Distributed Acoustic Sensing at the Engineering Scale: Experimental Insights from the PITOP Test Site

The PITOP geophysical test site, operated by the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS) in north-eastern Italy, provides a unique experimental environment for testing seismic acquisition technologies under realistic field conditions. Covering ~22,000 m², PITOP was established to support the development and validation of geophysical methods and instrumentation in both surface and borehole installations. Here, we evaluate PITOP’s potential for Distributed Acoustic Sensing (DAS) experiments, focusing on small-scale seismic measurements relevant to urban settings and engineering applications. 

Five boreholes with distinct purposes and instrumentation are available at the PITOP site, including a water well (PITOP1), two 400-m-deep wells associated with geosteering research (PITOP2 and PITOP3), a 150-m-deep borehole permanently equipped with optical fibre for DAS measurements (PITOP4), and a recently drilled well dedicated to geoelectrical surveys (PITOP5). The site also hosts a surface-deployed fibre-optic cable, containing both linear and helicoidal fibers, and about 20 3C seismic nodes. Finally, several seismic sources are available, which are a borehole Sparker Pulse, suitable for crosshole VSP configurations, and two surface vibratory sources, the IVI MiniVib T-2500, which can generate sweeps in the 10–550 Hz frequency range, and the ElViS VII vibrator, designed for frequencies between 20 and 220 Hz.

We conducted three dedicated experiments:  (i) cross-hole measurements with sources in PITOP3 at depths of 10, 50, 75, and 100 m, and DAS recording in PITOP4; (ii) a vertical seismic profiling (VSP) survey using the MiniVib source close to the well head with DAS recording in PITOP4; and  (iii) recordings of the seismic wavefield generated by P- and S-wave vibratory sources using surface DAS arrays in linear and helicoidal configurations, together with co-located 3D geophones for comparison.

DAS data were acquired with multiple gauge lengths and acquisition settings. The resulting datasets enable a systematic evaluation of acquisition parameters selection and highlight processing strategies required for different DAS configurations. They provide a valuable basis for assessing optimal DAS acquisition strategies for small-scale seismic applications and for defining processing workflows adapted to diverse source and receiver geometries.

The present study is being carried out within the framework of the USES2 project, which receives funding from the EUROPEAN RESEARCH EXECUTIVE AGENCY (REA) under the Marie Skłodowska-Curie grant agreement No 101072599.

This research has been supported by the Interdepartmental Research Center for Cultural Heritage CIBA (University of Padova) with the World Class Research Infrastructure (WCRI) SYCURI—SYnergic strategies for CUltural heritage at RIsk, funded by the University of Padova.