Sentinel-1 Change Detection Analysis for Cyclone Damage Assessment in Urban Environments

Abstract

For disaster emergency response, timely information is critical and satellite data is a potential source for such information. High-resolution optical satellite images are often the most informative, but these are only available on cloud-free days. For some extreme weather disasters, like cyclones, access to cloud-free images is unlikely for days both before and after the main impact. In this situation, Synthetic Aperture Radar (SAR) data is a unique first source of information, as it works irrespective of weather and sunlight conditions. This paper shows, in the context of the cyclone Idai that hit Mozambique in March 2019, that Change Detection between pairs of SAR data is a perfect match with weather data, and therefore captures impact from the severe cyclone. For emergency operations, the filtering of Change Detections by external data on the location of houses prior to an event allows assessment of the impact on houses as opposed to impact on the surrounding natural environment. The free availability of SAR data from Sentinel-1, with further automated processing of it, means that this analysis is a cost-effective and quick potential first indication of cyclone destruction.

Coseismic Ground Displacement after the Mw6.2 Earthquake in NW Croatia Determined from Sentinel-1 and GNSS CORS Data

“…Throughout the phase information mapped on the interferograms, deformations due to large earthquakes can be detected and main faults revealed. Some of the studies mentioned in [2] use SAR interferometry (InSAR) to detect the displacement related to land subsidence [3], earthquakes ( [4][5][6]), highway deformation [7] and similar land displacements ( [8], anthropogenic deformation phenomenon [9,10]), or urban change ( [11,12]). It has also been proved by a recent study [13] that InSAR measurements produce noise, but the noise can be reduced without the loss of significant data information by applying the processing techniques.…”

Remote sensing of urban cyclone impact and resilience: Evidence from Idai

“…Full coverage of the city of Beira was available 21 days after the cyclone made landfall in Beira. According to Malmgren-Hansen et al (2020), the price of such a full tagging of a city like Beira lies in the order of US$20,000-30,000 in total labour costs. An example of the tagged data can be seen in Figure 1.…”

“…The method is not completely independent of these unwanted changes but drastically reduces their influence on the results. The manually tagged damage is also filtered with a 1metre radius to an OSM building footprint Malmgren-Hansen et al (2020).…”

“…Manual tags and SAR changes have a spearman rank correlation of 0.55, and a Pearson correlation of 0.54 after square root transformation, corresponding to an explained variance score R 2 = 0.29 (Malmgren-Hansen et al 2020). This must be considered a low R 2 and shows that the manual tags and radar-detected changes are two different sources of information on the cyclone's impact.…”

“…In order to test the degree to which net cyclone impact is determined by pre-existing neighbourhood resilience, we merge data on initial wealth and building quantity and quality generated by Sohnesen et al (2019) with that of cyclone damage developed by Malmgren-Hansen et al (2020).…”