The impressive ability of the PAZ radar satellite to detect subtle changes in the stability of key transport infrastructure, including airport runways, bridges and railways, has been demonstrated using data delivered via ESA’s Third Party Mission’s (TPM) programme.

The study – which drew on Synthetic Aperture Radar (SAR) data collected over the Hambach region of Germany, between 2021 and 2022 – aimed to compare the performance of PAZ with Copernicus Sentinel-1 to assess its suitability for observing deformation or ground movement at urban scales. 

Owned and operated by Spanish satellite company Hisdesat, PAZ carries a highly precise X-band SAR sensor with several polarisation choices available. In contrast, Copernicus Sentinel-1 operates at the longer C-band wavelength with vertical-vertical (VV) polarisation, providing data at a lower resolution when compared to PAZ.

During the study – which was completed by Spain-based digital transformation services company Tracasa Global – an advanced remote sensing analysis technique, named persistent scatterer interferometry (PS-DInSAR), was used to estimate ground displacement.

This method focuses on analysing persistent scatter points, which are features or objects on Earth’s surface that consistently reflect radar signals, serving as precise markers for the tracking of displacement, subsidence or deformation.

Idurre Barinagarrementeria, remote sensing scientist at Tracasa Global, explained, “Many natural features, like soil or vegetation change quickly in response to weather conditions and other factors, meaning that their reflections are not consistent. However, certain structures or surfaces, such as railway tracks, road signs, and airport runways, remain unchanged and, therefore, provide relatively stable reflections that can be observed over time to assess ground movement. These features are known as persistent scatter points.

“The greater the number of persistent scatter points identified, the more precisely deformation can be monitored.” The project team inspected 50 PAZ radar images – provided via ESA’s TPM programme – with spatial resolutions of 3 metres to identify a range of transport infrastructure for PS-DInSAR analysis. In parallel, 88 radar images from Sentinel-1 with spatial resolutions of 12 metres, covering the same areas of interest, were analysed as a means of comparison.

Across the analysis, PAZ identified some 2.7 million persistent scatter points, far exceeding the 300,000 persistent scatter points observed by Sentinel-1. This was attributed to the higher spatial resolution of PAZ, which makes it more attuned to identifying small, stable features in high-density urban settings.

The results of the comparison between PAZ and Sentinel-1 showed that PAZ was particularly adept at identifying persistent scatter points on flat surfaces, such as airport runways or roads, which are vital for assessing deformation. Sentinel-1, on the other hand, was more suited to picking out vertical structures, such as buildings or towers.

Following the PS-DInSAR analysis, a correlation scatterplot was used to demonstrate the alignment of PAZ and Sentinel-1 data, indicating that both satellites can reliably estimate deformation. However, the higher number of persistent scatter points detected by PAZ mean that it is able to monitor deformation and stability with a greater level of precision.

Idurre Barinagarrementeria added, “Our study highlights the suitability of PAZ for monitoring the stability of transport infrastructure in dense urban settings.

“These findings underscore the potential of PAZ to redefine standards for ground displacement monitoring, providing a high level of detail and reliability for civil engineering, urban planning, and disaster risk management.”

Building on the current study, the project team now aims to explore the use of artificial intelligence techniques to identify persistent scatter points, as well as investigating the geological processes linked to ground displacement identified by PS-DInSAR.