基于JPL星历的月基SAR多普勒参数估算方法

月基合成孔径雷达(SAR)与传统低轨SAR相比,成像几何上存在成像距离长的特点,其多普勒参数估计方法也不同于常规的机载和星载SAR.基于喷气推进实验室(JPL)高精度星历,可以通过插值获取月心在地心惯性坐标系下的位置、速度和加速度以及月球天平动,然后经由坐标转换得到月面任意位置在地心惯性坐标系下的位置、速度和加速度.在此基础上,建立了两个二次方程组,第1个方程组的解表示任意星下点离线角和斜视角情况下的波束矢量,第2个方程组求得波束矢量的模值,以此解算地面波束中心的坐标.结果表明,月基SAR的波束角需沿轨不断调整,而且天线放置的位置也会对多普勒参数产生明显影响.

Method to estimate the Doppler parameters of moon-borne SAR using JPL ephemeris

Compared with the low earth orbit synthetic aperture radar (SAR) system, the moon-borne SAR is distinct from its unique imaging geometry, so the Doppler parameters estimation method is different from conventional pickaback and satellite-borne SAR. Precise jet propulsion laboratory (JPL) ephemeris was used to interpolate the position, velocity and acceleration of lunar barycenter as well as the libration in geocentric inertial coordinate system. Then the position, velocity and acceleration of an object at any selenographic coordinates were able to be acquired via the coordinate transformation. Based on this, two quadratic equation sets were put forward to calculate the beam direction at any off-nadir angle and squint angle, and to solve the modulus value of line of sight, then coordinating the footprint center. Simulation results show that the beam angle needs a continuous adjustment along the orbit to point the earth disk in moon-borne SAR case, and the antenna position displacement leads to a significant shift on the Doppler parameters.