Simple and robust quad-corner reflectors for persistent scatterer measurements

In Synthetic Aperture Radar image data, control point acquisition poses a major challenge, as object signatures can vary strongly depending on the incidence and aspect angle. The definition of suitable control points is essential and requires investigation of their backscatter variation. Since the choice of such control points is determined by the requirement to find stable and permanent points, man-made structures such as lamp posts or traffic sign systems seem to be the most reliable. However, in many cases, it is difficult to identify such targets of opportunity in an observed scene. In particular, for interferometric measurements, artificial corner reflectors can be used and positioned to provide controlled coherent targets. To minimize the effort for such measurements, it is important that the corner reflectors are suitable for ascending and descending orbits and cover as many different azimuth angles as possible. In this study, height-adjustable quad-corner reflectors (half-octahedral structure), designed by IOSB, are assessed with regard to their suitability as position reference and control points in the context of a persistent scatterer measurements. In a measurement campaign variation in reflector alignment were simulated using a circular arrangement of a corner group. A total of 17 corners were used with two different reflector sizes and placed on two different background structures. One TerraSAR-X (TSX) image was acquired over this measurement setup in the highest-resolution staring spotlight mode, in which the subsequent analyses of radar backscatter were carried out. Additionally, the height adjustability of the IOSB corners was used in a persistent scatterer measurement campaign to create controlled height displacements.