焦面拼接反射镜热稳定性对MTF的影响

Influence on MTF of Mirror Thermal Stability in Focal Plane

光学拼接是扩大航天相机视场的有效方法。焦平面采用光学拼接时,拼接反射镜的热稳定性对探测器的共线性和共面性有一定的影响,共线性和共面性误差会引起时间延迟积分电荷耦合器件(TDICCD)的光学调制传递函数(MTF)的下降。文章首先在三维欧式空间建立拼接反射镜热变形前后的平面方程,通过计算TDICCD顶点关于反射镜平面方程的镜像点得出反射镜热变形对TDICCD共线性和共面性的影响;其次,为了对热稳定性进行有效评价,以MTF为其评价函数,分别对TDICCD的共线性误差、共面性误差对TDICCD相机MTF的影响进行了分析,给出了两种误差引起MTF下降的计算公式;最后,以某测绘相机光学拼接焦面为例,对拼接反射镜的热变形引起的探测器的共线性和共面性进行分析,并对不同积分级数下传递函数的下降进行了分析。结果表明,当积分级数为128级时,TDICCD共线性误差引起的飞行方向(X向)MTF下降近似为零,在线阵方向(Y向)MTF下降小于0.025%;共面性误差引起的MTF下降小于0.05%。

The optical butting is an effective technology for broadening view field of camera. During optical butting of focal plane assembly（FPA）, the thermal stability of reflector has effect on linearity and coplanarity. The linear error and coplanar error will cause a decline of the modulation transfer function（MTF）. In this paper, firstly, the plane equation of the reflector before and after the thermal deformation is established in the 3-dimensional Euclidean space. The linear error and coplanar error are calculated by mirroring the CCD vertex. Secondly, in order to evaluate the thermal stability, the MTF is present as the evaluation index. The negative impacts of linear error and coplanar error on TDICCD camera＇s MTF are analyzed. Calculation formulas of MTF caused by the two errors are deduced. Finally, taking an example of a mapping camera, the linear error and coplanar error of the FPA are analyzed. The influence on decline of the dynamic MTF is analyzed with different integral grades. The results prove that the decline of the dynamic MTF caused by linear error is approximately zero in X direction and less than 0.025% in Y direction with an integral grade of 128, and the decline of the dynamic MTF caused by linear error is less than 0.05%.