Study And Application Of Ionospheric Ionogram Conversion

The main result of ionospheric detection is shown in the ionogram,it has been an important target for workers in ionospheric research to obtain the characteristic parameters and electron density profiles in the ionogram.We can roughly understand the change of the structure and the state of the ionosphere according to these parameters,and study the ionosphere deeply.We present a method of converting the ionogram by using the digital image processing technology in order to obtain the characteristic parameters and electron density profiles in the ionograms of Japan.By this way,we analyze the nighttime anomalies of the local ionosphere,and provide a physical explanation of the triggering mechanism.The main contents include:1.A new method for the transform of ionograms was put forward.At first,utilized the Radon transform and the Otsu method to denoise the ionograms.The Components Labeling method was used to enhance the fracture and weakening after denoising.Then,formatted the information of Echo tracing in the ionogram and wrote it into the SBF files where the data could be identified by the SAO Explorer.At last,used the ARTIST algorithm that comes with the software to measure the converted ionograms automatically and obtain the electron density profiles.The image processing and the format conversion process in this method were written as an inonogram processing software.The software was used to statistically analyze the ionogram data in the Okinawa Ionospheric Sounding site,as well as the critical frequency of the of ionospheric F2 layer(f0F2).The results show that this method features high accuracy and efficiency,and it is applicable not only to the batch conversion of ionograms,but also to the conversion of the data and ionogram image which cannot be directly identified by the SAO Explorer.2.The analysis and theory explanations for the nighttime enhancement of the ionospheric electron density.Using the ionogram conversion method,the picture of the ionograms,which were recorded on Wakkanai,Kokubunji,Yamagawa and Okinawa stations in Japan,were processed to acquire the ionospheric parameters and the electron density profile.Based on the acquired ionospheric parameters such as the critical frequency and virtual height of the F2 layer(f0F2 and hmF2),the characteristics for the nighttime enhancement in Japan area have been analyzed,and relative theory explanations have been proposed.In this paper,the pre-midnight and post-midnight enhancement were analyzed respectively.By comparing the occurrence.time of the pre-midnight enhancement observed in the four stations,a latitudinal dependence could be indicated.The higher latitude of the observation sites,the earlier the occurrence time of the pre-midnight enhancement.In other words,the enhancement first appeared in the north of the observation areas,i.e.the Wakkanai station.And then the enhancement moved southward and observed by the Okinawa station last,which located in the lowest latitude of the four stations.Meanwhile,a preliminary explanation for this phenomenon have been proposed.