Instantaneous Filed of View (IFOV) is a key parameter for space-based infrared point target detection system. An appropriate IFOV should be selected for a caliber limited space camera to achieve high SNR. The influence of IFOV on energy concentration, sampling phase factor, background clutter and SNR is discussed for a diffraction limited system. An IFOV optimization model is proposed to achieve the maximum SNR. Clutter quantification is executed based on background images, and then clutter coefficient range and distribution are gained. A simulation is conducted based on the model and example parameters. Conclusions are obtained as follows: decrease of IFOV results in energy concentration falling, detection stability getting better and clutter fading down. SNR increases at first and then decreases as IFOV getting smaller. An optimal IFOV is found in the end. The proposed model can be applied to parameter design and optimization of space camera.%瞬时视场是影响星载红外点目标探测系统性能的重要指标,为了实现高信噪比探测,有限口径的空间相机设计需要选择合适的瞬时视场.文章讨论了衍射受限条件下,瞬时视场对能量集中度、采样相位因子、背景杂波和信噪比的影响,建立了以信噪比最大化为目标函数的瞬时视场优化模型.基于在轨遥感图像统计背景杂波,确定了杂波系数范围和不同杂波程度的背景分布.结合实例仿真,计算了不同瞬时视场下的信号响应和信噪比变化,通过分析得出结论:随着瞬时视场减小,点目标能量集中度降低,采样相位影响减小,探测稳定性提高,杂波减小,信噪比先增大后减小,利用优化模型能得到最优瞬时视场.文章提出的模型可用于空间相机的指标设计和优化.
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