High performance numerical architecture for Distributed Acoustic Sensing – ANTIPASTI

The deployment of DAS (Distributed Acoustic Sensing) system is booming both for civilian, military and intelligence applications. In particular, these systems enable underwater passive acoustic surveillance. Currently available DAS systems have spatial resolutions of a few meters and can interrogate long distances of fiber (>100 km). Their spatial resolution is limited by the width of the optical pulse generated by the interrogator and sent into the fiber to detect and locate the acoustic perturbation.
In the framework of a CIFRE-AID PhD thesis, Thales has developed an FMCW DAS system allowing to interrogate fibers over a distance of a few kilometers but with a high spatial resolution (~10 cm) and sampling frequency (~10 kHz), unmatched to date. These features are perfectly in tune with the new requirements expressed for civil and military applications, in particular those linked to the introduction of drones in underwater warfare.
As for all DAS systems, compactness, power consumption and the amount of data generated are major obstacles to the miniaturization and embeddability of a DAS system. In the present case, the solution implemented at Thales since 2019 relies on the digital correction of imperfections in the frequency modulation of the emitting laser. While this digital correction technique, which stems from TRT's work on lidar systems, provides a more spatially and temporally resolved measurement, it imposes more constraints on the computing and sampling capacities of the digital block.
To meet in the best way possible the strategic needs of the defense industry, the ANTIPASTI project puts forwards an innovative and comprehensive approach to the digital architectures that make up an FMCW DAS (algorithm, adjustable digital precision and energy efficiency) as well as on their integration with existing or original optical blocks.
The first objective of the project is to improve the processing block (1) with a new algorithm (to ensure that processing is efficient, in particular through parallelization) and correctly sized and used computing functions (2) by implementing software functions on the most energy-efficient computing cores, with efficient data transport and (3) by implementing a mixed precision code for greater efficiency while guaranteeing the numerical stability of the results.
This work will enable us to provide an initial high-performance optimized "digital block" compatible with Thales's existing FMCW DAS interrogators (TRT and UWS). This digital block optimization will also enable us to identify the best hardware and software configuration compatible with an embedded DAS.
The second objective of ANTIPASTI is the conception of a portable DAS adapted to the needs of the military. To the best of our knowledge, this type of system does not exist. On top of requiring a particular effort on data management and overall power consumption, a redesign of the optical core is necessary, using integrated photonics for certain functions. A new optical block will be integrated with a second, reduced SWaP digital block.
In order to validate the improvements made to the system and quantify the difference in performance between a portable DAS and a traditional static FMCW DAS, experiments already carried out at TRT involving the acoustic detection of a microdrone by DAS will be repeated with the two interrogators. Tests under realistic simulated conditions (water filled tank and controlled low-noise environment) are planned at TDMS. Once again, the performance of two interrogators will be compared. Particular attention will be paid to the minimum spatial resolution achievable by these two interrogators.
By combining the expertise of a worldwide-renowned laboratory on high performance calculus (LiP6) and that of experts at Thales R&T and Thales DMS, ANTIPASTI will provide an ambitious and coherent maturity rise to the DAS systems developed at Thales since 2019.