高精度多普勒频高图的获取和分析

ACQUIREMENT AND ANALYSIS OF HIGH ACCURATE DOPPLIONOGRAM

电离层高频反射回波的多普勒频移是研究电离层扰动的一个重要参数.在数字测高仪探测中,高分辨率的多普勒频移一般在漂移测量中获得,但这种测量方式探测的频点少,不能获得扰动的高度剖面;而在频高图模式下,虽然工作的频点多,能够获得电子浓度的高度剖面的信息,但探测的多普勒频移的分辨率低,无法用来精确检测电离层扰动.实际的电离层高频回波一般为窄带信号,由此本文中提出了一种新的分析方法,利用DGS-256数字测高仪频高图模式下记录的16个多普勒通道的数据,通过反傅里叶变换还原成时域信号,采用最小二乘法估计相邻时间点的相位差,获得高精度多普勒频高图.作为实例,利用该方法分析武汉电离层观象台数字测高仪观测站的观测数据,得到了多频点的多普勒频移曲线.结果表明:在DGS-256数字测高仪频高图模式下能够得到高精度多普勒频高图,这在电离层扰动探测和研究中很有意义.

The Doppler shift of radio wave echoes reflected from ionosphere is an important parameter to observe ionospheric movements. Generally, high resolution Doppler shift could be obtained in drift mode with digital ionosonde. In this mode, only a few working frequencies are used, so ionospheric disturbance profile with height cannot be acquired. However, in ionogram mode, though Digisonde works with many sounding frequencies, the resolution of Doppler shift is too low to detect ionospheric disturbances precisely. In this paper, a new analysis method is given based on the fact of narrow band of ionospheric echoes, through converting sixteen Doppler channel data to temporal domain by IDFT and estimating the phase differences of adjacent time by least square method, the high accurate doppliono-gram could be acquired in ionogram mode. In order to prove the effectiveness of the method, some experiments have been carried out with Digisonde-256 at Wuhan Ionospheric Observatory. The experimental results have revealed that the high accurate Dopplionogram can be acquired, and the present method is very useful in experimental investigation of ionospheric disturbances.