# First Results from Sentinel-1A InSAR over Australia: Application to the Perth Basin
## 7 Conclusions  
Previous ground-based geodetic surveys have revealed subsidence at discrete points or along traverses in parts of the Perth Basin, but these measurements are spatially limited and sample only a small part of the metropolitan area. We have therefore carried out an investigation into the broader extent of the deformation field by performing the first application of Sentinel-1A InSAR data to Australia from published literature to date. Whilst the observation period is short (0.7 y), verification of Sentinel-1A with independent TerraSAR-X and continuous GPS (a) demonstrates close agreement between the vertical displacement fields measured with each satellite, acknowledging the effects of unmodelled atmospheric noise; and (b) provides new insights into the broader deformation field of the Perth Basin that can be used to guide subsequent targeted studies.  
With both Sentinel-1A and TerraSAR-X, we observe broad regions (>5 km wide) of small-magnitude (up to 15 mm/y) relative subsidence at Hillarys, through the agricultural Swan Valley and a region south of Fremantle. Other displacements are observed in elongated zones of adjacent relative uplift and subsidence south of Hillarys, and regions of relative subsidence at higher rates (greater than 20 mm/y), but on a smaller scales (\(\sim\)2 km wide), are found to be coincident with wetland areas. At these wetlands, time series of cumulative ground displacements are further verified by measurements of hydraulic head in the unconfined aquifer.  
Overall, these observations demonstrate the ability of Sentinel-1A to detect small-magnitude deformation over different spatial scales (from 2 km-10 s of km) in the Perth Basin. However, ongoing acquisitions of Sentinel-1B data are key to better characterising seasonal and long-term deformation rates. These measurements may provide useful constraints upon the hydromechanical structure of the Perth Basin aquifer system, which supports wetlands, agriculture, industry and a population of over two million people [85].  
The following are available online at www.mdpi.com/2072-4292/9/3/299/s1, Figure S1: Comparison between deformation rate-maps where atmospheric errors have not been corrected (left column) and where atmospheric errors have been reduced using ERA-1 (right column).  
This research was supported under Australian Research Council's Linkage Projects funding scheme (Project LP140100155), Landgate (the Western Australian geodetic agency), Curtin University and the Western Australian Department of Water. The views expressed herein are those of the authors and are not necessarily those of these organisations. We thank the German Aerospace Center (DLR) for supplying TerraSAR-X data under science project LAN1499 in association with Geoscience Australia, the European Space Agency for providing open access to Sentinel-1A data via the Sentinies Science Hub ([[http://scihub.copernicus.eu](http://scihub.copernicus.eu)]([http://scihub.copernicus.eu](http://scihub.copernicus.eu))) and JPL/Caltech for providing open access to the ISCE software via WInSAR (the Western North American Interferometric Synthetic Aperture Radar Consortium). We also thank the Western Australian Department of Water for providing the groundwater data and guidance on its usage, plus the editor and three anonymous reviewers for providing comments that helped to clarify the results of this study.  
All authors participated in editing and reviewing the manuscript. [PERSON] processed and analysed the InSAR datasets.  
The authors declare no conflict of interest.