## 1 Introduction
The displacements caused by the above processes are significantly greater than their calculation errors and they can be determined on the basis of a small number of images acquired at relatively short time intervals [15]. Displacement measurements in urban areas require precision on the order of millimeters and thus a significant number of publications focus on verifying the results of InSAR measurements with the use of classic in-situ methods. [PERSON] et al. [22] researched the possibility of employing PSI in the area of Amsterdam to monitor the changes in elevation differences along a new underground line. In their study, elevation differences proved consistent with ground truth (tachymetry) data within the range of standard deviation up to 3 mm/year. Precision on the order of millimeters was also obtained for the LOS (Line of Sight) displacement measurements performed with PSI in the area of Bucharest [23]. The displacements were compared with the displacement vectors obtained in the GNSS measurements along the vector consistent with the LOS direction. Ground surface displacement trends in the area of Bucharest were determined with the use of multi-temporal and multi-sensor InSAR. A detailed analysis of the accuracy of the InSAR method was carried out by [PERSON] et al. [24] in the area of Los Angeles by comparing vertical displacements determined by InSAR (SBAS approach), GPS and levelling methods. Standards deviations of the difference between SAR and LOS--projected levelling and LOS--projected GPS measurements were 4.3 mm and 5.6 mm, respectively. A completely different approach based on qualitative assessment was proposed by [PERSON] et al. [25] using the compliance of displacement direction test obtained from SAR (LOS projected along vertical direction) and leveling measurements. The compliance obtained in the area of Schiedam (The Netherlands) was 80% with a sample of 180 benchmarks. [PERSON] et al. [26] presented the results of ground deformation survey performed for the area of Bratislava (Slovakia), over a period of 24 years, with the use of several SAR platforms (ERS-1/2, Envisat, Radarsat-2, Sentinel-1A, TerraSAR-X). The publication also included a proposal to integrate results from the multi-sensor InSAR for the monitoring of engineering objects. [PERSON] et al. [27] performed a detailed comparison of building displacement velocities obtained using PSI with the displacements determined using precise levelling method for the area of Turku in Finland. The authors demonstrated the applicability of PSI in establishing building displacement trends with the use of data provided by the ERS and ENVISAT satellites. However, they also pointed to the problem of determining and identifying the PS accurately and the need to verify PS results with classic measurements. Displacements and velocities obtained with InSAR methods are also used in cause-effect models. [PERSON] et al. [28] developed a multi-scale analysis of building damage based on DInSAR data on densely urbanized areas of southwestern portion of the Netherlands including geo-lithological properties, building in-situ damage survey and building characteristic. In turn, [PERSON] et al. [20] presented the use of InSAR data to assess the risk of geological hazard in combination with tectonic movements, Quaternary sediment compaction, and groundwater extraction. The main aim of the study is to determine the ground surface displacements on the area of Wroclaw in the 1995-2019 period, the spatio-temporal analysis of deformation and to identify the main factors causing deformations. To determine the displacement, an advanced PSI technique was used to develop data from ERS-2, Envisat and Sentinel-1 sensors. This work is a continuation and development of research conducted in the area of the city. It provides the first results on the process of deformation in short time intervals based on the use of SAR technology. The obtained results verify the hypothesis on the linearity of displacements obtained from historical geodetic observations.