Experimental Study of the Stability of a Low-Cost C-Band Active Reflector Using Sentinel-1 Imagery

The application of Synthetic Aperture Radar (SAR) interferometry (InSAR) techniques when in the imaged areas the coherence is low and persistent scatterers are missing often demands the installation of artificial reflectors, usually represented by passive corner reflectors (PCR). For missions based on C band sensors such as Sentinel-1, passive corner reflectors capable of providing a high phase accuracy are cumbersome and heavy, and their installation in hard places can be difficult and costly. The installation of active reflectors, compact and smaller with respect to passive corner reflectors, can sometimes represent a valid alternative but the use of these devices has not yet largely spread due to their high sensitivity to the seasonal temperature variation which can reduce their reliability both in amplitude and phase stability. This paper focuses on the analysis of the performance of a low-cost active reflector designed to operate with C band spaceborne radars, tested in a real field campaign using Sentinel-1 imagery. The goal is to assess through an experimental based approach the stability of this device, using data acquired during the monitoring campaign of a landslide based on InSAR. The stability of the Active Reflector (AR) installed in a stable area is analyzed to evaluate its performance when used as a reference in interferometric processing. The results of this study show a stability over a temporal lapse of almost three years equivalent in deformation measurement to a few millimeters accuracy, which can be considered a satisfactory goal for this InSAR application.