This exciting project aims to improve the accuracy of deformation measurements made from Space and apply this to improve our understanding of where earthquakes will occur. Measurements of displacement from multiple other causes will also be improved.
Radar Interferometry (InSAR) is a technique that provides measurements of surface displacement from Space, potentially with millimetric accuracy. These measurements are used in the natural hazards community for earthquake analysis and monitoring of volcanoes and landslides, as well as for monitoring of anthropogenic activities such as oil and gas extraction and drawdown of underground water storage.
An ongoing recent effort of the COMET Centre of Excellence, led from Leeds, is to use long time series of regular radar acquisitions to measure tectonic strain rates with sufficient accuracy to improve earthquake hazard maps. Since 1900, between 1.4 and 1.7 million people have been killed by earthquakes in continental interiors. In contrast to the narrow boundaries on the edges of oceanic plates, continental seismic belts span broad regions and earthquakes often occur on unidentified faults. Although most earthquakes appear to have no recognisable short-term precursor, all are preceded by a long, slow build-up of strain around the causative faults and maps of tectonic strain can therefore inform models of seismic hazard.
In order to achieve millimetric accuracy there are several noise terms that need to be reduced. The most significant of these is the variability in signal propagation through the atmosphere, and much effort has been put into estimating and reducing this noise source. Although the effects cannot be completely ameliorated, the impact can be further reduced by building long time series of images. However, a further noise source, which has mostly been ignored in the past, comes from changes in the scattering properties of the ground due to changes in moisture content and vegetation. This effect was previously assumed to average out over time, but it has been shown recently that this noise source can accumulate systematically when long times series are built from interferograms of shorter length, which is typical of the so-called “small baseline” approach usually adopted outside of urban areas.
The soil moisture/vegetation effect can be isolated by forming and comparing deformation maps from images acquired on three different dates: the deformation map formed the first and third dates is compared to the sum of the deformation maps formed from the first and second dates and the second and third dates. The difference between the two is termed the “closure phase” and will be non-zero if there is a systematic effect of soil moisture and/or vegetation change.
In this project the student will develop ways to estimate and reduce the systematic effect of moisture and vegetation in time series of images, and apply these methods to improve maps of tectonic strain rates, leading to better estimation of global earthquake hazard. The methods developed in this project will also be used to improve times series of deformation related to anthropogenic causes.