## Materials and Methods  
This study uses Sentinel 1a C-band SAR data to produce a time-series of interferograms used in the PSI process. Sentinel-1 Single Look Complex (SLC) data has a swath width of 250 km in Interferometric Wide (IW) mode, with a spatial resolution (pixel size) of 3 m \(\times\) 20 m in range and azimuth, respectively. The tandem satellites (Sentinel 1a and 1b) cycle over 175 different orbits and have a full-global repeat cycle of 6 days. Many areas--such as the UK--receive more frequent data acquisition. Sentinel 1 images were selected based on the same orbit number to ensure full spatial coverage of the study areas. Precision orbit ephemerides files were downloaded for each SAR image to ensure that no errors occurred in the co-registration of the data. This process, known as de-bursting, ensures phase continuity over the burst limits. If no precise orbit files are applied, then linear features can appear in some interferograms [15]. Images were also selected as per the minimum separation between two orbits for each pair (perpendicular baseline) at an interval of at least 12 days, so limiting the temporal and spatial decorrelation of the interferometric pairs. Data were collected in two separate areas (see Figure 1) so comparison between infrastructure responses over a large area could be undertaken. For the Western study area (Bristol, Bath and Bournemouth), data were downloaded between the 8 September 2015 to the 31 December 2016, with a polarization of VV (Vertical transmit and Vertical receive) in ascending orbit. In total, 23 images were downloaded for processing, including one master image which was selected as the 16 July 2016. For the Eastern study area (Grantham, Peterborough and Kings Lynn), 23 images were collected from the 13 January 2016 to the 8 March 2017, also collected in VV polarisation in ascending orbit. The master image for all Eastern England sites was selected as the 16 August 2016. See Table 1 for a description of the image dates, perpendicular and temporal baselines of the Sentinel 1a images used in this study. All PSI processing was conducted using Harris Corporation's (Melbourne, FL, USA) ENVI SARscape software v5.3. After the SAR images were connected (spatially and temporally), a series of interferometric pairs were created. These image pairs were then consequently co-registered to the master images' slant geometry. Each of the slave images were then co-registered to the master to calculate the phase difference between each image pair. A Doppler filter was applied to reduce the temporal decorrelation of the image pairs. In this step, a SRTM 3 Digital Elevation Model (DEM) was downloaded with a spatial resolution of 90 m to correct errors related to phase and atmospheric effects between the interferometric pairs. For each study site Ground Control Point (GCP) files were created to correct the images geometrically, after which a Goldstein filter was applied to decrease the signal-to-noise ratio by filtering the differential phase [23]. Values of 5 in range and 1 in azimuth were used in the multi-looking phase to obtain square pixels for the image pairs. This step is used to avoid the effects of over and under sampling on geocoded images. Figure 1: Study area extents shown with major soil group and infrastructure extent. Western sites—shown in red—include: (1) Bristol; (2) Bath; (3) Bournemouth. Eastern sites—shown in blue—include: (4) Grantham; (5) Kings Lynn; (6) Peterborough. The insert map locates the sites within the UK. Dashed red and blue outlines represent the area extent of the Sentinel 1 data frames (Western England—relative orbit number 30, Eastern England—relative orbit number 132). The locations of Meldon Quarry validation test site, Tadham Moor, and Redmere meteorological stations, have been shown in the insert map. The interferometric pairs were then processed by the first and second inversion steps in the ENVI PSI workflow to locate the potential Persistent Scatterers (PS).