The MODAS project (Monitoring the Ocean with DAS) is a 3-year national project, starting in March 2023, and is a partnership between the lead partner Instituto Dom Luiz (IDL, www.idl.ciencias.ulisboa.pt), the Portuguese Institute for Sea and Atmosphere (IPMA, www.ipma.pt), the INESC-TEC research association (www.inesctec.pt), and the Telecommunications Institute (IT, www.it.pt ).
The main objective is to use Distributed Acoustic Sensing (aka DAS) on a submarine cable in the Azores to monitor during one year of the natural events and risks (earthquakes and tsunamis) and environmental risks (sea state, surface currents, soundscape, and whales).
DAS is an emerging tool that uses optical fiber as a distributed sensor, measuring local variations in the optical signal coupled to local mechanical changes of the fiber, with very high spatial and temporal resolution.
The DAS is a suitable tool for monitoring submarine fibers at distances of up to 100 km from the coast, both in short time scales, to provide real-time data as needed to emergency services, and also in the long term, of various essential ocean variables that are relevant.
Parameters that will contribute include solid earth, ocean, solid-ocean interactions, anthropogenic and natural noise sources, and whale vocalizations. They are all relevant to mitigating natural hazards and assessing the impacts of climate change on the ocean.
Within the MODAS project, we have been using an HDAS (High-Fidelity Distributed Acoustic Sensor) system, supplied by the University of Alcalá, to acquire data to monitor a submarine telecommunications cable linking the mid-Atlantic Azorean islands of Faial and Flores. The DAS system uses optical reflectometry in the time domain to measure the variation of the optical phase along the fibre on the seabed. The system can monitor up to 50 kilometers of cable, with a spatial resolution of 10 meters and a sampling rate of 50 Hz. The high sensitivity combined with a broadband response makes it possible to pick up high-frequency whale vocalizations, tsunami waves, and long-period tides
Instituto de Telecomunicações, in collaboration with its partners, has focused its activities on several important challenges, including the development of processing routines using advanced data analysis techniques, including f-k analysis, apparent phase velocity calculations, and power spectral density.
The aim is to establish robust correlations with data from nearby land-based seismic stations and from two ocean-bottom seismometers (OBS) installed in July 2024. The OBS also includes low-frequency hydrophones, allowing DAS signals to be compared with pressure signals generated by large infragravity waves, which serve as proxies for tsunami waves. The long-term goal is advancing towards efficient computing of relevant data sets and real-time earthquake monitoring, through products to be used by IPMA in the operational regime.
On this project: