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 GlobalNavigation Satellite System (GNSS) provides point-based“absolute” measurements of VLM. The combination of GNSS andInSAR observations can yield spatially dense VLM measurementsin an absolute reference frame. Additionally, GNSS observationscan be used to correct atmospheric noise in InSAR deformationmeasurements, and serve as a complementary measure to isolatedeep and shallow subsidence components. Given the increasingspatial and temporal coverage available from InSAR satellites,there is a need to establish calibration/validation (cal/val)networks that enable use of InSAR for measuring VLM incoherence-challenged areas such as many low-lying coastal lands.In this study, we provide a method for selection of sites for newGNSS installations such that the resulting GNSS network canbetter serve as tie points and validation for InSAR in areas wherelow coherence prevents high-fidelity phase unwrapping. Ourmethod is applied in a case study for expanding the existing GNSSnetwork in southern Louisiana, using abandoned oil well sites aspotential sites. Considering practical limitations, distributionamong various land classes, and following National GeodeticSurvey guidelines, our proposed GNSS network consists of 61 (45existing + 16 new) stations spread over a 50000 km2 area ofsouthern Louisiana.