201-9 Toward Rigorous Intercomparison of InSAR Products: Resolution, Validation, and Uncertainty in Coastal Subsidence Estimates

Abstract:

Interferometric synthetic aperture radar (InSAR) has become a primary tool for mapping coastal subsidence and vertical land motion (VLM) at fine spatial resolution, informing flood-risk, infrastructure, and sea-level-rise assessments across vulnerable coastlines. As multiple InSAR-derived products now cover overlapping regions, the community increasingly relies on cross-product comparison to assess reliability. However, the methodology used to compare products can itself introduce substantial artifacts, and disagreement between products is often attributed to underlying data quality when it instead reflects choices made in the comparison framework. We examine three such choices using coastal subsidence products for the U.S. Gulf Coast as a case study. First, spatial aggregation prior to comparison can reduce pixel density by orders of magnitude, suppressing genuine fine-scale variability and manufacturing apparent disagreement at coarser scales. Second, GNSS validation networks selected for geophysical stability versus those spanning a product's full application domain answer different questions about accuracy and should not be treated as interchangeable. Third, disagreement thresholds derived from inter-product spread, rather than from independent uncertainty quantification, can be internally inconsistent, in some cases flagging results that are not otherwise in dispute. We further show that differences in observation window between compared products can alone account for a substantial share of reported disagreement, independent of any error in either dataset. Together, these findings argue for a set of shared benchmarking practices: common reference validation networks with transparent processing documentation, standardized reporting of spatial resolution and observation window alongside published products, and uncertainty thresholds grounded in first-principles error propagation rather than inter-product comparison. We propose a coordinated community forum, following models such as ISSI International Teams, to establish these standards and improve the reproducibility of InSAR-derived geodetic products more broadly.

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