# First Results from Sentinel-1A InSAR over Australia: Application to the Perth Basin
## 5 Results
### Multi-Temporal Analysis  
Despite the short time period of observation (0.7 y), deformation rate-maps produced for the overlapping Sentinel-1A and TerraSAR-X datasets show comparable results (Figure 4A-C), and time series of the vertical displacements recorded by both satellites are within the error of those measured  
Figure 3: Results of two tests used to evaluate the effect of using ERA-I to correct topographically-correlated atmospheric errors in the InSAR datasets. Interferograms corrected using ERA-I and with an orbital ramp removed are on the x-axes. Interferograms with an orbital ramp removed only are on the y-axes. Each point corresponds to an interferogram, and the dashed line is a 1:1 correlation. (**A**,**B**) Interferogram standard deviation (mm); (**C**,**D**) \(R^{2}\) metric of the correlation between interferogram pixel elevation and displacement. A reduction in value indicates an improvement to the interferogram.  
using GPS (Figure 4D), placing further confidence in the InSAR measurements over the short observation period.  
Figure 4: Deformation rate-maps for (**A**) 11 consecutive Sentinel-1A interferograms covering 27 August 2015–17 May 2016 and (**B**) 21 consecutive TerraSAR-X interferograms spanning 29 August 2015–19 May 2016. Deformation measurements are relative to the reference shown in (A,B). Locations (a), (b) and (c1, c2, c3) show areas of displacements described in the text: (a) broad (>5 km wide) subsidence at up to 15 mm/y; (b) elongated regions of adjacent relative uplift and subsidence; and (c) localised (\(\sim\)2 km wide), rapid (greater than 20 mm/y) subsidence coincident with wetland areas. The dashed lines show the locations of the profiles drawn in Figure 5. (**C**) Zoomed in sections showing subsidence in three wetland areas: Lake Jandabup (c1 in (A)), Lake Gnangara (c2 in (A)) and Forrestdale Lake (c3 in (A)). Blue circles show approximate boundaries of each wetland. (**D**) Time-series of cumulative vertical displacement measured at continuous GPS station HIL1 relative to continuous GPS station PERT (locations labelled in (A,B)). GPS data are from the Nevada Geodetic Laboratory, and InSAR displacements are calculated using the method described in the text.  
From the deformation rate-maps, we identify features of the deformation field that are evident in both InSAR datasets, verifying the application of Sentinel-1A with independent evidence from TerraSAR-X and also providing more information about a greater spatial extent of the deformation field in the Perth Basin than has previously been given by repeat levelling or continuous GPS [1]. We classify the observed displacements into three categories according to the magnitude and spatial extent of the deformation [54; 77]. These are: (1) broad regions (\(>\)5 km wide) of low magnitude (up to 15 mm/y) relative subsidence (labelled (a) in Figure 4); (2) elongated regions of adjacent relative uplift and subsidence (rectangle labelled (b) in Figure 4); and (3) localised (\(\sim\)2 km wide) relative subsidence at rates of greater than 20 mm/y coincident with wetland areas (labelled (c1, c2, c3) in Figure 4).  
In addition to these displacements, we observe other phase patterns that do not correlate between datasets, suggesting they are likely due to remaining atmospheric noise (Figure 4A,B). This may arise due to differences between the time of the Sentinel-1A and TerraSAR-X acquisitions and the time of ERA-I model simulation or atmospheric turbulence that is not captured by the model parameters [60]. Most notably, in the northeastern part of the TerraSAR-X stack (Figure 4B), there is a positive signal, which we attribute to unmodelled residual atmospheric stratification across the Darling Scarp (to compare the atmospherically-corrected and uncorrected deformation rate-maps, see Figure S1).