BIOMASS SAR tomography: An insight from closure phase

Under short repeat-pass acquisitions of the BIOMASS satellite, TomoSAR stacks are commonly assumed to be temporally stationary in terms of vertical reflectivity profile. However, temporal decorrelation and short-term variations in canopy scattering mechanisms can introduce systematic inconsistencies across interferometric measurements, potentially biasing tomographic reconstruction. This letter investigates the impact of temporal decorrelation on BIOMASS-like TomoSAR observations through interferometric closure-phase analysis. A two-layer forest scattering model is adopted to physically relate closure-phase behavior to forest structure, system parameters, and variations in vertical reflectivity profile characteristics. Based upon this framework, a closure-phase stability index is introduced to quantify deviations from reflectivity consistency within regularly sampled TomoSAR stacks. The proposed index complements conventional interferometric coherence by targeting inconsistencies induced by temporal variations in the reflectivity profile, while coherence remains sensitive to both structural and temporal decorrelation. This letter further discusses how the insight from closure-phase analysis can be incorporated into tomographic data correction. The approach is evaluated using two sets of real data, demonstrating its potential as a physically grounded diagnostic tool for assessing temporal reliability in forest tomography.