Design of an adaptive optical wavefront sensor for advanced missile seekers

Precision guided munitions(PGM) including cruise missiles are soon expected to fly with advanced seekers having 2D or 3D imaging capabilities for automatic target recognition(ATR) and terminal guidance against tactical targets. Advanced seekers usually are of dual or multi-mode in nature often with combination of Laser, IR, SAR and MMW imaging capabilities. LWIR and LADAR based electro-optical imaging seekers can provide the highest resolution for classification of tactical targets and thus robust terminal guidance. However the image quality of target scenes is severely affected by the wavefront errors introduced by the inevitable atmospheric turbulence through which light travels from target to seeker. Many other effects including of aerodynamic boundary layers of seeker head and lineof sight jitter are bound to cause wavefront errors particularly when the missile is fast maneuvering to track the target. Though there are tremendous advances in the image processing techniques, it is often complicated and time consuming to reconstruct the actual image by employing these techniques alone without providing real-time compensation for the wavefront errors of these images. Whereas an adaptive optical system in closed-loop operation with multi-actuator deformable mirror and a high resolution wavefront sensor compensates for turbulence and other opto-mechanical effects on the light reaching the receiver of seeker from targets by correcting different wavefront aberrations in real-time. This paper describes the design of integrated adaptive optical wavefront sensor(WFS) for laser and IIR seekers to obtain the high resolution images of target scenes using a MEMS deformable mirror based phase corrector. These wavefront sensors can also provide the much needed accurate line-of sight data for the laser spot seekers of PGMs and also for successful encountering of the active lasers and IRCMs against missiles and aircrafts. The paper also presents comparison among different wavefront sensing techniques for imaging seekers and line-of-sight tracking seekers of PGMs as in the case of semi-active homing guidance. Results of some of our recent experiments for correcting line-of-sight track errors and other higher order wavefront aberrations are also presented here.