Image Motion Compensation of Off-Axis TMA Three-Line ArrayAerospace Mapping Cameras

To enhance the image motion compensation accuracy of off-axis three-mirror anastigmatic( TMA)three-line array aerospace mapping cameras,a new method of image motion velocity field modeling is proposed in this paper. Firstly,based on the imaging principle of mapping cameras,an analytical expression of image motion velocity of off-axis TMA three-line array aerospace mapping cameras is deduced from different coordinate systems we established and the attitude dynamics principle. Then,the case of a three-line array mapping camera is studied,in which the simulation of the focal plane image motion velocity fields of the forward-view camera,the nadir-view camera and the backward-view camera are carried out,and the optimization schemes for image motion velocity matching and drift angle matching are formulated according the simulation results. Finally,this method is verified with a dynamic imaging experimental system. The results are indicative of that when image motion compensation for nadir-view camera is conducted using the proposed image motion velocity field model,the line pair of target images at Nyquist frequency is clear and distinguishable. Under the constraint that modulation transfer function( MTF) reduces by 5%,when the horizontal frequencies of the forward-view camera and the backward-view camera are adjusted uniformly according to the proposed image motion velocity matching scheme,the time delay integration( TDI) stages reach 6 at most. When the TDI stages are more than 6,the three groups of camera will independently undergo horizontal frequency adjustment. However, when the proposed drift angle matching scheme is adopted for uniform drift angle adjustment,the number of TDI stages will not exceed 81. The experimental results have demonstrated the validity and accuracy of the proposed image motion velocity field model and matching optimization scheme,providing reliable basis for on-orbit image motion compensation of aerospace mapping cameras.

三线阵CCD立体测绘相机的集成装调

考虑几何精度对三线阵CCD立体测绘相机测绘精度的影响,研究了测绘相机组合体的装调方法以建立和保证相机的空间几何关系。首先,介绍了测绘相机组合体的结构和坐标系的定义;其次,提出了各基准立方镜和相机的装调要求;最后,确定了多相机集成装调流程,重点介绍了测绘相机的装调步骤。装调结果表明:各相机的光学传递函数>0.2,畸变<0.03%,测绘相机的空间几何关系满足要求,提出的集成装调技术有效地保证了测绘相机的空间几何关系。

三线阵CCD立体测绘相机杂光的消除

针对三线阵CCD立体测绘相机的光学系统结构,阐述了杂光的来源和其对相机成像的影响.遮光罩采用碳纤维复合材料,沿着相机的视场角合理设计了挡光片的位置和数量,并喷涂光谱吸收率高达98%的消杂光黑漆;保证透镜安装和装调空间为前提,充分利用支撑筒、压圈和镜框结构,沿着入射光线边缘设计有效的挡光片,结构件整体黑色阳极化处理,支撑筒内壁与镜框和压圈配合区喷涂消杂光黑漆;像面组件除了进行必要的涂层处理外,结构上应避免使用通孔,否则通孔后的非结构件无法进行有效地涂层处理;测绘相机镜头杂光系数检测采用积分球和准直物镜的检测方法,第2批次中3支镜头的杂光系数均低于5%;镜头杂光系数检测结果以及在轨获取的图像情况,表明三线阵CCD立体测绘相机的杂光控制措施得当,基本消除了杂光对相机成像质量的影响,具有一定的工程应用价值.

传输型立体测绘相机的调焦机构设计

提高立体测绘相机地面像元分辨率和地面目标的定位精度,相机需设计调焦环节用以补偿CCD靶面的离焦量。本文根据立体测绘相机光学结构的特点以及相机的焦深,设计了一种基于凸轮导向的调焦机构。在设计中采用了可靠性设计和消空回措施,以保证结构的强度和刚度以及调焦精度。对传动误差的分析及精度验证试验表明:该调焦机构的传动误差为±1.71μm;CCD靶面的直线性精度在X方向为11.2″、Y方向为11.8″;在调焦行程内CCD靶面绕光轴旋转4.7″,满足用户提出的精度要求。

三线阵立体测绘相机构像及误差模型的建立

为了满足立体测绘系统的定位精度要求,在三线阵立体测绘相机研制基础上,通过建立三线阵立体测绘相机实用构像模型,确立被探测地面点在地面坐标系中的坐标与其像点在CCD坐标系中的坐标以及在统一的像平面坐标系中的坐标之间的数学关系式;并在此基础上,推导了三线阵立体测绘实用误差模型,分析影响系统定位精度的主要误差源,并根据相机参数进行综合定位精度分析,结果表明该系统可达到无控定位精度50m的精度要求,同时验证了构像模型及误差模型的正确性。