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The dynamics of landfast sea ice, also called fast ice for short, has a large influence on the variability of polynyas and marine ecosystems, and the logistics for research stations near the Antarctic coast. Therefore, it is important to accurately measure the strain of fast ice and its seasonal variations, and to identify the cause of stresses on the ice. In this paper, we separate the strains from glacial stress and tidal stress of fast ice near the Campbell Glacier Tongue (CGT) in Terra Nova Bay, East Antarctica. This was done using observations from a series of one-day tandem COSMO-SkyMed Interferometric Synthetic Aperture Radar (InSAR) images obtained from December 2010 to January 2012. Firstly, we discriminated fast ice from pack ice and open water by analyzing the interferometric coherence values. We then identified the characteristics of the strains by investigating the equi-displacement lines of fringes in weekly InSAR and double-differential InSAR (DDInSAR) images. The weekly InSAR images predominantly showed glacial shear strain of the fast ice with fringes parallel to the sides of the CGT. This was due to the cumulative flow of the CGT for a week, while oscillating tidal signals were relatively small. The DDInSAR images, which cancelled glacial strain rates in two one-day InSAR images, showed a deformation of the fast ice by tidal sea surface tilt, with the fringes parallel to the coastline. Based on the unique characteristics of these strains, we separated them from the one-day InSAR images by decomposing the fringe patterns into glacial and tidal strain. Glacial shear strain rates of fast ice attached to the east of the CGT decreased from May to August owing to ice thickening and then stabilized until December. Those to the west of the CGT increased from May to July. This was possibly due to bottom melting of the ice by the increased ocean circulation during the expansion period of the nearby polynya. The glacial strain then decreased until December because of reduced polynya activity. The fast ice near the Jang Bogo Station (JBS) only showed tidal strain as it was isolated from the CGT by cracks and leads. Tidal strain rates of the fast ice were strongly correlated with the magnitude of tidal variations in all these regions, which represents shows that the tidal strain represents tidal sea surface tilt. The tidal response of fast ice to the west of the CGT and near the JBS was stronger than that to the east of the CGT, probably owing to thinner ice thickness there.

Accurate measurement of ice-flow velocity of floating glaciers is required to estimate ice mass balance from volume flux thinning/thickening, basal melting/freezing, and surface accumulation/ablation. We derived a tide-corrected ice velocity map and mass budget of Campbell Glacier Tongue (CGT) in East Antarctica by using 14 COSMO-SkyMed one-day tandem differential interferometric SAR (DInSAR) pairs obtained from January to November 2011. The vertical tidal deflection of CGT was estimated and removed from the DInSAR images by using a tide deflection ratio map generated by double-differential InSAR (DDInSAR) method. We then generated averaged ice-flow velocity (v map) and its standard deviation (σv map). Ice-flow velocity increased from the upper part of the grounding line (~ 0.20 m d− 1) to the seaward edge of CGT (~ 0.67 m d− 1) with σv less than ~ 0.04 m d− 1 in the main stream of CGT. The eastern part of CGT flows slower than the western part because it is grounded along the flow line and thus experiences severe basal drag. Flux mass balance (FMB), i.e., ice thickness change by volume flux divergence, of CGT was obtained by combining the v map and an ice thickness value of 340 ± 18 m estimated by the ICESat GLAS data. We used mass conservation assumption in which total mass balance (TMB, − 6.29 ± 1.37 m a− 1 observed by ICESat GLAS data) is attributed to FMB, basal mass balance (BMB) and surface mass balance (SMB, 0.24 ± 0.02 m a− 1). Mass loss in the freely floating zone of CGT is mainly caused by basal melting (BMB = − 144.5 ± 39.9 Mt a− 1) while thinning by volume flux (FMB = − 67.2 ± 8.9 Mt a− 1) is relatively small. In the hinge zone of CGT, mass change is contributed to FMB of − 147.3 ± 25.2 Mt a− 1 and BMB of 15.3 ± 39.8 Mt a− 1. However, basal freezing derived for the hinge zone may be erroneous as a result of the constant ice thickness assumption extrapolated from the freely floating zone.

A glacier tongue, the terminus of a glacier projecting out from the coastline and floating over the ocean, experiences vertical deflection due to the fluctuation of ocean tide. Accurate analysis of the tidal deflection of a glacier tongue is necessary to understand the elastic properties and dynamics of glacial ice. We extracted the tidal deflection of Campbell Glacier Tongue (CGT), one of the fast-flowing glacier tongues in East Antarctica, by using 120 Double-Differential Interferometric SAR (DDInSAR) images from the 16 COSMO-SkyMed one-day tandem interferometric SAR image pairs obtained during 2010 and 2011. A map of tide deflection ratio ( α -map), defined as the ratio of the tidal deflection over tide height, was generated by pixel-based linear regression between the DDInSAR-derived tidal deflection and the tidal variation predicted by various tide models such as TPXO7.1, FES2004, CATS2008a and Ross_Inv after the inverse barometer effect correction. We also generated the maps of R 2 , root mean square error (RMSE), and intercept ( β ) of the linear regression model. We confirmed that the horizontal flow of the Campbell Glacier is steady over the whole data acquisition period due to the fact that α values were close to zero over the grounded part of the glacier. Ross_Inv provided the most reliable α -map with the highest R 2 (0.97) and the smallest RMSE (0.3 cm) beyond the hinge zone than other tide models. The spatial variation of the tidal response of the whole CGT was clearly defined from the α -map. The grounding line retreated by 0.3–1.5 km in comparison with that in 1996 defined by Rignot et al., 2011a. The ice thickness of CGT was estimated to be 397 ± 71 m from ICESat surface elevation data. The Young's modulus of CGT was found to be 0.5–1.3 GPa (0.8 GPa at an ice thickness of 397 m) by simulating the α in the hinge zone using a 2-dimensional finite element method.

a b s t r a c t Accurate monitoring of irrigated paddy field area and irrigation timing are of a great concern in agri- cultural water management due to the substantial consumption of fresh water when irrigating paddy fields. Spectral threshold methods (Xiao et al., 2005) have been widely applied to detect irrigated paddy fields and irrigation timing using Moderate Resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index (EVI) and Land Surface Water Index (LSWI). These methods applied constant additive threshold values (T) to LSWI and compared it to EVI to detect the irrigated paddy fields. In this study, we developed Variable Threshold Models that utilized different pixel-based threshold values depend- ing on sub-pixel land cover heterogeneity and hence, improve detection performance on distributed small-scale paddy fields. Non-irrigated sub-pixels were quantified with irrigation maps produced by Synthetic Aperture Radar (SAR) microwave images. Significant positive correlation between EVI and the sub-pixel numbers of non-irrigated area were found (r = 0.87), which resulted in higher T for MODIS pix- els with more non-irrigated sub-pixels. Accordingly, a Variable Threshold Model, i.e. a regression model between T and EVI, was developed. With the Variable Threshold Model, agreement rates between MODIS and SAR-based irrigated small-scale paddy field classification doubled compared with that from a fixed threshold value. In comparison with field observations, the Variable Threshold Models showed a mean error of +0.9 days, an improvement over the mean error of +2.8 days from a fixed threshold model. Combined utilization of SAR and MODIS images provides a useful tool for developing a Variable Thresh- old Model that can enhance accurate monitoring of irrigation dates across heterogeneous paddy field