tidal-insar-sim: an open-source toolkit for tide-aware ranking of NISAR L-band acquisitions over Antarctic grounding lines

Abstract. Double-difference InSAR (DDInSAR) is the standard remote-sensing technique for mapping ice-shelf grounding lines (GLs). The signal magnitude depends on the instantaneous ocean tide at all three epochs of the rigid acquisition triplet, the SAR sensor wavelength and incidence angle, and the elastic-plate response of the floating shelf. NASA's NISAR mission, in routine Antarctic operations since the first year of service, provides the first sustained open-access L-band InSAR coverage of the ice sheet but its 12-day exact-repeat orbit closely aliases the K1 diurnal ocean tide, the dominant tidal constituent at most Antarctic GLs. We present tidal-insar-sim, an open-source Python toolkit that ingests NISAR's operational Reference Observation Plan via the live ArcGIS feature service, auto-discovers per-track acquisition UT, pass direction, frame geometry, polarisation and bandwidth from the reference observation plan (ROP) fields, evaluates the CATS2008 ocean-tide model at the exact UT of every scheduled acquisition, enumerates rigid 12-day triplets per InSAR-coherent track stream, and ranks them by predicted DDInSAR fringe count. Applied to the three Amundsen Sea Embayment grounding lines contributing most to current global mean sea-level rise (Thwaites, Pine Island, Smith) over the first year of operations (Sep 2025–Sep 2026), we find that the ROP schedules every operationally feasible track at the coast, confirming zero coastal culling, yielding 793 rigid 12-day triplets across the three GLs. Of these, only 11 % cross the 3-fringe usability threshold and only 0.6 % reach the 5-fringe excellent-quality threshold. Tide-aware ranking elevates the 87 operationally usable triplets out of the long unusable tail and, in the event of an anomaly-driven duty-cycle reduction, retains 100 % of usable yield even under 50 % culling because the operational gold is concentrated in the top quintile. The same machinery generalises to repeat-track altimetry missions targeting NASA's Surface Topography and Vegetation Designated Observable. The code (MIT license) is openly archived on Zenodo and adaptable to any SAR or altimetry constellation with a published acquisition plan.