针对光电对抗系统在红外小目标被动测距中的不足，提出了一种基于目标距离比和方向信息的被动测距算法. 建立了三维空间中的目标和探测器运动模型，通过数学分析构建估计红外小目标距离的一元二次方程，其参数由相邻采样时刻目标到探测器的距离比、探测器自身空间坐标、目标对探测器的方位角及高低角决定. 通过仿真实验和加噪分析验证了该方法的有效性. 文中所提方法表达简单，可避免分母接近于零的情况，适用于机载或弹载双波段红外探测器对小目标的距离估计.

 To overcome the problems in passive ranging of infrared small targets used in photoelectric countermeasure
systems, a passive ranging scheme is proposed based on the distance-ratio between two adjacent
sampling times and the direction information about the azimuth and pitch angles of the target. A model of
motion is build to describe the relative position between the observer and the target in a 3D space. With
this model, a quadratic equation is derived, whose parameters can be calculated by using the distance-ratio,
the 3D coordinates of the observer, and the azimuth and pitch angles of the target. The proposed method
has a simple form, and can avoid the occurrence of near-zero values in the denominator. The performance is
demonstrated by simulation. It is applicable to the estimation of the target distance with a dual-band infrared
detection system installed on an airborne or missile-borne platform.