Investigation of the ground displacement in Saint Petersburg, Russia, using multipletrack differential synthetic aperture radar interferometry Abstract   Global sea level rise and local land subsidence might exacerbate the risk of flooding in coastal plains. Among other cities, this is also the case for the highlatitude city of St. Petersburg, which has long been threatened by flood events. To protect the urban area from storm surges, the Union of Soviet Socialist Republics (USSR) in 1978 approved the construction of the 25 km long Flood Prevention Facility Complex (FPFC), which was completed in 2011. The risk of flooding in the city area of St. Petersburg is amplified by the fact that large sections of the coastal area have been reclaimed from the sea. In this study, we investigate the temporal evolution of the ground displacement in St. Petersburg. To this end, we perform an extended analysis based on the application of a simplified version of the differential interferometric synthetic aperture radar technique, known as the minimum acceleration (MinA) approach. The MinA algorithm is a multisatellitemultitrack interferometric combination technique that allows working with multiple sets of SAR images. The method allowed generation of time series of twodimensional (2D) (i.e. EastWest and UpDown) deformation of the terrain by processing two sequences of Sentinel1AB (S1AB) SAR images acquired from 2016 to 2018, along the ascending and descending flight passes. The Small BAseline Subset (SBAS) algorithm was independently applied to the two sets of SAR data to generate the relevant LineOfSight (LOS)projected ground deformation time series. Subsequently, the LOSprojected deformation products were geocoded and jointly combined. The results indicate that the deformation in the city is predominantly vertical (i.e. it is subsiding) with a maximum subsidence rate of about 20 mmyear corresponding to the newly seareclaimed lands. Finally, the error budget of the retrieved 2D deformation time series has also been addressed.

Evaluation of the Trend of Deformation around the Kanto Region Estimated Using the Time Series of PALSAR2 Data In the Kanto region of Japan, a large quantity of natural gas is dissolved in brine. The largescale production of gas and iodine in the region has caused largescale land subsidence in the past. Therefore, continuous and accurate monitoring for subsidence using satellite remote sensing is essential to prevent extreme subsidence and ensure the safety of residences. This study focused on the small baseline subset (SBAS) method to assess ground deformation trends around the Kanto region. Data for the SBAS method was acquired by the Advanced Land Observing Satellite (ALOS)2 Phased Array type Lband Synthetic Aperture Radar (PALSAR)2 from 2015 to 2019. A comparison of our results with reference levelling data shows that the SBAS method underestimates displacement. We corrected our results using linear regression and determined the maximum displacement around the Kujyukuri area to be approximately 20 mmyear; the mean displacement rate for 2015xe2x80x932019 was xe2x88x927.9 xc2xb1 2.9 mmyear. These values exceed those obtained using past PALSAR observations owing to the horizontal displacement after the Great East Japan Earthquake of 2011. Moreover, fewer points were acquired, and the root meansquared error of each timeseries displacement value was larger in our results. Further analysis is needed to address these bias errors.