## 2 Materials
### COSMO-SkyMED One-Day Tandem DDInSAR  
Campbell Glacier is one of the fastest glaciers in East Antarctica. With a revisit cycle of more than 10 days for conventional single-satellite repeat pass interferometry, the fast-flowing glaciers would have very low coherence, making it difficult to observe surface displacement using DInSAR. COSMO-SkyMED is a constellation of four satellites equipped with X-band SAR (center frequency of 9.6 GHz). Each satellite of the constellation has a repeat cycle of 16 days; however, interferometric observation can be achieved in a day by sharing the same orbital plane [23]. Therefore, the COSMO-SkyMED one-day tandem pair is currently unique for the study of the fast-flowing downstream of Campbell Glacier. A total of 28 COSMO-SkyMED SAR images acquired with 3 m resolution in strip-map mode, VV-polarization, and an incidence angle of 40\({}^{\circ}\) in descending node from June 2010 to November 2011 were used in this study (Table 1).  
The InSAR is a technique for mapping surface topography and displacement from the phase difference of two or more SAR images acquired in the same area. The InSAR processing was performed by using SNAP software provided freely by European Space Agency. Firstly, a one-day tandem interferometric pair of COSMO-SkyMED SAR data were co-registered with one over 32 nd pixel accuracy to generate an initial interferogram. The initial interferogram includes the phases due to the earth ellipsoid, surface topography,  
Figure 1: Map of the study area. The white rectangle is the COSMO-SkyMED SAR image area and the lines are the helicopter-borne IPR survey routes over Campbell Glacier with different colors of acquisition data quality: blue (good), yellow (poor), and red (erroneous).  
surface displacement, and noise. The surface displacement is derived by removing the ellipsoidal earth phase and topographic phase from the initial interferogram. The phase from the noise is very small compared to that from the surface displacement of the glacier, which can be neglected. TanDEM-X 12 m digital elevation model (DEM) provided by the German Aerospace Center was used to eliminate phase from earth ellipsoid and topography from the interferogram and to generate DInSAR image. Goldstein phase filtering was applied to enhance the signal to noise ratio of the interferogram. A total of 14 one-day DInSAR images were generated from June 2010 to November 2011. The resulting DInSAR images include interferometric signals from glacier flow and also tidal deflection in the ice shelf or glacier tongue [19]. If glacier flow is constant over time, it can be cancelled by subtracting two DInSAR data, which is the concept of DDInSAR used to highlight diurnal change of tidal deflection of a floating glacier [19].  
For grounded ice, the DDInSAR can be used to detect the difference of velocity field between the two DInSAR data. For DDInSAR operation, unwrapping the DInSAR phase was performed by using SNAPHU software [24] and the subtraction was also done by using the band math functions of SNAP. The first DInSAR pair [20100616_20100617] was used as a master data for all DDInSAR operations. Except for the Campbell Glacier Tongue, the DDInSAR phase would be constant for the stable regions and constant-flowing glacier surface. As exceptions to this, velocity anomalies over grounded glacier will be reported in Section 3.