arctic tundra environment. After the fire, C- and L-band backscatter coefficients increased by up to 5.5 and 4.4 dB in the severely burned areas compared to the unburned areas, respectively. Beyond 5 years after the fire, the C-band backscatter differences diminished between the burned and unburned areas, indicating that vegetation level in burned sites had recovered to the unburned level. This duration is longer than the 3-year recovery suggested by optical-based NDVI observations. Moreover, the L-band backscatter remained about 2 dB higher in the severely burned area than the unburned area after 10-year recovery. Such sustained differences are probably contributed by increased roughness of the surface. Our analysis indicates that long records of space-borne SAR backscatter can quantify post-fire vegetation recovery in arctic tundra environment and complement optical observations.