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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.

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This study investigates the possibility of causing a vitreal hemorrhage with a standard ruby rangefinder at battlefield engagement distances when the laser is observed with the naked eye or through magnifying optics or filters. The experiments were undertaken on the eyes of anesthetized pigs. The pigs were anesthetized with Mebumal and given 0.5% thropicamid in the eyes. They were then exposed to the radiation from a standard military ruby rangefinder (pulsewidth 25 ns, pulse energy 180 mJ). The rangefinder was aligned with a He-Ne laser and a beamsplitter. Eight experiments were performed, each with several exposures. The range was varied from 0.5-850 m. Some of the experiments were made using the naked eye, some with a filter, some with binoculars (7 x 50) and some with a combination of filter and binoculars. The pulse energy was varied from 91-6500 muJ. Vitreal hemorrhages were caused at distances of 410 and 850 m when a pair of binoculars (7 x 50) was placed in front of the eyes. The intraocular energy varied between 1500 and 4400 microJ. Results indicate that there is a possibility of causing a vitreal hemorrhage in a soldier who is using standard field binoculars and looking in the direction of an ordinary military rangefinder at distances at least up to 850 m.

The main purpose of the work presented here is to study the potential for an active imaging system for target recognition at long distances. This work is motivated by the fact that there are a number of outdoor imaging needs where conventional passive electro optical (EO) and infrared (IR) imaging systems are limited due to lack of photons, disturbing background, obscurants or bad weather. With a pulsed illuminating source, several of these problems are overcome. Using a laser for target illumination, target recognition at 10's of km can be achieved. Powerful diode pumped lasers and camera tubes with high spatial and time resolution will make this technique an interesting complement to passive EO imaging. Beside military applications, civilian applications of gated viewing for search and rescue, vehicle enhanced vision and other applications are in progress. To study the performance limitations of gated viewing systems due to camera, optics and the atmosphere an experimental system was developed. Measurements up to 10 km were made. The measurements were taken at the wavelength 532 nm. To extrapolate the results to future system performance at an eye safe wavelength, 1.5 µm nm, a theoretical performance model was developed. This model takes into account the camera and atmospheric inßuence on resolution and image quality, measured as a signal-to-noise-ratio, SNR. The result indicates turbulence inßuence, in agreement with the modelling. Different techniques were tested for image quality improvement and the best results were obtained by applying several processing techniques to the images. Moreover, the tests showed that turbulence seriously limits the resolution for horizontal paths close to the ground. A tactical system at 1.5 µm should have better performance than the used 532 nm in atmospheric-limited applications close to ground level. The potential to use existing laser range Þnders and the eye safety issue motivates the future use of 1.5 µm for gated viewing.