Design of a flexible, re-usable hardware component for the 2D discrete wavelet transform

This paper deals with the implementation of the 2D discrete wavelet transform in the form of a reusable, flexible hardware component. This component is compliant with the JPEG2000 standard and targets a variety of embedded imaging applications. A novel design methodology based on the emerging high-level synthesis tools allowed us to achieve a high degree of flexibility in the specification and synthesis of this component. Customization of functional parameters is supported (choice of the lifting-based filter bank, number of decomposition levels) as well as communication constraints (pixel ordering and I/O scheduling) and performance constraints (computation speed and parallelism), facilitating reuse in various applications and integration environments. In this paper, we first provide a summary of the recent trends in embedded system design. Then the theoretical bases of the discrete wavelet transform and the classical approaches for implementing it in hardware are briefly presented. After presenting the principles of our design methodology, we detail the successive design stages, from the algorithm to the architectures, in the case of the 2D lifting-based discrete wavelet transform. We conclude with synthesis results demonstrating the effectiveness of our approach for designing highly flexible hardware components.Dans cet article, nous nous intéressons à l'implantation matérielle de la transformation en ondelettes discrète 2D sous forme d'un composant réutilisable flexible. Ce composant, compatible avec le standard JPEG2000, est destiné à être intégré dans une variété d'applications embarquées de compression d'images. Une méthodologie de conception originale reposant sur les nouveaux outils de synthèse de haut niveau nous a permis d'atteindre un degré élevé de flexibilité dans la spécification et la synthèse de ce composant. Celle-ci autorise en effet la personnalisation de paramètres fonctionnels (choix du banc de filtres lifting, nombre de niveaux de décomposition), de contraintes de communication (ordre de parcours des pixels de l'image, date de lecture/écriture des données) et de contraintes de performances (vitesse de traitement, parallélisme de calcul) qui facilitent ainsi sa réutilisation dans différentes applications et environnements d'intégration. Dans cet article, nous dressons tout d'abord un état de l'art des nouvelles approches en conception de systèmes intégrés. Nous rappelons brièvement les bases théoriques de la transformation en ondelettes discrète et nous présentons les approches classiques pour son implantation sous forme d'architectures VLSI. Après avoir présenté les principes de notre méthodologie de conception, nous déclinons ses étapes successives, de l'algorithme aux architectures, dans le cas de la transformation en ondelettes 2D utilisant le Lifting Scheme. Nous concluons par des résultats de synthèse démontrant l'efficacité de la démarche suivie en termes de flexibilité de la spécification obtenue

First installation of an optical OBS, cabled offshore Les Saintes, Lesser Antilles

The detection, analysis and modeling of seismic processes worldwide very often requires the use of ocean bottom seismometer (OBS). Indeed, the largest earthquakes and transient slow slip events (SSEs) mostly occur offshore or near oceanic coasts, along the major plate boundaries, and in particular on the interplate thrust fault of subduction zones. However, most OBS deployments are done with stand-alone stations, with data recovery delayed by months or years. On the other hand, electrically cabled OBS, which allow for real-time monitoring, like in Japan (DONET), USA(Neptune), or France (EMSO Ligure), remain exceptional due to their very high cost of manufacturing, installation, and maintenance. Here we present a new perspective for such cabled array of OBSs, using innovative, purely optical seismometers, plugged at the end of long fiber optic cables, aimed at reducing the cost of installation and maintenance for permanent observatories requesting real-time data. The optical seismometer has been developped in the last decade by ESEO, based on Fabry-Perot (FP) interferometer, tracking at high resolution (rms 30 pm) the displacement of the mobile mass of a 10 Hz, 3 component, purely mechanical geophone (no electronics nor feedback). A prototype has been successfully installed at the top of La Soufrière volcano of Guadeloupe, in 2019, at the termination of a 1.5 km long fiber. We replicated and marinized this sensor, and in June 2021 we installed it 5 km offshore the Les Saintes islands (Guadeloupe, Lesser Antilles), for better characterizing the intriguing swarm-type activity still persistent after the 2004, M6.3, Les Saintes destructive earthquake (Interreg Caraïbe PREST project). The cruise, FIBROSAINTES, was supported by the Flotte Oceanographique Française (FOF) with the N/O Antéa Research Vessel. A plow, designed by GEOAZUR, carried the reel with its cable, and was pulled on the sea floor by the vessel, burying the cable. The seismometer was installed by divers at the depth of 43 m. The landing cable in the harbour of Terre-de-Bas was connected to the interrogator, and the record are since telemetered in real-time to the Observatory of Guadeloupe (OVSG). The optical OBS has been qualified by comparison to the records of the M7.5 Haiti 2021 earthquake from a nearby land-based broad-band seismometer. A few local earthquake swarms have been recorded, allowing for a preliminary discussion of their mechanical origin. In 2024 the seismometer should be complemented by two other ocean bottom, innovative, high resolution instruments, a pressiometer and an hydrostatic tiltmeter, designed by ENS. This successfull installation opens promising perspectives for the seismic real-time monitoring in many other sites offshore, and more generally in any site, natural or industrial, presenting harsh environmental conditions, where commercial, electrical sensors are difficult and/or costly to install and to maintain, or simply cannot be operated. Cite this article as (2022). First installation of an optical OBS, cabled offshore Les Saintes, Lesser Antilles, Seismol. Res. Lett. XX, 2-24, doi: