In order to evaluate the performance of laser-based applications in maritime environments, laser beam propagation studies over the Baltic Sea during the period of about half a year have been carried out. A slightly slanted path with the laser system located 18 m above the sea level and corner cube targets and separate receivers placed on islands at 2.5-, 5.5-, and 16.5-km distance were used. From the registered laser signals irradiance fluctuation parameters for different beam offsets relative to the beam's center, temporal, and amplitude signal distributions, we derived the probability and mean time of fade. Results and statistics from single and double propagation paths are compared.
This paper will describe single and double path laser link measurements over land and sea. The laser system consisted of a CO2 laser, a pointing and tracking head, a quadrant laser receiver, a 3-5 μm IR-camera, a TV camera and a laser range finder. For the naval scenario the laser system was placed in a building 18 m above water and corner cube targets and a single path receiver were placed on islands at 2.5, 5.5 and 16.5 km. For the land scenario the laser system was placed in a building about 13 meters above ground looking at targets and a single path receiver at 2 km range. Together with the laser registrations, separate instruments such as a scintillometer and a weather station were recording the
meteorological parameters. The analysis contains evaluation of temporal and amplitude signal distributions, probability and mean time of fade and tracking performance. Results from single ended and double ended paths will be compared. Different ways of using this database for turbulence simulation and laser system performance predictions also in other wavelength regions will be discussed as well as the impact on applications including laser imaging, free-space laser communications and directed infrared countermeasures.
Directed infrared countermeasures (DIRCM) play an increasingly important role in electronic warfare to counteract threats posed by infrared seekers. The usefulness and performance of such countermeasures depend, for example, on atmospheric conditions (attenuation and turbulence) and platform vibrations, causing pointing and tracking errors for the laser beam and reducing the power transferred to the seeker aperture.
These problems make it interesting to simulate the performance of a DIRCM system in order to understand how easy or difficult it is to counteract an approaching threat and evaluate limiting factors in various situations. This paper describes a DIRCM model that has been developed, including atmospheric effects such as attenuation and turbulence as well as closed loop tracking algorithms, where the retro reflex of the laser is used for the pointing control of the beam.
The DIRCM model is part of a large simulation framework (EWSim), which also incorporates several descriptions of different seekers (e.g. reticle, rosette, centroid, nutating cross) and models of robot dynamics. Effects of a jamming laser on a specific threat can be readily verified by simulations within this framework. The duel between missile and countermeasure is simulated in near real-time and visualized graphically in 3D. A typical simulation with a reticle seeker jammed by a modulated laser is included in the paper.
Directed infrared countermeasure (DIRCM) systems are being developed in several configurations ranging from open loop, closed loop (CLIRCM) and lately for preemptive use (PIRCM). Critical performance parameters, from an atmospheric propagation point of view, include attenuation as well as turbulence effects on target detection, tracking and the capability to deliver enough power to the target (power in bucket). In order to evaluate the performance of DIRCM and other laser applications in a naval environment we have performed laser beam propagation studies over the Baltic Sea during June to October 2003. The experimental data were used to derive atmospheric attenuation, irradiance fluctuation parameters for different beam offsets relative to the beam centre, temporal and amplitude signal distributions, probability and mean time of fade and tracking performance. Results from simultaneous single and double-ended paths were obtained. This paper will shortly summarize the results from this campaign, and discuss and exemplify how the results can be used for prediction of DIRCM system performance.
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.