ИСТИНА

Many coastal cities are subject to severe natural and anthropogenic disasters such as flooding, storm surges and land subsidence. St. Petersburg is a coastal city with mostly flat topography and elevation ranges between around 1–2 m above the sea level. The city is situated on the shores of the Neva River, at the head of the Gulf of Finland in the Baltic Sea. Therefore, flood risks are a major concern and monitoring surface deformation in St. Petersburg is crucial for planning and reducing disaster risks. Interferometric Synthetic Aperture Radar (InSAR) measurement has the potential to enhance the information available from conventional surveying techniques and increases spatial and temporal coverage at low cost, with potential for ongoing monitoring. InSAR is the most suitable technique for detecting and mapping subsidence of various types of urban areas. The technique has actively developed in using remote sensing data and there are several methods of interferometric processing. These include classical differential interferometry (DInSAR) and serial interferometric methods. The rapid increase of the open radar data amount after the launch of Sentinel-1 satellites suggests the relevance of the research. Its aim was to develop methods for detecting displacements of the earth's surface in cities to secure safe life of a large number of people. The research presents the results of a new monitoring technique based on the method of radar satellite interferometry using open data from the Sentinel-1 radar satellite. The method of multitemporal DInSAR was chosen from the existing methods of satellite radar interferometry for determining the subsidence of the earth's surface in urban areas. This method was applied to St. Petersburg and was based on the Sentenel-1 data received from June 2018 to May 2019. Specified requirements were produced to create subsidence maps using 41 images downloaded for the selected monitoring period. Radar image processing was implemented on SNAP, open source software. As a result, 40 maps of vertical displacements of St. Petersburg were generated. Based on the QGIS geographic information software an analysis and visualization of the results of interferometric processing were performed. Thus, it was possible to identify the systematic subsidence of the soil due to the breakthrough of underground utilities in the Frunze district of St. Petersburg, which caused the accident. An insignificant decrease in soil subsidence was observed over the course of a month. The maximum value recorded by satellite data was 25 cm. The emergency situation that occurred in the time interval corresponding to the monitoring confirms the subsidence detected as a result of interferometric processing. The proposed procedure allows continuous monitoring of land subsidence based on open SAR data and open software. In the future, this method can be used to monitor displacements of the surface and prevent emergencies in urban areas.