Space-based InSAR with sub-daily temporal baselines

Evan L Kramer, Brent M Minchew

Interferometric synthetic aperture radar (InSAR) underpins the Surface Deformation and Change observable prioritized by the 2018 decadal survey, yet the temporal sampling of current assets aliases many transient geophysical processes. For single-satellite repeat-pass InSAR, satellite orbits accommodate temporal baselines at integer nodal day intervals down to a single nodal day. Processes that evolve over minutes to a couple days are undersampled by these systems. This work presents a constellation architecture, termed Tunable WIndow for Surface Transients (TWIST), that acquires cross-satellite interferograms at programmable sub-daily temporal baselines by distributing SAR satellites across multiple orbit planes. Orbit phasing as a function of desired temporal baseline is formalized into plane orientation and inter-orbit satellite position conditions that align the satellites’ ground tracks in the Earth-fixed frame under J2- perturbed dynamics. Routine science and on-demand operating strategies are evaluated through modeled spatial coverage, average response time, and three-dimensional displacement retrieval feasibility. A four-satellite TWIST InSAR constellation observes 99.8% of global land at sub-daily temporal baselines, achieves an on-demand average response time of 6.7 hr, and offers threedimensional displacement retrieval for 91.1% of global land. The presented results demonstrate the game-changing observation capabilities of the TWIST InSAR architecture for nine previously identified targeted observables while showing no major technical hurdles in acquisition of the orbit phasing conditions.