电离层电波传播相位污染校正

电离层电波传播相位污染使天波超视距雷达（OTHR）接收的回波信号谱扩展。采用合成孔径雷达（SAR）成像中的相位梯度算法（PGA）来校正相位污染，PGA算法要求所处理的各个分辨单元（这里包括方位和距离单元）具有相同的相位误差，但当对于电离怪空间变化剧烈，或OTHR距离和方位分辨率比较粗时，相邻单元的相位污染不完全相同，这里PGA方法不适用。针对这种情况，考虑相位变化不可能非常剧烈。可用低次多项式表示时，采用最小熵搜索方法，分别校正各单元的电离层相位污染。最后采用我国录取的OTHR实测数据验证，表明这两方法的校正效果良好。

Phase perturbation correction in ionospheric electromagnetic wave propagation

the electromagnetic wave propagation phase perturbation can produce significant spread of the OTHR received echoes.In fact,phase perturbation correction is very similar to autofocus in radar imaging.This paper first utilizes phase gradient autofocus(PGA) algorthm used in synthetic aperture radar(SAR)imaging to correct phase perturbation, but the same phase errors in every resolution cell(including different range cell and different beam)are needed in PGA.This condition can usually be satisfied, but when spatial variation of ionosphere is severe or the resolution of OTHR is 10W,the phase perturbation of neighbor resolution cells may be different, and the PGA is not applicable.For this situaiton, considering that the phase perturbation variation probably is not very severe, sothat it can be approximated by low order polynomial, we adopt the minmurm entropy parameter searching method to correct the phase perturbation of individual resolution cell.These two methods are proved effective by the real dta of China experimental OTHR.