Orienting and locating ocean-bottom seismometers from ship noise analysis

Abstract

Summary Breakthroughs in understanding the structure and dynamics of our planet will strongly depend upon instrumenting deep oceans. Progress has been made these last decades in ocean-bottom seismic observations, but ocean-bottom seismometer (OBS) temporary deployments are still challenging and face set-up limitations. Launched from oceanographic vessels, OBSs fall freely and may slightly drift laterally, dragged by currents. Therefore, their actual orientation and location on the landing sites are hard to assess precisely. Numerous techniques have been developed to retrieve this key information, but most of them are costly, time-consuming or inaccurate. In this work, we show how ship noise can be used as an acoustic source of opportunity to retrieve both the orientation and the location of OBSs on the ocean floor. To retrieve the OBS orientation, we developed a first method based on a combination of seismic and pressure data through the use of the acoustic intensity. This latter can be used to quantify the OBS orientation from the ship noise direction of arrival (DOA), which can then be compared with known ship trajectories obtained from the automatic identification system (AIS). To accurately relocate OBSs, we also developed a second method based on the hydrophone data which computes distances of acoustical sources by measuring time differences of arrival (TDOA) between direct and reverberated phases. The OBS location is then retrieved by fitting measured ship distances with known ship trajectories. In this study, a full network of OBSs deployed in the SW Indian Ocean was reoriented and a test station was relocated. We demonstrate that our new methods may quantify the OBS orientation with an accuracy of about one degree, and its location with an accuracy of a few tens of metres, depending on the number of ships used in the analysis.

Noise Levels and Signals Observed on Submarine Fibers in the Canary Islands Using DAS

“…Ocean Bottom Seismometers (OBS) and hydrophone arrays commonly record seismic and hydroacoustic signals from ships. These signals have been used, for instance, as a source of opportunity for locating and orienting ocean bottom instrumentation (e.g., Trabattoni et al, 2020). Due to its geostrategic location, the Canary archipelago presents intensive ship traffic.…”

Impact of Anthropogenic Activities on Underwater Noise Pollution in Venice

“…4b of Trabattoni et al. ( 2020 ). Audio data show qualitatively similar spectral peaks at relatively low frequencies (below 500 Hz), with one isolated peak at 800 Hz.…”

Ship detection and tracking from single ocean-bottom seismic and hydroacoustic stations

“…To achieve this, we propose a Bayesian framework for detection and tracking adapted to underwater passive monitoring at low frequency with AVSs. This work is the continuation of a previous study (Trabattoni et al, 2019) in which ship noise was used to derive the accurate orientations and localizations of OBSs from AIS-derived ship positions. Here, we approach the inverse problem: how to retrieve blindly the trajectory of a ship from hydro-seismological records of a single station lying on the ocean floor.…”