Detection of damaged urban areas using interferometric SAR coherence change with PALSAR-2 4. Seismology

The interferometric SAR coherence-change technique with coherence filter and polarization (HH and HV) has been used to detect the parts of buildings damaged by the 2015 Gorkha Earthquake. A survey of the building damage was conducted in every house to evaluate the detection accuracy in the Khokana and Sankhu urban areas in the Kathmandu Valley of Nepal. The damaged parts of the urban area were adequately detected using coherence-change (δγ) values obtained before the earthquake (γ _pre) and during the inter-seismic stage of the earthquake (γ _int). The use of a coherence filter effectively increased overall accuracy by ∼2.1 to 7.0 % with HH polarization. The incorporation of HV polarization marginally increased the accuracy (∼0.9 to 1.2 %). It was confirmed that road damage due to liquefaction was also observed using the interferometric SAR coherence-change detection technique. The classification accuracy was lower (27.1-35.1 %) for areas that were damaged. However, higher accuracy (97.8-99.2 %) was achieved for areas that were damage-free, in δγ obtained from HH and HV polarization with a coherence filter. This helped to identify the damaged urban areas (using this technique) immediately after occurrence of an earthquake event.