调焦评价函数的性能是影响推扫型遥感卫星星上自动调焦的重要因素。结合敏捷遥感卫星的成像特点和星上处理单元的计算特性,设计了一种敏捷遥感卫星自动调焦策略,提出了一种改进的灰度梯度函数以作为调焦评价函数。该方法在传统灰度梯度函数基础上,结合图像边缘信息与离焦状态的关系,将灰度标准差作为边缘阈值,提取了有效边缘信息并计算图像清晰度。研究结果表明,所提方法具备高灵敏度、强单峰性和良好的时效性,对调焦成像时的场景变化和噪声具有很高的鲁棒性,相比其他常用灰度域调焦评价函数具有明显优势。

The performance of focusing evaluation function is an important factor that affects the on-board autofocusing of a scanning remote sensing satellite. Based on the imaging properties of the agile remote sensing satellite and computing characteristics of the on-board processing unit, an autofocusing strategy of the agile remote sensing satellite is designed, and an improved gray gradient function is proposed as the focusing evaluation function. Based on the traditional gray gradient function and the relationship between image edge information and defocus state, the proposed method takes gray standard deviation as the edge threshold to extract the effective edge information and calculate the image definition. The study results show that the proposed method has high sensitivity, strong unimodality and good timeliness, and is robust to the scene change and noise in the process of focusing imaging. Compared with other commonly used gray scale focusing evaluation function, the proposed algorithm shows obvious advantages.