Processing of the InSAR data has provided the first baseline assessment of land surface deformation covering a 25-year period in the Vale of Pickering, albeit with a gap in the coverage following the ENVISAT de-orbit and prior to Sentinel-1 launch. The results from the SBAS analysis comprises 47,930 ERS, 72,697 ENVISAT and 71,881 Sentinel-1A points which increase to 836,939 ERS, 234,793 ENVISAT and 637,753 Sentinel-1A points in the ISBAS results (Figure 41).
Table 14. Sentinel-1 image metadata (Lancashire) Satellite Time period No. of scenes in the stack Processing mode Processed by Max velocity (mm/yr) Min velocity (mm/yr)
Sentinel-1 (Asc) 2015-2019 ISBAS GVL +5.6 -7.03
Sentinel-1 (Desc)
2015-2019 177 ISBAS GVL +3.54 -7.97
Sentinel-1 (Asc) 2015-2019 178 Urban SatSense +28.36 -50.75
Sentinel-1 (Asc) 2015-2019 178 Rural SatSense +6.83 -34.59
Sentinel-1 (Desc) 2015-2019 164 Urban SatSense +26.78 -54.56 Sentinel-1 (Desc) 2015-2019 164 Rural SatSense +18.59 -27.23 3.4.1 1992-2000 Baseline
75 ERS-1/2 SAR scenes for 1992-2000 are available along satellite track 366 in descending mode. Of the 75 ERS-1/2 scenes in the archive, three were not used due to missing lines within the data. The results of the ERS-1/2 InSAR analysis are shown in Figure 42. Green areas are considered stable, red are subsiding on average over the time period, and blue are undergoing uplift.
As expected, the SBAS results are primarily constrained to urban areas (including roads) as these provided coherence in all of the radar images in the stack. It is apparent that the area was predominantly stable between 1992 and 2000. There is a discrete zone of subsidence north of Whitby (in the Loftus area) but this is outside the Vale of Pickering monitoring area.
The ISBAS analysis of the ERS-1/2 radar data also indicates that the majority of the area was stable. There are three zones of ‘dispersed’ uplift in this analysis, to the west, southwest and south of Scarborough. We believe that these zones in the ISBAS analysis are not related to geological motion (in our experience geological motion is more discrete), but are most likely due to vegetation changes and agricultural practices.
Figure 41. ERS SBAS (a), ERS ISBAS (b) ENVISAT SBAS (c), ENVISAT ISBAS (d), Sentinel-1A SBAS (e) and Sentinel-1A ISBAS (f) results for the Vale of Pickering area, showing average rates of ground motion. Location of GNSS stations and InSAR
reference point are indicated with a triangle and star, respectively. From Ward et al. (2017).
Figure 42. InSAR SBAS (top) and ISBAS (bottom) analysis of ERS-1/2 satellite imagery (1992-2000) for the Vale of Pickering. Radar data supplied to BGS by ESA under grant id.31573. From Ward et al. (2017).
InSAR SBAS results 1992-2000
Vale of Pickering Study Area
Vale of Pickering average ground
motion velocity (mm/yr) -3.068000 - -2.500000 -2.499999 - -2.000000 -1.999999 - 2.000000 2.000001 - 2.500000 2.500001 - 3.307000
InSAR ISBAS results 1992-2000
Vale of Pickering Study Area
Vale of Pickering average ground
motion velocity (mm/yr) -4.416000 - -2.500000 -2.499999 - -2.000000 -1.999999 - 2.000000 2.000001 - 2.500000 2.500001 - 6.259000
Figure 43. InSAR SBAS (top) and ISBAS (bottom) analysis of ENVISAT satellite imagery (2002-2009) for the Vale of Pickering. From Ward et al. (2017).
InSAR SBAS results 2002-2009
Vale of Pickering Study Area
Vale of Pickering average ground
motion velocity (mm/yr)
-4.443000 - -2.500000 -2.499999 - -2.000000 -1.999999 - 2.000000 2.000001 - 2.500000 2.500001 - 5.816000
InSAR ISBAS results 2002-2009
Vale of Pickering Study Area
Vale of Pickering average ground
motion velocity (mm/yr)
-7.346000 - -2.500000 -2.499999 - -2.000000 -1.999999 - 2.000000 2.000001 - 2.500000 2.500001 - 9.324000
3.4.2 2015-2016 Baseline
Imagery acquired by the Sentinel-1A between 8th May 2015 to 30th August 2016 was acquired
and processed. The stack comprised 36 images. SBAS processing of the Sentinel-1A data resulted in an average point density of ∼17 SBAS points/km2. When the Sentinel-1A data was
processed with ISBAS the number of points increased by a factor of ∼8.3, providing a coverage of 89% (corresponding to ∼141 points/km2) with the highest increase in measurement density
observed in areas of non-irrigated arable land, pastures and natural grasslands (Figure 44). The additional coverage has not come at the sacrifice of quality with an average standard error of 1.93 mm/year. As expected, the coherent targets concentrate over the urban areas of Scarborough, Pickering and Malton where the highest values of the interferometric coherence were observed.
