SAR Imaging Geodesy with Electronic Corner Reflectors (ECR) and Sentinel-1 – First Experiences

Abstract

<p>SAR imaging geodesy is a new technique in the field of geodesy and remote sensing that enables the 3D localization of specifically designed radar targets. The absolute 3D position of a radar target in the ITRF can be estimated by means of least squares adjustment, when combining at least two sets of radar coordinates extracted from SAR images and the corresponding orbital arcs given by precise orbit determination. The installation of permanent radar targets allows for long-term position monitoring, making the technique a particularly interesting candidate for displacement and height change observations. While the principle of geodetic positioning with SAR is well-established, the selection of the radar target suitable for an application is subject to discussion. Parameters to be considered are the resolution of the radar images which can be provided by satellites like Sentinel-1 or TerraSAR-X, the size of the radar target with respect to the image resolution, the required localization accuracy of the selected application, and possible environmental and/or technical limitations at the installation site. Two main categories of artificial radar targets can be identified: passive reflectors and active transponders. Examples of passive reflectors that have been tested at geodetic observatories are corner reflectors, octahedron reflectors and tophats, while an example of active transponders is the experimental Electronic Corner Reflector (ECR).</p><p>The poster illustrates the first results acquired from the testing of ECRs operating in C-band, and their 3D localization using the IW medium resolution products of Sentinel-1A and 1B. The operation principle, the installation and mounting options, and the use of the ECRs as a small and portable alternative to passive reflectors are additionally discussed.</p>

Exploiting artificial reflectors for SAR interferometry applications

“…Concerning the active reflectors, one is the Electronic Corner Reflector at C-band (ECR-C) produced by MetaSensing [2], which is compatible with operation frequencies of Sentinel-1 (S1) and RADARSAT-2. The other two were designed in the early '90s for supporting the calibration of SAR sensors operating at C-band (ARC-C) and X-band (ARC-X) and used for the sensors onboard the NASA/JPL-DC8 aircraft and the SIR-C/X-SAR mission [3,4].…”

“…According to this, the signal coming from ERC-C is visible by Dataset-1, Dataset-2, and Dataset-3. The nominal RCS is 𝑅𝐶𝑆 𝑛 = 40 ÷ 42 𝑑𝐵𝑚 2 , which means that the device is equivalent to a passive CR of internal edge 𝑎 = 1.8 𝑚, which is a considerably larger than the ERC-C's size of 56𝑥36𝑥23 𝑐𝑚 3 . Both size and flexible visibility make the ECR-C clearly more advantageous with respect to passive reflectors.…”