The portal shows SatSense ground movement data as coloured points overlain on a map or aerial imagery. This data is our velocity product, which represents the average ground movement rate over the measurement period, typically mid to end 2015 to present. Red colours represent movement away from the satellite, typically subsidence, and blue movement towards the satellite, typically heave.
At zoom level 15 or above, you will be viewing point data, showing variations in ground movements over small areas. Although the data is plotted as points, each measurement point represents the weighted average of the radar return from all objects within a 4 by 20 meter area, the pixel size of the radar image. The data should therefore be interpreted at for example house level, but not corner of house level. For a large commercial building, variations within buildings are possible to detect.
At zoom level 14 or below, you're seeing so-called tiles, which are lower resolution resampled versions of the data. These show larger scale overview of the ground movements, allowing you to look at wider areas, but not showing as much detail.
Although SatSense data is available throughout the UK, looking at the map you'll notice some areas are better covered than others. The InSAR technique, which forms the basis for the SatSense ground movement data, relies on consistent reflections from the ground towards the satellite.
Buildings, structures, bare ground and other stable objects form such consistent reflections, while forests, agricultural land and other heavily vegetated areas typically do not. You'll therefore find that cities, are densely covered by measurements, while in more rural areas the coverage is often more limited to buildings, large roads and bare ground.
Our algorithms are designed to maximise the coverage, while not including points which do not hold usable information due to the physical effects of inconsistent reflections.
Whilst viewing point data (zoom level 15 or higher), you will be able to select points to see their time history graph by clicking on them. You can also select multiple points by using the polygon, rectangle or circle selection tools, located in the top left of the map, below the + and - zoom buttons. When using these selection tools, all points within the shape will be selected (with a limit of up to 20 points).
To allow comparison between the time histories of different points, any points that are selected will remain selected after closing the time series window. You can deselect individual points by re-clicking the point, or you can deselect everything by using the bin button in the top left corner.
When you select a point, the time history graph for this point will appear. The time history graph shows the ground movement in mm against time, and the graph pixels are colour coded to distinguish between points.
The time history graph reveals variations in the ground movements over time, information not contained in the long term average movement rate, which is the slope of the straight line through the time history points. It can show seasonal processes, event type movements, and changes in long term movement rates.