Figure 44. Average SBAS and ISBAS densities obtained for each land cover type from ERS, ENVISAT and Sentinel-1 results (CLC2012). From Ward et al. (2017).
The network of GNSS receiving stations from the NERC British Isles continuous GNSS facility (available at www.bigf.ac.uk) was used to validate the ISBAS time-series over two sites (Figure 45). The SCAR station (from 05/01/03 to 09/02/09) renamed to SCAO (from 20/02/09) and the YEAR station (from 24/05/04-22/01/09) then renamed to YEAS (from 16/04/09 to 10/03/16) time-series GNSS data were used to validate / constrain the magnitude and timing of ENVISAT and Sentinel-1A motion (Figure 46).
The displacements at the two GNSS stations, at rates of -0.54 mm/yr for SCAO-SCAR and - 0.56 mm/yr for YEAR-YEAS, are in agreement with the subsidence observed at the closest ISBAS points for the equivalent time span, confirming the validity of the InSAR results. Figure 45 illustrates the average annual ground motion derived from ISBAS results for the Pickering-Malton area. An area of uplift (of ~5mm/yr) is visible in the western sector of the valley, between Pickering and Malton, for the 2002-2009 time-span which almost doubles (to ~10mm/yr) for the 2014-2016 period and has been detected through intermittently coherent targets. The uplift is delimited both to the north and south to the presence of Quaternary lacustrine deposits of the Glacial Lake Pickering (Evans et al., 2016). There also appears some correspondence between uplift and east-west faults, identified as dashed lines in Figure 45.
Figure 45. Non-linear time series for selected ISBAS points. The solid lines represent the ISBAS non-linear vertical displacements for the different acquisitions and the dotted lines represent the GNSS linear and vertical displacements which were derived separately. It is worth noting that the InSAR time series reported were generated considering a linear displacement velocity in the temporal gaps between the ENVISAT and Sentinel-1A datasets. From Ward et al. (2017).
Figure 46. ISBAS InSAR results for the Pickering area of the Vale of York. Blue areas are undergoing uplift while green / yellow areas are stable. Dashed lines are geological faults. Solid black line is the trace of the section in Figure 47. Contains Ordnance Data © Crown Copyright and database rights 2019.
The spatial pattern of the Sentinel-1 ISBAS velocities reveals the occurrence of instability within the clay and silt sediments of the lacustrine deposit, which south of Kirby Misperton exceeds 20 m in thickness (Figure 47). Faults of the basement play a significant role in the heterogeneity of the uplift rates by identifying three main domains:
1. the northern area with average velocities ≥6mm/yr, 2. the central section with velocities ≤3mm/yr
3. southern portion with velocities ~5mm/yr.
Abrupt changes in the ground motion at the location of a fault (Figure 47) suggesting that the faults constrain the motion, possibly by their influence on the groundwater flow at depth.
Figure 47. ISBAS InSAR results for the Pickering are of the Vale of York across the section identified in Figure 46. From Ward et al. (2017).
A possible explanation for the observed uplift relates to the wet winter of 2015-2016. The Coralline Limestone to the North and South of the Vale of Pickering (Figure 48) may allow a groundwater flow, which recharges the aquifer at depth, thereby increasing the pressure. Alternatively, the uplift may relate to shallower processes; the increase in surface water (many members of the public at the engagement events suggested there was a great deal of surface flooding during the winter of 2015-16) may have led to a swelling of the glaciolacustrine clays (Figure 48), which are responsible for the flat topography of the Vale. The InSAR time series supports the notion that the uplift relates to the timing of a wet winter as we see an increase in uplift rates following the winter of 2015-2016 (Figure 49).
Figure 48. Bedrock geology and faults for the Pickering area of the Vale of York. Brown areas are clays from the quaternary glacial lake, green represents Chalk whilst the yellows and pinks to the North and South are the Coralline limestones and Calcareous Grits. From Ward et al. (2017).
Figure 49. ISBAS InSAR Time series for the Pickering (green) and Malton (blue) areas. From Ward et al. (2017).
3.5 LANCASHIRE GROUND MOTION BASELINE