The characteristics of anomalous radio propagation in the frequency 1 - 30 MHz before and after the 2011 Tohoku-Oki earthquake are firstly revealed by using oblique ionograms for the pass from Wakkanai to Kokubunji wh...The characteristics of anomalous radio propagation in the frequency 1 - 30 MHz before and after the 2011 Tohoku-Oki earthquake are firstly revealed by using oblique ionograms for the pass from Wakkanai to Kokubunji which is closest to the epicenter. An oblique ionogram with a wavy-shape-trace was observed at 06:30 UTC on 11 March 2011 after the 2011 Tohoku-Oki earthquake. The velocity of northward-propagating disturbance caused this wavy-shape-trace is estimated to be 130 m/s. This wave-shape-trace shows very clear signature appearing in the oblique ionograms as the characteristic of strong ionospheric disturbances triggered by the earthquake. An oblique ionogram with a steep slopy-shape-trace was observed at 04:45 UTC on 11 March 2011 one hour before the 2011 Tohoku-Oki earthquake. This slopy-shape-trace is investigated as the signatures of preseismic ionospheric anomaly. This anomalous oblique ionogram with a slopy-shape-trace is examined with the slope ratio of virtual height to sweep-frequency, and the difference between monthly median foF2 and hourly value foF2 at Wakkanai and Kokubunji. These features appearing in oblique ionograms suggest that it is useful for studying the signatures of preseismic ionospheric anomaly.展开更多
The vertical ionogram can provide the important ionospheric parameters, such as critical frequency, virtual height and electron density, for ionospheric research. The oblique ionosonde has the ability to detect the io...The vertical ionogram can provide the important ionospheric parameters, such as critical frequency, virtual height and electron density, for ionospheric research. The oblique ionosonde has the ability to detect the ionosphere over sea and other terrain where it is not practical to deploy vertical sounder and provide more ionograms with less transmitting and receiving devices. Therefore, the conversion of the oblique ionogram to vertical ionogram for obtaining the important ionospheric parameters is a very useful inversion technology. The experimental comparison between oblique and vertical detections was carried out in the equatorial ionospheric anomaly (EIA) region of south China on 25 and 26 August 2010. The oblique detecting path was from Wuhan to Shenzhen and the VI ionosonde was located in the midpoint of the oblique path. The oblique ionogram reversion results showed a small deviation of the critical frequency, minimum virtual height as well as the electron density profile of the ionospheric F layer, as compared with the real vertical observations.展开更多
The Mars Advanced Radar for Subsurface and Ionosphere Sounding(MARSIS) onboard the Mars Express(MEX) spacecraft started to collect data of the Martian topside ionosphere from May,2005.By now a large amount of ionogram...The Mars Advanced Radar for Subsurface and Ionosphere Sounding(MARSIS) onboard the Mars Express(MEX) spacecraft started to collect data of the Martian topside ionosphere from May,2005.By now a large amount of ionograms has been obtained.It is important to extract vertical ionospheric information effectively from the ionograms for further study.In this paper a new method,Object Tracking Method(OTM),is proposed to automatically extract the ionospheric electron density profiles by computer.This method is based on three algorithms,namely the Hough transform,region growing segmentation algorithm and moving objects detection method from video sequences.In processing ionosphere echoes are treated as moving objects.The identification ratio of OTM for the MARSIS ionograms is estimated to be around 90%.展开更多
Automatic scaling ionogram can get the parameters of ionogram which are vital to ionosphere detecting. In this paper, a new method is proposed to scale F2 layer trace automatically from oblique ionogram based on morph...Automatic scaling ionogram can get the parameters of ionogram which are vital to ionosphere detecting. In this paper, a new method is proposed to scale F2 layer trace automatically from oblique ionogram based on morphological operator and inversion technique. This method is verified through the comparison of actual detecting data with statistical analysis. The results show that the proposed automatic scaling method has high acceptable rate and is suitable for scaling oblique ionogram with different high angle wave states. It is fast and precise to fit O-mode echoes in F2 layer without the influence from F1 layer. This method could be applied in real-time ionospheric oblique sounding research with high reliability and versatility.展开更多
