Abstract:
An infrastructure of three corner reflectors for Sentinel-1 was deployed at the National Laboratory for Civil Engineering campus, in Lisbon, Portugal, with the collaboration of the IDL, FCUL. The infrastructure is formed by two triangular trihedral reflectors (1 x 1 m) and by a third one following a model proposed by the team. The third reflector is formed by two rectangular trihedrals with the vertical axis in common, each of the individual reflectors is oriented towards the ascending and the descending passes of Sentinel-1. Additionally, a Global Navigation Satellite System (GNSS) antenna is permanently installed on the reflector’s axis.
This study presents the first precision assessment for displacements measured at the infrastructure using Persistent Scatterer Interferometry (PSI). The PSI processing was performed with SARPROZ software using 19 Sentinel-1A images acquired between October 2017 and May 2018. The reflectors’ displacements are being monitored through levelling and GNSS. Levelling is performed for all reflectors every two weeks. Nearby persistent scatterers are included in the levelling line. A second permanent GNSS antenna is installed on a building roof in the campus to be used as a reference. PSI double-differences were compared to levelling and GNSS ones, projected onto the sensor line-of-sight. Precisions of 1.1 mm and 1.6 mm were achieved for the triangular trihedral reflectors, while 1.2 mm and 1.5 mm were obtained for the rectangular trihedral ones. However, during March 2018, strong winds have damaged the structure on which the rectangular trihedral reflectors are installed. If the evaluation is performed considering only the dates before the failure or only the dates after the damage was fixed, precisions of 0.7 mm and 0.8 mm are obtained. These results suggest submillimetre precision might be possible to achieve. Processing a larger time series of images acquired after the damage fix will be needed to confirm.