嫦娥三号探测器系统两器分离是着陆后进行的第一个关键动作，也是后续着陆器探测和巡视器月面巡视勘察的基础，解决两器安全分离问题对于整个工程的实施具有重要意义。针对实际任务中对分离决策实时性和可靠性要求高的特点，使用基于着陆器监视相机的单像量测方法对月面环境中障碍物和通信遮挡包络进行分析计算，评估两器分离过程中的不安全因素，为两器分离决策提供支持。介绍了监视相机单像量测和通信遮挡包络计算方法，并对量测精度进行了分析验证。

Chang'e-3(CE-3) mission, which includes China's first lunar lander and rover, was successfully soft landed on the Moon on December 14, 2013. After landing, the separation of the rover and the lander is a critical step of the mission operation, and is also the basis for subsequent explorations by the lander and the rover. As there exist terrain obstacles and communication blackout, it is important to calculate parameters of obstacles and communication envelope, which will be helpful for rover to avoid obstacles and drive smoothly after separation.To satisfy the requirements of fast and reliable decision making for rover-lander separation, we performed monoscopic measurements of the obstacles and calculated the communication envelope based on an image acuired by the monitoring camera. (1) We define three coordinate systems including rover body coordinate system, local coordinate system and monitoring camera coordinate system. These coordinate systems can be transformed to each other by matrix operations according to landing attitudes, rotation matrices and translation vectors. (2) Through coordinate system transformation, object coordinates can be calculated from image corodinates by using collinearity equations. In particular, sizes of the obstacles (e.g., rocks) and distances to the lander are caculated and labeled on the image. (3) Projection transformation is applied to obtain the communication envelope.The monoscopic measurement method developed in this paper is verified with a Digital Ortho Map (DOM) of 2 mm resolution, which is generated by Navcam stereo images. The measurement accuracy is obtained by comparing monoscopic measurement results with ground truth, which is dervied from obstacle size measurement on the Navcam DOM. Experimental results show that the measurement error in object space is less than 10% and can meet the requirements of decision support.These measurements contributed to evaluation of terrain obstacles and communication blackout directly. The proposed method was successfullly used in CE-3 mission to support decision making for rover-lander separation.