文摘The characteristics of anomalous radio propagation in the frequency 1 - 30 MHz before and after the 2011 Tohoku-Oki earthquake are firstly revealed by using oblique ionograms for the pass from Wakkanai to Kokubunji which is closest to the epicenter. An oblique ionogram with a wavy-shape-trace was observed at 06:30 UTC on 11 March 2011 after the 2011 Tohoku-Oki earthquake. The velocity of northward-propagating disturbance caused this wavy-shape-trace is estimated to be 130 m/s. This wave-shape-trace shows very clear signature appearing in the oblique ionograms as the characteristic of strong ionospheric disturbances triggered by the earthquake. An oblique ionogram with a steep slopy-shape-trace was observed at 04:45 UTC on 11 March 2011 one hour before the 2011 Tohoku-Oki earthquake. This slopy-shape-trace is investigated as the signatures of preseismic ionospheric anomaly. This anomalous oblique ionogram with a slopy-shape-trace is examined with the slope ratio of virtual height to sweep-frequency, and the difference between monthly median foF2 and hourly value foF2 at Wakkanai and Kokubunji. These features appearing in oblique ionograms suggest that it is useful for studying the signatures of preseismic ionospheric anomaly.
基金supported by the National Natural Science Foundation of China (Grant Nos. 40804042 and 41074115)the Post Doctor Foundation of China (Grant No. 200902445)the Fundamental Research Funds for the Central Universities (Grant No. 4081004)
文摘The vertical ionogram can provide the important ionospheric parameters, such as critical frequency, virtual height and electron density, for ionospheric research. The oblique ionosonde has the ability to detect the ionosphere over sea and other terrain where it is not practical to deploy vertical sounder and provide more ionograms with less transmitting and receiving devices. Therefore, the conversion of the oblique ionogram to vertical ionogram for obtaining the important ionospheric parameters is a very useful inversion technology. The experimental comparison between oblique and vertical detections was carried out in the equatorial ionospheric anomaly (EIA) region of south China on 25 and 26 August 2010. The oblique detecting path was from Wuhan to Shenzhen and the VI ionosonde was located in the midpoint of the oblique path. The oblique ionogram reversion results showed a small deviation of the critical frequency, minimum virtual height as well as the electron density profile of the ionospheric F layer, as compared with the real vertical observations.
基金supported by the National Natural Science Foundation of China(Grant Nos. 10973031,2008AA12A210 and 2010AA122206)
文摘The Mars Advanced Radar for Subsurface and Ionosphere Sounding(MARSIS) onboard the Mars Express(MEX) spacecraft started to collect data of the Martian topside ionosphere from May,2005.By now a large amount of ionograms has been obtained.It is important to extract vertical ionospheric information effectively from the ionograms for further study.In this paper a new method,Object Tracking Method(OTM),is proposed to automatically extract the ionospheric electron density profiles by computer.This method is based on three algorithms,namely the Hough transform,region growing segmentation algorithm and moving objects detection method from video sequences.In processing ionosphere echoes are treated as moving objects.The identification ratio of OTM for the MARSIS ionograms is estimated to be around 90%.
基金Supported by the National Natural Science Foundation of China(59975035,41006058)the Fundamental Research Funds for the Central Universities(2014212020205)
文摘Automatic scaling ionogram can get the parameters of ionogram which are vital to ionosphere detecting. In this paper, a new method is proposed to scale F2 layer trace automatically from oblique ionogram based on morphological operator and inversion technique. This method is verified through the comparison of actual detecting data with statistical analysis. The results show that the proposed automatic scaling method has high acceptable rate and is suitable for scaling oblique ionogram with different high angle wave states. It is fast and precise to fit O-mode echoes in F2 layer without the influence from F1 layer. This method could be applied in real-time ionospheric oblique sounding research with high reliability and versatility.
