The EXTENSE project, carried out from 1 October 2018 to 30 September 2023, aimed to develop a prototype multisensor measurement system capable of detecting and locating objects in marine sediments, such as submarine cables, underwater munitions and deep‑sea construction elements. A central element of the effort was the creation of an electrical impedance tomography (EIT) sensor array, together with image‑reconstruction algorithms that translate impedance variations into high‑resolution images of buried objects. In parallel, the team integrated complementary sensing modalities—including magnetometers, ultrasound transducers and altimeters—to enrich the data set and improve detection reliability. The sensor fusion strategy was implemented in software, allowing the system to combine the distinct physical signatures captured by each modality into a single, more informative output. The hardware design emphasized robustness, with components engineered to be partially waterproof and pressure‑resistant for deployment in marine environments. A user‑friendly interface was also developed to streamline sensor configuration, facilitate commissioning, and provide expert diagnostics and error handling, thereby reducing operator workload and improving data quality.
The technical workflow followed a spiral development model, structured into four major work packages and ten sub‑packages. Work package 1 focused on concept design, requirement analysis and component selection. Work package 2 handled hardware integration, including the construction of the EIT sensor board and the assembly of the additional sensor modules. Work package 3 concentrated on simulation and algorithm development; here, the team built numerical models of the EIT, magnetometer and ultrasound systems, derived reconstruction algorithms for EIT, and implemented sensor‑fusion routines. Work package 4 encompassed validation and evaluation, with laboratory experiments to test sensor performance and field trials conducted in the North and Baltic Seas to assess real‑world operation. Throughout the project, iterative cycles of testing and refinement were carried out, and two cost‑neutral extensions were added to accommodate delays caused by the COVID‑19 pandemic and a shortage of skilled personnel. These extensions allowed the team to deepen its understanding of sensor behaviour, refine the modular architecture, and enhance the data‑driven structure of the platform.
The project was funded with €636,904, of which €457,124.98 was allocated to scientific staff (TVöD/TV‑L levels E12–E15 and BAT IIa–I) and €41,183.72 to student assistants. The Technical University of Lübeck, under the leadership of Prof. Dr. Horst Hellbrück, served as the principal investigator. The research benefited from the infrastructure of the CoSA competence centre, which provided servers, a web portal, version control, a local MQTT broker and a MATLAB licence server. Seven students were recruited for theses and projects through the university’s web presence, demonstrating the project’s educational impact.
Collaboration was key to the project’s success. The Sea & Sun Technology GmbH coordinated the effort, while J&C Bachmann GmbH and Fugro Germany Marine GmbH (associate partner) contributed industrial expertise and field testing facilities. The close integration of tasks across these partners enabled rapid prototyping, efficient data exchange, and the practical validation of the multisensor system in realistic marine settings. The resulting platform not only advances the state of the art in underwater object detection but also provides a foundation for future commercial deployment and academic training in marine sensing technologies.