Advanced Polarimetric Stereo-Sar for Tsunami Debris Estimation and Disaster Mitigation

Debris estimation is one of the most important initial challenges after a disaster like the Great East Japan Earthquake and Tsunami. Reasonable estimates of the debris must be made available to decision makers as quickly as possible. Classical approaches to obtain this information are far from being optimal, usually relying on manual interpretation of optical imagery. We have developed a novel approach for the estimation of tsunami debris pile heights and volumes for improved emergency response. The method is based on a stereo-synthetic aperture radar (stereo-SAR) approach for very high-resolution airborne polarimetric SAR. An advanced gradient-based optical-flow estimation technique is applied for optimal image coregistration of the low-coherence non-interferometric data. Its suitability to combine multiresolution data allows generating stereo SAR data by combining two different sensors. Based on model-based decomposition of the PolSAR data, only the odd bounce scattering contributions are used to optimize echo time computation. In this paper, we propose the further development of the method by combining multiresolution data from i) air-/spaceborne SAR and spaceborne/spaceborne SAR with various illumination geometries. The proposed technique is validated using in situ data of real tsunami debris taken on a temporary debris management site in the tsunami affected area near Sendai city, Japan. The estimated height error is in the order of 0.7 m RMSE. The good quality of derived pile heights allows estimating debris volume with an RMSE of 2500 m³ corresponding to <10% of the total debris volume. Advantages of the proposed method are fast computation time, and robust height and volume estimation of debris piles without the need for pre-event data or auxiliary information like DEM, topographic maps or GCPs.