When Rayleigh Fading Meets Rayleigh Waves: Artifacts and Mitigation in DAS Ambient-Noise Imaging

DATASET README ================================================================================ Project: Rayleigh-Fading Artifacts and Mitigation in DAS Ambient-Noise Imaging Data Type: DAS, Nodal Seismic, Virtual Shot Gather, and Gauge-Length Comparison Data Study Areas: Hangzhou and Lianyungang, China ================================================================================ 1. PROJECT OVERVIEW -------------------------------------------------------------------------------- Distributed Acoustic Sensing (DAS) enables densely sampled passive surface-wave imaging, but Rayleigh fading can destabilize optical phase recovery and introduce structured errors that survive interferometric correlation and stacking. This study examines how local fading-induced phase errors propagate through the DAS measurement chain and appear as broadband strain-rate transients, gauge-length- related anti-phase channel pairs, near-zero-lag energy in virtual shot gathers (VSGs), and oblique pseudo-dispersion bands. Based on this mechanism, the study develops spatially weighted dispersion imaging (SWDI) to reduce artifact-dominated offset contributions before phase-shift dispersion projection. The datasets provided here support comparisons among fading-contaminated DAS, normal DAS, and nodal observations; applications to urban dark fiber and purpose-buried fiber; and analysis of gauge-length-related zero-lag anticorrelation. The dataset contains three MATLAB MAT-files: 1. fading_normal_nodal_records_and_VSGs.mat 2. dark_and_buriedfiber_records_VSGs.mat 3. DAS_GL4m_GL8m_GL10m_dx4m_records.mat 2. FILE STRUCTURE AND DATA DESCRIPTION -------------------------------------------------------------------------------- ├── fading_normal_nodal_records_and_VSGs.mat │ │ Purpose: │ This file supports the comparison used to demonstrate how fading-related │ contamination affects DAS ambient-noise interferometry. It contains │ one-hour records from fading-contaminated DAS, normal DAS, and nodal │ observations, together with the corresponding interferometrically │ retrieved VSGs. │ │ Variables: │ │ uxt_fading │ One-hour DAS record containing pronounced fading-related noise. │ │ uxt_das │ One-hour normal DAS record used. │ │ uxt_node │ One-hour nodal seismic record used as an independent wavefield │ comparison. │ │ dt_fading, dt_das, dt_node │ Temporal sampling interval of uxt_fading, uxt_das and uxt_node. │ │ dx_fading, dx_das, dx_node │ Output-channel spacing of uxt_fading, uxt_das, uxt_node. │ │ vsg_fading, vsg_das, vsg_node │ VSG retrieved from the one-hour fading-contaminated DAS, normal DAS and nodal record. │ │ t_fading, t_das, t_node │ Correlation lag-time axis of vsg_fading, vsg_das and vsg_node in seconds. │ │ dx_vsg │ Common offset-bin spacing of the three VSGs, in meters. │ │ Scientific use: │ The file can be used to compare waveform characteristics, channel-wise │ spectra, correlation structures, stacked VSGs, frequency-wavenumber │ spectra, and dispersion images among fading-contaminated DAS, normal DAS, │ and nodal observations. │ ├── dark_and_buriedfiber_records_VSGs.mat │ │ Purpose: │ This file contains the DAS records and corresponding VSGs from two │ contrasting field deployments: an urban telecommunication dark fiber │ and a dedicated trench-buried fiber. The datasets are used to evaluate │ fading-artifact mitigation under different cable-installation and │ ambient-noise conditions. │ │ Variables: │ │ uxt_dark │ DAS record acquired along the urban dark-fiber deployment. │ │ uxt_cable │ DAS record acquired along the dedicated trench-buried cable. │ │ dt_dark │ Temporal sampling interval of uxt_dark, in seconds. │ │ dt_cable │ Temporal sampling interval of uxt_cable, in seconds. │ │ dx_dark │ Output-channel spacing of uxt_dark and vsg_dark, in meters. │ │ dx_cable │ Output-channel spacing of uxt_cable, in meters. │ │ vsg_dark │ VSG retrieved from the urban dark-fiber record. │ │ vsg_cable │ VSG retrieved from the trench-buried-fiber record. │ │ t_dark │ Correlation lag-time axis of vsg_dark, in seconds. │ │ t_cable │ Correlation lag-time axis of vsg_cable, in seconds. │ │ dx_cable1 │ Offset-bin spacing of vsg_cable, in meters. │ │ Scientific use: │ These records and VSGs support conventional and spatially weighted │ dispersion imaging for the two field deployments. They can be used to │ evaluate the suppression of near-zero-lag contamination and the │ preservation of coherent surface-wave dispersion ridges. │ │ └── DAS_GL4m_GL8m_GL10m_dx4m_records.mat │ │ Purpose: │ This file contains three 10-s DAS strain-rate records acquired or │ generated using nominal gauge lengths of 4, 8, and 10 m. All three │ datasets have a nominal output-channel spacing of 4 m. The records │ are used to examine gauge-length-related zero-lag anticorrelation │ and the broader phase-demodulation noise field. │ │ Recommended variable names: │ │ GL4 │ Ten-second DAS record with a 4-m gauge length. │ │ GL8 │ Ten-second DAS record with an 8-m gauge length. │ │ GL10 │ Ten-second DAS record with a 10-m gauge length. │ │ dt │ Common temporal sampling interval, in seconds. │ │ Scientific use: │ The datasets can be used to calculate zero-lag channel-correlation │ matrices and mean correlation coefficients as functions of │ channel-index lag. At a 4-m output spacing, gauge lengths of 4 and │ 8 m nominally correspond to channel-index lags of 1 and 2, │ respectively. The 10-m gauge length corresponds to a noninteger │ ratio of 2.5 and may appear at the nearest discretely sampled lag.