无线电波传播第八讲2电离层中的电波传播.pptx

二、电离层垂直探测
1、探测原理
1) 点为反射点
2) 等量有关
3)
4)
§ 垂直传播中的几个问题
2、频高图
的函数曲线称为频高图。
Ionospheric Station of Gibilmanna
Latitude N XXXX Longitude E
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
This page reports the real time ionograms recorded in Gibilmanna by the new Advanced Ionospheric Sounder (AIS). The critical frequency foF2 and MUF(3000)F2 are scaled by Autoscala program. The AIS and Autoscala were developped at the INGV. This page is updated every 15 minutes.
Characteristics
Each ionospheric layer shows up as an approximately smooth curve, separated from each other by an asymptote at the critical frequency of that layer.
The upwardly curving sections at the beginning of each layer are due to the transmitted wave being slowed by, but not reflected from, underlying ionisation which has a plasma frequency close to, but not equal to the transmitted frequency. For frequencies approaching the level of maximum plasma frequency in a layer, the virtual height tends to infinity, because the pulse must travel a finite distance at effectively zero speed.
The frequencies at which this occurs are called the critical frequencies. The critical frequency of each layer is scaled from the asymptote, and the virtual height of each layer is scaled from the lowest point on each curve
Ionogram’s characteristics
Bottom profile (post-process)
例:设电离层中,对于h > h0 的高度处的等离子体频率为fp2= (h-h0), 是常数,试计算出电离层的虚高h‘,真高hr和相高hp,并比较它们的大小。
相高< 真高< 虚高
三、垂直电离图分析
1、模型法(比较法)
以抛物模型为例。
或
最大电子浓度
最大电子浓度对应的高度
层的半厚度
由推导的结果可得:
以及
即
2、直接积分法
(1)积分反演表达式
(6-38)
(6-39)