Ground-based radar interferometry for landslides monitoring: atmospheric and instrumental decorrelation sources on experimental data

The application of ground-based radar interferometry for landslide monitoring is here analyzed: a case study based on an experimental campaign carried out in Italy in the year 2002 is discussed. Interferometric data obtained from coherent synthetic aperture radar (SAR) images acquired by means of C-band ground-based equipment are analyzed. The campaign was aimed at retrieving potential terrain movements of a small landslide observed hundreds of meters away. Critical aspects related to spatial and temporal decorrelation are discussed: the use of optical photogrammetry as a technique for evaluating mechanical stability and correcting geometric distortion is presented. A custom setup with optical targets fixed on the ground has been built around the radar in order to monitor antennas positioning and orientation respect to the landslide. An off-the shelf Nikon camera has been used and calibrated in the lab for taking into account its own optical distortions (radial, tangential and affine). Multi-image bundle adjustment has been used for increasing redundancy and lowering measurement uncertainty. A final post-processing for identifying the most probable outliers has been implemented, in order to take into account the error statistics for optimizing the final result. Results also confirmed that the application of ground-based radar interferometry can be attractive and effective if the acquired SAR images maintain an adequate coherence on different dates.