Application Of DInSAR And Offset Tracking Techniques In Monitoring Mountain Glacier Velocity

Mountain glaciers are sensitive recorders and indicators of global climate change which is also an important source of freshwater resources for human society.Additionally,the movements of glaciers can cause serious natural disasters,such as debris flow and glacial lake outburst floods,that threaten downstream human production and life.Thus,monitoring glacier movement has great significance.This paper will explore the application ability of DInSAR and offset tracking technology based on SAR images in glacier velocity monitoring,and the glacier velocity monitoring experiments are carried out on several selecting study areas.Specific research results and conclusions are as follows:(1)The velocity of Yiga glacier was calculated by applying DInSAR technique to various SAR images.Due to the loss of coherence,only the COSMO-SkyMed image pairs which have 1 day time difference were used to estimate the velocity distribution of Yiga glacier successfully.By comparing the result to the velocity calculated by offset tracking technique,a conclusion can be drew that DInSAR technique can be used to monitoring glacier velocity,but susceptible to the loss of coherence of glacier areas.(2)To improve the offset results which influenced by large spatial baseline and topography when using traditional offset tracking technique applied to extract mountain glaciers velocity,a DEM-assisted offset tracking technique is presented.Two pairs of TerraSAR-X images with different baseline lengths covered Kangma county,Tibet were selected to test the traditional and external DEM-assisted offset tracking techniques in this paper.And the offset results of the two methods in ice-free region were compared.A pair of COSMO-SkyMed images acquired by different beam modes,with different incidence and covering,were select and processed with DEM-assisted offset tracking technique.It is shown that the DEM-assisted offset tracking technique could obtain more reliable offset results than the traditional while the terrain is steep and the spatial baseline is large.The technique can also apply to SAR images which have different beam modes and makes more SAR data useful for glaciers surface movement monitoring.(3)An exploratory research that using the terrestrial 3D laser scanner to measure glacier velocity was carried out in this paper.Two-period point clouds in a small area at the terminus of Pingcuoliesa Glacier was obtained through the use of the 3D laser scanner in the SAR images receiving time period.By comparing the glacial surface velocities estimated by point clouds and offset tracking technique,the reliability of offset tracking technique results was proved.The results indicate that because of the low reflectivity of some glacial surfaces,terrestrial 3D laser scanner may not reliably obtain high-density point clouds,thus limiting its applicability to the study of glacial velocity.Based on SAR data,the offset tracking technique,which can better resist the effects of decorrelation,is more appropriate for monitoring glacial movements.(4)By applying offset tracking technique to ascending and descending COSMO-SkyMed data acquired at nearly the same time and based on four different direction of the Yiga glacier velocities and the geometrical relationships of SAR images,the least square method was used to retrieve the 3D components of the glacier surface velocity in the eastward,northward and upward directions.The results show that applying the offset tracking technique to ascending and descending COSMO-SkyMed images can be used to derive the true 3D velocity of a glacier's surface.And the daily average accuracy of glacier velocity can reach centimeter level.(5)By applying offset tracking technique to long time series Sentinel-1 data,the relationship between the velocities and time was analysed.The results show that the velocities of glaciers vary over time,and changes are mainly relative to the seasonal change in climate change and glacier mass balance.The combination and shift of these multiple factors lead to a common phenomenon that glacial velocities are higher during the spring and summer than in the autumn and winter.