Studies Of Observation Mode In Ionospheric Vertical Sounding

After introducing the development history of ionospheric vertical sounding, we combine the features of various modern digital ionosonde, a set of new control and processing programs for Canadian Advanced Digital Ionosonde (CADI) have been developed. Based on this system, several new observation modes in ionospheric vertical sounding are realized, and some practical observation experiments and data analysis are made by using these observation modes. The results reveal that these new observation modes greatly improve the observation capacity and performace of CADI, which is very important to study the ionopheric movement and fine structure.Firstly, the hardware design, entity structure, system ports and software model of CADI are introduced in this paper. Based on CADI system hardware, several new real-time system control and data processing programs for CADI have been developed under Windows 2000 operating system, which has visualization, multitask, network function and good security. These new programs include the CADITEST2K application for system test, the CADIRUN2K application for mode running and data acquisition, the CADIPLOT2K application for off-line displaying and data analysis, and the CADIDEFGEN application for generating mode definition file. The realization of these programs greatly improves the CADI's capacity, maneuverability and usefulness. For example, CADI can perform various tasks such as system control, data acquisition, data analysis, data processing and data display on the same time, which can satisfy the demand of system real-time performance by using multitask capacity of Windows 2000; the system can carry out some functions such as the real-time autoscaling of the measured ionogram data, the real-time transferring and releasing of the data over the internet, and the remote control of the system etc., which make CADI to reach an advanced level of the modern digital ionosondes by using multi-process of Windows 2000. In addition, the system owns the capacity of raw data storing, which can satify the specific demand of ionospheric observation research for the off-line analysis and processing of the raw data. Secondly, several new observation modes in ionospheric vertical sounding have been realized based on the CADI's smart hardware design, the excellent operating system, real-time system control and data processing programs. Doppler ionogram with high precision can be acquired in real time according to echo's phase variation with time. Thus the real-time disturbance observation mode is realized. The realization of real-time disturbance observation mode makes it possible that the precision of Doppler frequency shift is better than 0.1Hz, which can fully satisfy the demand of ionospheric disturbance observation. When two radio frequency pulse signals whose frequency difference is a fixed value are transmitted and the echo's phase difference is measured, the ionospheric virtual height with high precision can be acquired. According to this sounding principle, the observation mode of ionospheric virtual height with high precision is realized. In this mode, the measurement precision of the ionospheric virtual height is increased by more than ten times, that is, from 6 km to about 200 m, which can entirely satisfy the observation research demand of the ionospheric fine structure and small scale disturbance. In passive receiving mode, CADI's transmitter stops working. By using the sacn frequency receiving capacity of the CADI's receivers, radio signals and interferences from space are received within HF band. After processing these received data, the parameter like interference centroid frequency (ICF) can be acquired. Experiments showed that the correlation coefficient between ICF and the ionospheric characteristic parameter foF2 is larger than 0.84. Moreover, the distribution of space interferences'energy with time and frequency can also be obtained for monitoring HF channel of interferences. So the passive receiving mode in CADI provides a useful platform for developing ionospheric passive sounding methods and techniques.Finally, the continuous observation experiments lasting several months are made in Beijing observatory with CADI accompanied with the newly developed system control and data processing programs. By means of the observation data obtained under the ionogram work mode, three large geomagnetic storm events are observed in April, 2006. Throuth scaling and processing these ionogram data, the characteristics during one of the three geomagnetic storm events (from April 13 to 17 of 2006) is studied in detail. In order to study ionospheric disturbances and their propagation caused by the geomagnetic storm, the ionospheric data from other 14 ionosonde stations in East-asia region and the TEC data of the 36 IGS stations provided by international GPS service center and the Jason-1 TEC data provided by American Jet Propel dynamics laboratory are also used. The characteristics of ionoshperic variation and disturbances'propagation in this geomagnetic storm are analyzed in detail, and some explanations and discussions for its possible physical mechanism are also given.