Performance analysis of conventional and next-generation artificial geodetic radar reflectors

Abstract

The introduction of artificial reflectors in the areas to be imaged by a radar sensor facilitates interferometric analysis over regions of weak coherence between acquisitions. Traditionally, corner reflectors have been utilized; whose strong and stable scattering characteristics make them suitable for these purposes. Such reflectors also provide flexibility in exerting control over the network of points to be analyzed. However, the use of these reflectors is beset with the following challenges: settlement under self-weight, inefficient drainage retaining excess rain/snow, one setup per track etc. Based on the experiment carried out with several reflector devices at Wassenaar, The Netherlands, here we show that specific next-generation artificial reflectors can address some of the challenges posed by conventional corner reflectors while allowing the integration of measurements from several deformation monitoring techniques. As part of the experiment, a deliberate 7±0.05 mm vertical movement is imparted to radar transponder MUTE-1 which is estimated from Sentinel-1 radar images within 0.01 to 0.69 mm deviation while the line of sight motion and radar cross section change realized as a result of imparting deliberate tilt to DBFm device is estimated within 0.47 mm and 1.7 dBm² respectively. The displacement results from SAR images for MUTE radar transponders are validated using a ground survey campaign. Displacement results in the horizontal direction (East-West projection) suggests that the location WASS01 housing devices MUTE-1 and DBFT tilts in the western directions (estimates of maximum tilt vary from 0.9 to 1.95 mm) while WASS02 location on which MUTE-2 is installed exhibits an eastward tilt (about 2 mm in magnitude). These tilt motions result from the susceptibility of concrete foundation design to swelling and shrinkage of soil. By analyzing meteorological data in conjunction with SAR results from installed devices, we find that the impact of heavy rain remains limited to the conventional reflector type, suggesting that the downward-pointing design of DBF CRs drains the water preventing its accumulation in the apex. Comparative stability analysis demonstrates that next-generation reflector devices (MUTE-2, DBFT and DBFX) can be utilized to determine motions in the vertical and horizontal direction and detect changes in orientation of the device over a vegetation area with low backscattering characteristics with sub-millimeter precision. We anticipate this study to be a small step towards a more sophisticated ground segment for SAR satellites consisting of reflectors that can adequately provide knowledge about deformation characteristics of the area under investigation.