Single-and double-path laser link measurements over water

Small target detection and tracking are important for laser systems in many applications such as Directed Infrared Countermeasures (DIRCM), fire control, target recognition and free-space laser communication. In order to evaluate performance of these applications in a marine environment we have performed laser propagation studies over the Baltic Sea during May to October 2003. The laser system consisted of a CO2 laser, a pointing and tracking head, a quadrant laser receiver, a TV and 3-5 μm IR camera and a laser range finder. The laser system was placed in a building 18m above water and corner cube targets and separate receivers were placed on islands at 2.5, 5.5 and 17 km range. Together with the laser registration, separate instruments such as a scintillometer and a weather station were recording the meteorological parameters. From the received signals irradiance fluctuation parameters for different beam offsets relative to the beam centre, temporal and amplitude signal distributions, probability and meant time of fade were derived. Results from single- and double-ended paths will be compared. The results will be discussed in relation to theoretical modelling and evaluated in view of some system aspects.