Development of cost-effective passive corner reflectors using low-cost materials for SAR and InSAR applications

Corner reflectors (CRs) are artificial installations at specific locations that reflect radar or other electromagnetic waves toward their emission source. There are two types of corner reflector: passive CRs lack electronics, while active CRs have electronics to amplify the reflected signals. CRs have a high and stable radar cross section, a well-defined scattering centre, and are easily detectable in the image, making them suitable for SAR radiometric, geometric, and polarimetric calibration. CRs are also used for SAR interferometry (InSAR) applications over areas with few natural coherent scatterers, and for InSAR datum connection and geodetic integration. Passive CRs are often made of metal plates, such as aluminium. Drawbacks of using metal CRs include (i) their high cost, especially when many reflectors are required for monitoring purposes; (ii) creation of localized ground motion in soft or unstable soils and (iii) attractiveness for thieves. The main objective of this study is to investigate the use of low-cost and lightweight materials for making CRs. A cubic trihedral CR, made of 2mm thick aluminium plates, served as a baseline for our analysis.  It was compared to CRs built either from (a) 10mm thick multiwall polycarbonate sheets covered by 1mm thick aluminium foil tape, or from (b) multiwall polycarbonate sheets coated with metallic paint. In addition, the microstructure of these materials was analysed by using scanning electron microscope (SEM) technique in a laboratory. To assess the SAR reflectivity of the different CRs they were temporarily installed at a test site and their visibility and backscattering properties were assessed in Sentinel-1 images. Furthermore, two CRs were installed in a landslide to investigate their performance in a real InSAR application. The study revealed that low-cost materials can deliver performance levels comparable to metal materials, in terms of visibility and backscattering properties, while reducing the weight and cost.