一种基于星载SAR编码有源定标器的电离层TEC测量方法

针对电离层对星载SAR线性调频信号影响与频率有关的特点,结合正负调频率的线性调频信号受电离层影响会出现脉冲信号的压缩和展宽现象,提出了一种基于星载SAR编码有源定标器的电离层TEC测量方法.利用编码有源定标器可以实现调频率反向的功能,通过分析调频率反向和不反向两种信号的相位差以及脉压后的位移差实现电离层TEC的精确测量,该方法不依赖于SAR与有源定标器之间的距离以及SAR发射信号的相位,减小了电离层TEC测量的误差因素,提高了电离层TEC的测量精度.针对BIOMASS,TerraSAR-L以及HJ1C三部不同频段的SAR系统进行了仿真分析,仿真分析结果与理论计算一致,证明了该方法的有效性.

An approach for measuring ionospheric TEC based on coded active radar calibrator of spaceborne SAR

Ionospheric effects such as signal path delays, Faraday rotation （FR） and changes in the length of the transmitted pulse depend on frequency. For a linearly frequency-modulated chirp signal, the frequency-dependent time-delays imply a slight change in the chirp rate and a change in the length of the received pulse. The length of the received pulse will be shortened compared with the transmitted pulse for upchirps and broadened for downchirps. An approach is proposed for measuring the ionospheric Total Electron Content （TEC） based on a coded Active Radar Calibrator （ARC） for a spaceborne Synthetic Aperture Radar （SAR）. The TEC can be deduced from the phase difference and offset in the range between the downchirp and upchirp retransmitted to the SAR by a coded ARC. The method is not dependent on the phase of the transmitted signal and the range between the SAR and ARC, so the precision of TEC measurement can be improved. Simulations are performed for various band spaceborne SAR sensors of the BIOMASS, TerraSAR-L and HJIC satellites. The results from the simulation are in accordance with the theoretical analysis and the validity of the method proposed is proved.