Distributed Acoustic Sensing (DAS) has emerged as a transformative technology for near-surface site characterization. When a vertical source is activated along the fiber, DAS measures only the in-line (radial) component of Rayleigh-wave motion. Dispersion data extracted from radial-component waveforms may differ from those obtained from vertical-component measurements, particularly under complex stratigraphic conditions. Hence, a component-consistent forward problem is desired when inverting radial-component DAS dispersion data to retrieve accurate shear wave velocity (Vs) profiles. This study presents a radial-component predominant-mode (RCPM) inversion framework designed for DAS-based surface-wave analysis that explicitly accounts for source-receiver directivity and modal sensitivity of the Rayleigh-wave radial component. The proposed approach matches measured dominant radial dispersion trends with the theoretical mode exhibiting the maximum modal participation. As a result, the RCPM framework eliminates the need for explicit modal indexing, provides a component-consistent interpretation of radial-component dispersion data, and substantially reduces reliance on subjective analyst-driven modal interpretations. The RCPM approach is systematically evaluated using three synthetic ground models and two field DAS datasets. The synthetic results demonstrate that modal energy distribution differs significantly between vertical and radial components in the presence of strong velocity contrasts and velocity reversals, and that conventional inversion approaches may misinterpret modal behavior, resulting in less accurate Vs profiles. In contrast, the RCPM method consistently captures the correct modal response and yields reliable Vs profiles. Application to two field DAS datasets further demonstrates good agreement between the inverted Vs profiles and independent invasive borehole measurements.

翻译：分布式声学传感（DAS）已成为近地表场地特征化的一项变革性技术。当沿光纤激发垂直震源时，DAS仅测量瑞利波运动的面内（径向）分量。从径向分量波形中提取的频散数据可能与垂直分量测量获得的结果有所不同，尤其是在复杂地层条件下。因此，在对径向分量DAS频散数据进行反演以获取准确剪切波速（Vs）剖面时，需要建立分量一致的工程正演问题。本研究提出了一种适用于DAS面波分析的径向分量主模式（RCPM）反演框架，该框架明确考虑了瑞利波径向分量的震源-接收器方向性及模态灵敏度。所提方法将实测径向主导频散趋势与具有最大模态参与度的理论模式相匹配。因此，RCPM框架消除了显式模态索引的需求，实现了径向分量频散数据的分量一致性解释，并大幅降低了主观分析师主导的模态解释依赖性。通过三个合成地层模型和两个现场DAS数据集对RCPM方法进行了系统评估。合成结果表明，在存在强速度对比和速度反转的情况下，垂直分量与径向分量之间的模态能量分布存在显著差异，传统反演方法可能误判模态行为，导致Vs剖面精度不足。相比之下，RCPM方法能够始终捕捉正确的模态响应并生成可靠的Vs剖面。应用于两个现场DAS数据集进一步表明，反演得到的Vs剖面与独立侵入式钻孔测量结果具有良好的一致性。