Dual-mode seeker with imaging sensor and semi-active laser detector

When the field of operation of precision strike ground/air-to-ground missiles is extended to beyond-line-of-sight missions, autonomous seekers will soon encounter serious difficulties, especially with regard to low signature targets and complex scenarios. We have investigated dual-mode sensors which are conceived to overcome these specific problems by combining an imaging sensor with a semi-active laser seeker. These sensors offer non-line-of-sight target engagement with high reliability and under operator control using a laser target designator while minimizing the active exposure time for target designation by handing over the tracking process, once the passive imaging sensor has locked onto the target. For this purpose a laboratory demonstrator has been built with a standard TV-sensor and an InGaAs 4-quadrant detector mounted on a 2-axes gimbal system. Both detectors use a common objective; the focussed radiation is divided by a spectral beam splitter. The signals of the 4-quadrant detector are digitized and subsequently processed by an FPGA. If the pre-programmed laser pulse characteristic is identified, the position information is evaluated and the gimbal system activated in order to center the laser spot. Subsequently a tracker locks onto the target signature found in the imaging sensor signal. Once lock-on is confirmed the laser can be turned off automatically. We present the results of laboratory and field tests obtained with the dual-mode demonstrator. Based on these results we plan to replace the TV-sensor by an uncooled microbolometer array in the future. The design and expected performance of such a dual-mode sensor will be discussed. Keywords: dual-mode sensor, semi-active laser seeker, microbolometer array, target engagement