NGI has recently demonstrated a new exciting capability that extends an existing remote sensing technique into new territory. The technique uses large stacks of satellite radar imagery of exactly the same location on the Earth to map and track slow rates of subsidence.

The result in Figure 1 is a typical output of what is known as the Short Baseline Subset (SBAS) technique, based on papers by Berardino et al. (2002) and Lanari et al. (2004). The figure shows average deformation from 2003-2009 of the Swadlincote and Coalville area of central England through an analysis of radar data from the ENVISAT satellite. The deformation is displayed as a series of colour-coded dots, superimposed on a Google Earth map. There are some areas of blue which indicate uplift of more than 5mm/year, which may be linked to the recovery of former coal mines. Of particular concern are that, in this area, the dots are sparse and only appear where there is a good density of buildings, such as the towns of Swadlincote, Ashby-de-la-Zouch and Coalville. This is currently a major limitation of the technique.

Figure 1. A standard SBAS result of the Swadlincote/Coalville area

NGI researchers have extended the SBAS analysis and significantly increased the density of the points so that most of the rural areas can also be studied, too. The result from the extended SBAS method for the same area is shown in Figure 2. 

Figure 2. The extended SBAS result of the same area

As is clear, the uplift areas are now much larger and more continuous. The results have been compared with the geology by scientists at the British Geological Survey (BGS) in Keyworth (see Figure 3) and there is a much clearer correlation of the uplift with the coal measures than in the previous result.

Figure 3. The new results overlaid on the geology (Geological map copyright NERC 2012. All rights reserved.).

Although preliminary, this is an exciting result. It shows a great potential to bring studies of land deformation away from the cities and into rural areas and has enormous potential in applications such as mining, underground gas storage and the effect of groundwater pumping for agricultural and manufacturing purposes.

A number of papers on the above are in preparation. For further information please contact Andy Sowter.