NONLINEAR SIGHTLINE CONTROL

视线系统包括传感器视线的精确目标跟踪、指向和稳定所需的所有子系统和算法。每个系统都集成了从几个已建立的研究领域获得的技术。这项研究提案的战略意图是在英国首次将视线控制作为一个独立的、连贯的研究主题。实现这一目标的第一步是将严格的研究方法应用于两个最重要的视线控制问题/非线性最低点控制和远程成像。航空业受到恐怖行动的经济后遗症的严重打击(如9/11事件后所见)。因此，有必要采用在高风险地区作业时保障飞机安全的技术。被美国国土安全部确定为优先过渡到民用部门的关键军用飞机防御技术之一是定向红外对抗(DIRCM)系统(英国是该技术的重要利益相关者)。这种系统的目的是保护友机免受便携式防空系统(MANPADS)/通常是肩射地对空导弹(SAM)的威胁/通过跟踪来袭来的红外制导导弹，并通过向导弹导引头发送干扰信号来扰乱制导机制。然而，对于摆动的视线系统，存在一个指向角，如果目标通过该指向角，无限速率要求将被发送到其中一个轴。这被称为最低点，并引入了显著的额外跟踪误差，这对飞机来说可能是灾难性的。这个项目的目的是研究几种先进控制算法的适用性，使用预测方法来最小化低谷附近的跟踪误差，从而提高飞机的生存能力。为了获得高分辨率图像，视线抖动被最小化是必不可少的，因为抖动通常是导致图像调制传递函数(MTF)在高空间频率(模糊图像中的细节模糊)滚落的主要因素。抖动可以进一步分解为两个子组，包括由转向系统的机械缺陷(特别是摩擦和振动)引起的视线运动和由大气湍流引起的系统外部的像差。减少机械抖动的控制方案已经得到了很好的研究，例如使用经典的控制、摩擦估计和鲁棒方法，但很少有非线性控制器的活动被记录下来。多年来，天文学界一直使用自适应光学技术，通过测量波前并利用这些信息控制极快的可变形反射镜，来校正图像中的大气扭曲。然而，这种系统的复杂性使它们不适合在空中环境中部署。这里提出的另一种方法是研究非线性控制下的视线抖动与MTF形状之间的映射。由此产生的控制器将首次直接与获得的图像质量相关联，这将使机械抖动的衰减得到显著改善，同时在研究基于图像的大气校正方面迈出第一步。

A sightline system encompasses all subsystems and algorithms necessary for accurate target tracking, pointing and stabilisation of a sensor line-of-sight. Each system integrates technologies obtained from several established research domains. The strategic intention of this research proposal is to develop sightline control as an independent, coherent research topic for the first time in the UK. The first step in achieving this objective is to apply rigorous research methodology to two of the most important sightline control problems / nonlinear nadir control and long-range imaging.The airline industry is severely hit by the economic after effects of terrorist actions (as seen post 9/11). There is therefore a need to adopt technologies that will safeguard aircraft security when operating in high-risk areas. One of the key military aircraft defence technologies identified by the U.S. Department of Homeland Security as a priority transition to the civil sector is the Directed Infra-Red Countermeasures (DIRCM) system (a technology in which the UK is a significant stakeholder). The purpose of such systems is to defend friendly aircraft against the threat posed by Man-Portable Air Defence Systems (MANPADS) / typically shoulder-launched Surface-to-Air Missiles (SAMs) / by tracking the incoming IR-guided missile and confusing the guidance mechanism through delivery of a jamming signal onto the missile seeker. However, for gimballed sightline systems, there exists a pointing angle that, were the target to pass through, infinite rate demands would be sent to one of the axes. This is known as the nadir and introduces significant additional tracking error, which is potentially disastrous for the aircraft. It is the intent of this project to investigate the applicability of several advanced control algorithms, using predictive methods, to minimising tracking error around the nadir and so improve the survivability of the aircraft.To obtain high-resolution images it is essential that sightline jitter be minimised, as jitter is often the dominant contributor to roll-off of the image modulation transfer function (MTF) at high spatial frequencies (blurs-out fine detail in the image). Jitter can be decomposed into two further sub-groups comprising sightline motion introduced by mechanical imperfections in the steering system (notably friction and vibration) and aberrations external to the system introduced by atmospheric turbulence. Control solutions for reducing mechanical jitter have been well researched, using, for example, classical control, friction estimation and robust methods, but very little nonlinear controller activity has been documented. The astronomical community has used adaptive optics for several years to correct for atmospheric distortions in the image by measuring the wavefront and using this information to control an extremely fast deformable mirror. However the complexity of such systems makes them unsuitable for deployment in an airborne environment. The alternative approach proposed here is to investigate the mapping between sightline jitter under nonlinear control and the shape of the MTF. The resulting controllers will, for the first time, be directly coupled to the quality of image obtained, which should see significant improvements in the attenuation of mechanical jitter while simultaneously taking the first steps in researching image-based atmospheric correction.