LINE EW-UAS - an experimental unmanned system for coastal surveillance using ESM technology

Drones and unmanned systems are attracting increasing interest from both military and civilian authorities alike, particularly in connection with surveillance and security technologies. An example of a use case for such an application is surveillance of maritime traffic along the coast. All vessels above a certain size are required to broadcast an Automatic Identification System (AIS) signal to identify themselves and their current position. Not everyone do this, which could be a sign of a vessel trying to pass by unnoticed. A system that verifies the existence of a ship where there is an AIS track, or localises a ship where there is no AIS track, would therefore be of great operational interest. Electronic Support Measures (ESM) is a technology for passive collection and interpretation of electromagnetic signals, such as e.g. radar pulses. Two or more coordinated ESM sensors can use this information to geolocate the emitting radar. A ship that is deliberately faking its AIS signal is unlikely to run the risk of also turning off its navigation radar, making ESM a potential technology for the described coastal surveillance system. The passive nature of an ESM sensor also makes it well suited for deployment on Unmanned Aerial Vehicles (UAV), where battery time and payload size are important factors. This report describes a complete system for geolocation of rotating maritime navigation radars using two UAVs equipped with ESM-sensor payloads. The payloads collect radar pulses from ships in the surrounding area and send pulse-metadata to a ground node where the information is coordinated and the results are presented in tools familiar to operational decision makers. The project has been carried out jointly between 8 different research groups from 5 different departments at the Norwegian Defence Research Establishment (FFI) and was created to highlight some of the opportunities and challenges of operating unmanned systems in an Electronic Warfare (EW) context. This has addressed a wide range of topics such as UAV operations and payload modification, 3D-printing, ESM technology, communication infrastructure, sensor networks as well as post-processing and presentation of data. This work demonstrates that geolocation of rotating navigation radars is possible using two small, affordable ESM sensors. Examples are given of radars being tracked over time, highlighting the technologies’ potential in applications for coastal surveillance. A complete, functional data chain is also shown: from antenna to high-level presentation tool in the operation room.