Time-dependent 3D Ionospheric Tomography And Its Applications

The ionosphere has a close relation with the human activities.It has the seriously influence on shortwave communication,space activities,positioning precision of Global Positioning System(GPS),and so on.Total electron content(TEC)is an important physical parameter for understanding temporalspatial variations of the ionosphere.TEC model is usually based on the single-thin layer assumption,so TEC can only reflect the horizontal structure of the ionosphere.Computerized ionospheric tomography(CIT)technique is suitable for getting three-dimensional(3D)ionospheric electron density.However,the traditional ionospheric tomography is mainly carried out at the specific moment.If involved the states of electron density at different time or given the improper prior value,it may need a large amount of calculation and have a low efficiency.Therefore,3D time-dependent ionospheric electron density over China is inverted by Kalman filter tomography's algorithm.The GPS data is obtained from the Crustal Movement Observation Network of China(CMONC).The main task in this thesis is summarized as follows:1.CIT theory is discussed systematically.To resolve the defects of traditional ionospheric tomography,an algorithm of ionospheric tomography is proposed in this article based on Kalman filter.The ionospheric electron density over China on a quiet day is inversed.The result shows the evolution of the electron density during a day.At last,compared with the data from the ionosonde,it is proved that the new method is reliable.2.The 30-day vertical total electron content(VTEC)series derived from ground-based GPS observations is used to examine the ionospheric variations by the sliding window method during the especially big magnetic storm.By the Kalman filter tomographic algorithm,the author gets the ionospheric electrondensity during the big magnetic storm day.The result shows the remarkable variation of the electron density mainly happens in the F layer and the electron density has an obvious increase.It increases by about 66% relative to the quiet day's electron density and reflects the intense positive phase.Compared with IRI model,the result of ionospheric tomography from the Kalman filter algorithm can be better for reflecting the variations of ionosphere.The value of the electron density is compared with the data from the ionosonde.3.An Ms 7.3 earthquake struck Yutian in Xinjiang province on 12 February2014.The abnormal variations of the ionospheric VTEC based on CMONC are identified by the sliding time window.Excluding the influence of solar activity and geomagnetic environment,the author thinks that the abnormal increase of VTEC value on 2th February may be related to the earthquake.Finally,the author uses the Kalman filter algorithm to get the 3D ionospheric electron density.The results not only confirms the abnormal variations,but also reflects the variations of ionosphere in details.