Abstract
Abstract. The identification of changes in urban settlements is of great interest for damage assessment after natural disasters, cadastral mapping and monitoring urban development and illegal activities.Radar-based remote sensing from space-borne platforms is quite useful in this scenario and Synthetic Aperture Radar (SAR) data is attractive due to its wide coverage, the day and night all-weather availability, and the sensitivity to slight changes in the scene structure. In this context, the launch of the European Space Agency (ESA) constellation Sentinel-1 has played a significant role: the exact repetition of the acquisition geometry, the repeated illumination and the sensitivity to centimetric changes thanks to the C-Band (5.4GHz) radar payload make Sentinel-1 the perfect instrument to monitor urban settlements.Coherent Change Detection (CCD) techniques are able to detect even the finest change in the structure of a target, so small to be comparable with the wavelength. This sensibility is an advantage, but turns into a drawback especially in an urban environment where every subtle change may cause an unwanted detection.This paper tackles the problem of the huge amount of triggered detections over urbanized areas with a combination of a high-resolution coherent multi-change detection technique and Geospatial Information System (GIS) post-processing. The final result is a map of buildings that are changed in the scene due to relevant variation of their structure. In this contribution, the complete workflow is explained, and a preliminary validation is carried out by means of a set of images gathered by Sentinel-1 and a set of optical images over the city of Manchester.
Highlights
The ansence of cloud coverage, the possibility to sense the scene night and day, the repeated geometry of acquisition and, the most important, the high sensitivity to fine changes in the spatial structure of the scene are all peculiarity that contribute to Synthetic Aperture Radar (SAR) images very popular for change detection purposes
The main challenge of any SAR coherent change detector is to discard a huge number of unwanted detections both in space and time
The former is due to subtle and uninteresting changes in the structure of a target while the latter is due to the temporal instability shown by the urban environment when long time series are used
Summary
The ansence of cloud coverage, the possibility to sense the scene night and day, the repeated geometry of acquisition and, the most important, the high sensitivity to fine changes in the spatial structure of the scene are all peculiarity that contribute to SAR images very popular for change detection purposes. Coherent change detection (CCD), exploits the phase information of the back-scattering process leading to a much higher sensitivity even to fine changes (in the order of a fraction of a wavelength) (Preiss and Stacy, 2011, Mian et al, 2019, Wahl et al, 2016). This sensibility is so high that a huge number of changes can be triggered due to slight variations of features that are not of interest: these nuisance detections can hinder the recognition of interesting changes. The entire processing workflow is validated with a case study over the city of Manchester, UK
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