SPATIAL-TEMPORARY CHANGES IN RADAR BACKSCATTERING OF BUILT-UP AREAS OF BAKHMUT AND UZHGOROD ACCORDING TO SENTINEL-1 DATA

Monitoring spatiotemporal transformations of urban areas is particularly important under conditions of intensive anthropogenic pressure and large-scale changes in the urban environment caused by military activities. Radar remote sensing provides an effective tool for detecting such transformations regardless of cloud cover and illumination conditions. This study assesses changes in radar backscatter from built-up areas of Bakhmut and Uzhhorod using Sentinel-1A data processed in the Google Earth Engine (GEE) environment. Built-up areas were identified using ESA WorldCover 2021. Median July composites of VV and VH backscatter were generated for 2021 and 2025, while the intervals 2018–2019, 2019–2020, and 2020–2021 were additionally analyzed to characterize background interannual variability. In 2021–2025, the proportion of built-up areas with strong radar backscatter changes (|ΔSAR| ≥ 5 dB) reached 21.80% in Bakhmut and 10.20% in Uzhhorod, compared with pre-war mean values of 6.27% and 4.88%, respectively. The most pronounced difference was observed for VV polarization. Strong VV backscatter reduction (ΔVV ≤ −5 dB) covered 11.58% of the built-up area in Bakhmut, compared with a pre-war mean of 1.45%, whereas in Uzhhorod it accounted for only 1.40%, close to the background level of 1.33%. In contrast, strong VV backscatter increase (ΔVV ≥ +5 dB) was more pronounced in Uzhhorod, reaching 5.11%, compared with 3.78% in Bakhmut. The results demonstrate substantial differences in both the magnitude and direction of radar backscatter changes between the two urban systems and confirm the potential of Sentinel-1 for detecting significant structural transformations of built-up areas. However, the physical causes of individual SAR anomalies require independent verification using optical satellite imagery or other reference data.