Time-series radar interferometry for monitoring ground deformation
Delft University of Technology
Department of Earth and Atmospheric Sciences
Over the last two decades, spaceborne Interferometric Synthetic Aperture Radar (InSAR) has been successfully applied over several regions of the world for millimetric measurements of ground deformation occurring at radar scatterers that are phase-coherent over a period of time (persistent scatterers or PS). In my seminar talk, I will begin with a brief overview of the concepts of differential InSAR, time-series InSAR, and their error sources. As an example, I will touch upon the case of mining deformation in Kiruna, and will subsequently deal with the following aspects of my research.
An important consideration of time-series InSAR is that the availability and distribution of PS may be suboptimal for monitoring a particular deformation phenomenon, especially in non-urbanised areas. Furthermore, InSAR being â€™opportunisticâ€™, a PS may not be available precisely at the location where monitoring is desired, such as on a particular building. Artificial PS may therefore need to be introduced, the simplest of these being corner reflectors. However, they are large (in the order of a metre for C-band SAR) and cumbersome. To make these artificial PS easy to deploy and maintain, especially in poorly accessible areas, active radar transponders have been designed to be used instead of corner reflectors. Being active, they can be much more compact (a few tens of centimetres) and lightweight (<3 kg). Additionally, unlike reflectors, a single transponder setup may be used for multiple satellite tracks and modes.
A second noteworthy aspect is that InSAR observations are relative double differences; height changes are relative to a reference point and time. If the selected reference point (PS) is not stable, the deformation measurement will be erroneous. It is therefore desirable to measure the absolute deformation at an InSAR reference point. A compact solution at such a reference point would be an integrated unit consisting of a radar transponder and a GNSS receiver on a common baseplate, with precise phase-centre offset estimation and accurate attitude control.
A prototype of such a unit, called I2GPS (Integrated Interferometry and GNSS for Precision Survey) has been developed.
For millimetre-level subsidence monitoring, it is of paramount importance to ensure that the phase of the radar transponder remains stable in the relevant operating and environmental conditions. This, and the functioning of the combined I2GPS devices have been tested at a calibration site in Delft, and a precision limit for their use in deformation monitoring has been calculated using ERS-2 radar data. Results from this experiment will be presented and discussed.
Created 2012-01-18 14:24:17 by Uwe Raffalski Last changed 2012-03-20 15:10:34 by Uwe Raffalski