When High Resolution Goes Wrong: Low-Frequency Distortion in Linear Radon-Based Dispersion Imaging

Dispersion imaging is a key step in Multichannel Analysis of Surface Waves (MASW) for estimating the shear-wave velocity structure of the subsurface. High-resolution linear Radon transform (HRLRT) was introduced to improve spectral resolution; however, it is known to suffer from model-incompatibility and near-field effects. In this study, we show that even in the absence of near-field effects, the inner and outer iterative structure of HRLRT systematically modifies the low-frequency portion of the dispersion image. While high-frequency spectral energy in the wavenumber domain is improved, the low-frequency energy is distorted, leading to a shift in the extracted dispersion curves when compared with beamforming and other wavefield-transformation methods. This behaviour can introduce bias in phase-velocity picking and subsequently in shear-wave velocity inversion, particularly for deep layers controlled by low-frequency data. Our results highlight a trade-off between resolution and physical fidelity when using HRLRT for MASW dispersion analysis.