3-D movement mapping of the alpine glacier in Qinghai-Tibetan Plateau by integrating D-InSAR, MAI and Offset-Tracking: Case study of the Dongkemadi Glacier

Three-dimensional (3-D) movements of the Dongkemadi Glacier in the Qinghai-Tibetan Plateau over 2007-2010 are fully determined by using L-band Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) ascending and C-band Environmental Satellite (ENVISAT) Advanced Synthetic Aperture Radar (ASAR) descending acquisitions. In order to yield an optimal 3-D solution, a variance component estimation (VCE) algorithm is applied to weigh the D-InSAR and MAI measurements derived from PALSAR data and the Offset-Tracking measurements from ASAR data under the scheme of weighted least squares adjustment. By exploiting the InSAR measurements themselves to determine the weights iteratively, the presented approach results in an accuracy of centimeter to decimeter per year for all the three velocity vectors. The horizontal component shows that the four main tributary streams in the Dongkemadi Glacier are all flowing from the central area of the glacier to its surroundings, along the steepest slope descent direction and with a rate up to about 5. m/yr. The glacier thickening or thinning is resolved from the vertical component by subtracting the down-slope movement. A number of interesting accumulation and ablation areas are also detected, with vertical variations of 1-2. m/yr, as a result of the horizontal glacier movement or the existence of concave terrain. This can be used as a good indication of the ice dynamics and the location of the subglacial water in the alpine glacier.