Gated viewing - initial tests at long ranges

This report describes initial tests with gated viewing at long ranges. The purpose was to study the potential for a system combining an IR camera with a laser camera for target recognition in the range 5-10 km or longer. As camera tubes for 1550 nm were not available, the measurement was done at 532 nm. To extrapolate the results to future system performance at 1550 nm, a theoretical performance model was used which takes into account the camera and atmospheric influence on resolution and image quality. The angular resolution of the camera was 11 grad/lp. The tests showed how turbulence could limit the resolution for horizontal paths close to ground at such short ranges as 2 km. The resolution was then found to be 30-40 mikrorad/lp. During tests at 10 km with a mean height above ground of 60 m, a resolution of 15-40 mikrorad/Ip was obtained. This indicates some turbulence influence. Spatiotemporal processing was proven useful for image quality improvement. Image summation of 5-20 images is recommended for tactical applications, which usually requires motion compensation. Hard- and software based methods for obtaining a homogeneous illumination of the target should also be considered. A tactical system at 1550 nm ought to have better performance than the used 532 nm in atmospheric limited application close to ground. The potential to use existing laser range finders and the eye safety issue motivates the future use of 1550 nm for gated viewing. Until such cameras are available, future tests at 532 nm are motivated to investigate the use of the silhouette and a short gate to get a true 3D resolved target, for verification and further development of the mode and target and background signatures at 1550 nm.