地球同步轨道SAR方位模糊度研究

与低轨合成孔径雷达(SAR)相比较，地球同步轨道合成孔径雷达（GEO SAR）具有重访周期短，观测范围广等优点，在军用及民用领域具有广泛应用。针对地球同步轨道合成孔径雷达多普勒中心频率时变及类滑动聚束工作模式造成常规方位模糊度计算不精确的问题，提出了一种新的方位模糊度计算方法。该方法基于精确的星地几何模型，考虑了地球自转、速度时变、多普勒中心频率时变以及类滑动聚束工作过程中天线指向变化对方位模糊度影响,通过对不模糊区域天线方位角及模糊区域天线方位角的精确求解得到了对应的天线增益值，进而得到方位模糊度的精确值。基于空间坐标系转换及矢量表示法推导了GEOSAR 方位模糊度的表达式。最后结合地球同步轨道SAR轨道参数进行了仿真，验证了该方法的有效性。 

Study on Azimuth Ambiguity for Geosynchronous Earth Orbit SAR

Compared with low orbit Synthetic aperture radar (SAR), geosynchronous Earth orbit Synthetic aperture radar (GEOSAR) has more advantages, such as wider swath, shorter revisiting period, so has a wide range of civil and military applications. Due to the satellite time varying Doppler centroid and analogous sliding spotlight work mode, conventional azimuth ambiguity calculation method is not accurate when used in geosynchronous Earth orbit Synthetic aperture radar. This paper proposes a new method for analyzing the azimuth ambiguity. Based on accurate satellite-earth geometry model, the Earth's rotation, time varying velocity, time-varying Doppler centroid and antenna pointing variance in the analogous sliding spotlight work are considered in the new method. The azimuth ambiguity is obtained accurately when the antenna gains including no ambiguity area and ambiguity area are both calculated. And then the expression of GEOSAR azimuth ambiguity was deduced based on spatial coordinate’s transformation and vector representation. Finally, simulations are carried out to verify the proposed approach using a set of GEOSAR parameters.