基于地球椭球的离轴式双线阵相机像移补偿

Image motion compensation of off-axis two-line camera based on earth ellipsoid

离轴反射式双线阵立体测绘相机的视轴和光轴分离,由于地球为椭球体,视轴和光轴对应的地物点的距离随星下点与升交点的地心角而变化。而成像传感器与光轴垂直,对视轴对应的地物点成像,这些因素导致离轴反射式双线阵立体测绘相机的像移速度和偏流角随离轴角等变化。在对离轴反射式空间相机的成像原理进行分析的基础上建立其等效简化模型,推导了基于地球椭球的离轴反射式双线阵立体测绘相机的像移速度和偏流角计算公式。并以某离轴反射式双线阵立体测绘相机为例,对正视相机和后视相机统一调整行周期与偏流角对成像质量的影响进行分析。分析结果表明,以调制传递函数下降不超过5%为约束,当积分级数大于4时应分别调整正视相机和后视相机的行周期。统一调整偏流角时应以正视相机和后视相机偏流角的均值为准,积分级数应取89以内。

As view axis and optical axis of reflective off-axis two-line stereo mapping camera are separate and the earth is in fact an ellipsoid, distances between objects on earth corresponding to view axis and optical axis vary with geocentric angle from substellar to ascend point. In addition imaging sensor is perpendicular to optical axis while imaging the objects on earth corresponding to view axis. All these factors lead to change of image motion speeds and drift angles along with off-axis angles. Equivalent simplified model of reflective off-axis space camera was established based on analysis of its imaging principle. Formulas of image motion speeds and drift angles of reflective off-axis two-line stereo mapping camera based on earth ellipsoid were deduced. Influence of adjusting row transfer periods and drift angles uniformly on imaging quality of a reflective off-axis two-line stereo mapping camera was analyzed. Results of analysis indicates that if no more than 5% drop of modulation transfer function is used as a constraint, row transfer periods of nadir-view camera and backward-view camera should be adjusted individually as TDI stages is greater than 4. When drift angles are adjusted uniformly, mean value of drift angles of nadir-view camera and backward-view camera should be used and TDI stages should not exceed 89.