ECHO project: Multi-parameter calibration of the GeoLab DAS fibre, Madeira, Portugal

Distributed Acoustic Sensing (DAS) enables broadband strain measurements with exceptional spatial and temporal resolution, effectively transforming fibre-optic cables into dense sensor arrays. Its ability to operate continuously and cost-effectively in challenging environments makes DAS a powerful tool for geophysical, seismological, and oceanographic research. However, the lack of adequate transfer functions linking DAS strain measurements to true ground motion remains a key limitation for its reliable use in quantitative seismic analysis.

Project ECHO (Earthquakes, Currents, Hydroacoustics, and Oceanography) addresses this limitation by establishing local, empirically derived transfer functions for the GeoLab fibre. By deploying a suite of collocated reference instruments along the cable track, the project will characterize the contributions of ground motion, temperature, pressure, and oceanographic processes to the measured DAS strain, and also quantify cross-sensitivities between these parameters.

To constrain strain and ground motion, two ocean-bottom seismometers equipped with additional pressure and temperature sensors will be deployed at water depths exceeding 2000 m, complemented by a land-based seismic station. Oceanographic variability will be monitored using acoustic Doppler current profilers (ADCPs) and conductivity, temperature, depth (CTD) sensors. Hydrophones will serve as an independent reference for calibrating the DAS response to underwater acoustic signals, including marine mammal vocalizations and anthropogenic sound sources, with complementary confirmation of low frequency signals from the ocean-bottom seismometers.

Expected outcomes include segment-specific DAS transfer functions, a DAS-derived seismic catalogue, detection and classification of marine mammals from their vocalizations, the development of DAS-based proxies for sea-state variability, and an assessment of the feasibility of shear-wave splitting analysis given the existing cable geometry. Together, these results will advance understanding of regional seismicity, ocean dynamics from the coastal zone to the deep basin, and underwater acoustics, while substantially enhancing the scientific utility and applicability of DAS in Earth and marine sciences.

The richness of the multi-parameter datasets acquired within ECHO create significant opportunities for interdisciplinary collaboration, providing a unique framework for joint studies across seismology, physical oceanography, marine ecology, and fibre-optic sensing. This integrated approach is intended to foster collaboration within the broader scientific community and to stimulate the development of novel methodologies and applications beyond the immediate scope of the project.

All datasets generated by ECHO will be released under F.A.I.R. principles at the conclusion of the project.

This work is supported by the ECHO project (DOI: 10.54499/2024.13655.PEX), ARDITI - Agência Regional para o Desenvolvimento da lnvestigação, Tecnologia e lnovação, the SUBMERSE EU project (GA 101095055), and FCT, I.P./MCTES through national funds (PIDDAC): LA/P/0068/2020 (DOI:10.54499/LA/P/0068/2020), UID/50019/2025 (DOI: 10.54499/UID/50019/2025), UID/PRR2/50019/2025 (DOI: 10.54499/UID/PRR/50019/2025).