Research On Location Technology In The Ionospheric Sounding System

The ionosphere, which is the medium for the shortwave propagation, increases the difficulty of target location because of the time-varying characteristics. With the ionospheric sounding system, the research on the relative target location technology, which is developed for solving time-varying characteristics of the ionosphere, can make full use of the radar sounding equipments and technologies. Wuhan Ionospheric Sounding System (WISS), whose operating frequency is3-30MHz, has been developed by the Ionosphere Laboratory of Wuhan University since2001. The system has several advantages such as small size, low power consumption with strong mobility, etc. And its hardware and software facilities are updated continuously to meet various demands. Hence, it can be used as a powerful tool to make ionospheric sounding, and its own characteristics can be applied for many other domains as well, such as target reconnoitering, monitoring electromagnetic environment, short-wave channel management, earthquake prediction, etc. In this thesis, as the result of the problem of extended wide, fuzzy mode, multipath effect and so on, some specific algorithms research have been carried out as well as some corresponding technology research. And the technology research covers several domains, such as the aircraft location technology, the ionospheric irregularities location technology, the one-dimensional location technology of shortwave single station, the two-dimensional location technology of shortwave single station and so on. Experiments have also been carried out to validate the methods and the practicability of WISS. The main research results are presented as follows:1. The Neural Network and Time Frequency (NNTF) joint algorithm is presented in this thesis.Since the ionosphere varies temporally and spatially, severe multipath effects which jeopardize the characteristic quantities extracting of targets from the recorded data are produced. To solve the above problems and further identify the targets from the fuzzy signals, a Neural Networks and Time-Frequency (NNTF) based on algorithm is presented in this thesis. By neural networks, the characteristic quantities of targets are extracted from the recorded data. Then, the Doppler spectrum of target signals is computed to determine the radial velocity of targets. Moreover, with the help of Time-Frequency analysis, the radial velocity variability in time domain, which finally leads to the identification of the type of the targets, can be identified, Simulations using the recorded data of the WISS show that the type of the targets is aircraft and90.9%accurate recognition of aircraft targets can be achieved.2. The genetic iterative algorithm based on the distance information is presented in this thesis to locate the ionospheric irregularities body.With the ionospheric sounding system, the ionospheric irregularities body location technology has been carried out. Since the drawback of direct method based on the distance information is low sensitivity in the echo-signal-group path and instable performance, the genetic iterative algorithm based on the distance information is presented in this thesis. With the multi-base detection, the group path of ionospheric irregularities body could be obtained. Jointing the distance information and the group path of each site, the longitude, the latitude and the altitude of the ionospheric irregularities body could be worked out by the objective function of the genetic iterative algorithm. A new idea is presented for the study of ionospheric irregularities body location.3. The CAPON and ROOT-MUSIC (CRMU) joint algorithm is presented in this thesis.With the ionospheric sounding system, the one-dimensional location technology of shortwave single station has been carried out. Due to the deficiencies which is low sensitivity of beam field and noise-sensitive of high resolution spatial spectrum algorithm, the CAPON and ROOT-MUSIC (CRMU) joint algorithm is proposed in this thesis to research the one-dimensional location technology. The CRMU algorithm could avoid the peak search and suppress the noise in order to reduce the Root Mean Square Error (RMSE) of azimuth. The RMSE of the CRMU algorithm is at least0.2degrees smaller than that of the ROOT-MUSIC algorithm. Based on the one-dimensional location of shortwave single station, the location error of the CRMU algorithm is less than3%, which meets the demand that the loaction error should be below5%.4. The improved algorithm is presented in this thesis to solve the problem of elevation angle spread.With the ionospheric sounding system, the two-dimensional location technology of shortwave single station has been carried out. Since the ionosphere varies temporally and spatially, severe multipath effects which cause the elevation angle spread are produced. With the time accumulation, this improved algorithm, which is based on the two-dimensional MUSIC algorithm, could compensate for the random instability of the elevation angle. With the fuzzy clustering algorithm and the azimuth filtering, this improved algorithm could make the spread elevation angle values concentrated by making full use of the space-time statistics. Elevation angle values obtained by the improved algorithm are focused, which shows that the improved algorithm has good performance. Based on the two-dimensional location of shortwave single station, the location error of the improved algorithm is less than7%, which meets the demand that the location error should be below10%.