For underwater applications, laser based technologies offer a complementary solution to existing sensors (sonar) for the detection and identification of underwater targets, particularly in shallow waters or in complex marine terrain such as archipelagos with numerous small islands, narrow sounds and inaccessible locations.

This is the main result of a study commissioned by the European Defence Agency (EDA) and conducted by a consortium consisting of FOI, the Swedish Defence research Agency, and ISL, the French-German Research Institute of Saint-Louis.

The study details the use of laser systems - both LIDAR-based (Light Detection and Ranging, a remote sensing method that uses light in the form of a pulsed laser to measure ranges) and LADAR-based (LAser Detection And Ranging) - and indicates that their successful incorporation into existing detection and identification technologies for underwater targets in difficult operating conditions, such as those found in the Baltic Sea, can have a significant and positive impact on performance, particularly for rapid detection and identification.

Laser systems can deliver operational improvements as compared to sonar systems: airborne laser scanning, for instance, can be deployed extremely quickly in order to detect, locate and track underwater or floating objects. It is also possible for airborne laser scanning to identify the types of targets, provided that the target is large enough. Once a target is detected it is then possible to quickly deploy a surface or underwater vessel equipped with a Laser Gated Viewing (LGV) or Underwater Laser Scanning (ULS) system to positively identify confirm the target information.

The study concluded that laser based technologies are a viable and complementary solution for acoustic sensor systems, even in turbid waters or in waters with high organic content, such as shallow regions or archipelagos found in the Baltic Sea.

Methodology

In order to analyse the performance of these technologies, three scenarios were defined: (1) Maritime mine identification, (2) Autonomous underwater vehicles (AUVs) and submarines detection and (3) Rapid environmental assessment (REA).

The study used modelling techniques along with systems knowledge to assess the performance of laser baser underwater systems. In order to assess the performance of the systems in the defined scenarios and tasks, the conditions and systems were simulated.

Background

The task to detect and identify underwater targets has traditionally been undertaken by sonar based systems, particularly in open water conditions and in waters with significant depths. However, there are situations where sonar-based systems could be assisted by complementary technology in order to achieve improved performance. Examples of such operating conditions are relatively shallow waters where sonars ships cannot operate and complex marine terrain such as coastlines with archipelagos numerous small islands, narrow sounds and inaccessible locations.

The Baltic Sea, due to its high level of turbidity in coastal regions is one such area that is particularly challenging for the detection of underwater targets using laser based sensors. The occurrence of organic matter such as algae and the effect of sediment transport in the water column coupled with the seasonal optical attenuation contribute to difficulties in detecting underwater targets.

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