Optimized GNSS Cal/Val Site Selection for Expanding InSAR Viability in Areas With Low Phase Coherence: A Case Study for Southern Louisiana

Interferometric synthetic aperture radar (InSAR) techniques can be used to derive spatially dense “relative” measurements of vertical land motion (VLM), whereas global navigation satellite system (GNSS) provides point-based “absolute” measurements of VLM. The combination of GNSS and InSAR observations can yield spatially dense VLM measurements in an absolute reference frame. In addition, GNSS observations can be used to correct atmospheric noise in InSAR deformation measurements and serve as a complementary measure to isolate deep and shallow subsidence components. Given the increasing spatial and temporal coverage available from InSAR satellites, there is a need to establish calibration/validation networks that enable the use of InSAR for measuring VLM in coherence-challenged areas such as many low-lying coastal lands. In this study, we provide a method for the selection of sites for new GNSS installations such that the resulting GNSS network can better serve as tie points and validation for InSAR in areas where low coherence prevents high-fidelity phase unwrapping. Our method is applied in a case study for expanding the existing GNSS network in southern Louisiana, using abandoned oil well sites as potential sites. Considering practical limitations, distribution among various land classes, and following National Geodetic Survey guidelines, our proposed GNSS network consists of 61 (45 existing + 16 new) stations spread over a 50 000 km ² area of southern Louisiana.