Coherence optimisation and its limitations for deformation monitoring in agricultural regions

Differential interferometry techniques are well known for their ability to provide cm to mm scale deformation measurements. However, in natural and agricultural areas, the presence of vegetation and the evolution of the land surface introduce a phase noise component which limits successful interferometric measurement. In underground mining environments, operational monitoring of surface deformation will be limited due to these temporal decorrelation effects. This paper aims to address the known limitations of traditional dInSAR in the presence of disturbances to reflected signals due to agricultural activities by testing the polInSAR technique for its ability to increase interferometric coherence and to detect surface movement in the areas of interest. Both fully polarimetric RADARSAT-2 and ALOS PALSAR data were subject to coherence optimisation using the Multiple Scattering Mechanism approach. For C-band RADARSAT-2 data, coherence optimisation resulted in a statistically significant increase in interferometric coherence. However, the spatial heterogeneity of the scattering process and how it changes over time caused random phase changes associated with temporal baseline effects and the evolution of the land surface. These effects could not be removed from C-band interferograms using the polInSAR approaches. Therefore, coherence optimization resulted in an increase in the random speckle in interferograms reducing the ability to derive high confidence interferometric measurements. On the other hand, coherence optimization on L-band data demonstrated an increase in the spatial homogeneity of the speckle noise indicating that coherence optimization on L-band data may be more successful in enhancing the ability to extract deformation measurements in dynamic agricultural regions.