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Papers by yixie shao

Ground Based Augmentation System (GBAS) is a version of Differential Global Positioning System (D... more Ground Based Augmentation System (GBAS) is a version of Differential Global Positioning System (DGPS) designed to reliably support airplane's all phase of approach, landing, departure and surface operations. Local ionospheric gradients are major threats to the GBAS, which prevents the advanced use of GBAS. A new monitor for detecting anomalous ionosphere to provide integrity assurance is implemented in this thesis. The monitor is based on the "Fast Initial Response" Cumulative Sum (FIR-CUSUM) quality-assurance method, which is sensitive to the small persistent shifts.

Journal of Geophysical Research: Space Physics, 2018

The Abel inversion method is the classic approach to retrieve electron density profiles from radi... more The Abel inversion method is the classic approach to retrieve electron density profiles from radio occultation measurements, assuming that the electron density is only dependent upon height. In the early 2000s, the total electron content (TEC)-aided inversion method was introduced, where horizontal gradients in the electron density distribution are taken into account by using information from an external model of total electron content (TEC). We show how the quality of the chosen external ionospheric model influences the radio occultation retrievals. Using a two-layer TEC model, the 68% percentiles of the global error distributions of retrieved critical frequency and bottomside ionospheric electron content for 2014 improve more than 30%, with regard to the classic Abel inversion results. In a well-sounded region like Europe, this improvement raises to about 40-45%, while 10% improvement is achieved using two-layer maps with regard to the retrievals using single-layer TEC maps. We point out that using the TEC to describe the horizontal gradient incurs an implicit mismodeling that, until now, has not been taken into account. A new technique is presented that, thanks to TEC modeling by means of two layers, can assess the impacts of such mismodeling. From this technique, a method to select the most accurate radio occultation retrievals is applied to demonstrate that the resulting errors in the retrieved critical frequencies for the European region are smaller than 7% in nearly 82% of the cases, very similar to the relative difference between measurements of two nearby ionosondes.

Remote Sensing

In this study, midlatitude summer nighttime anomalies (MSNAs) are analyzed via observations and t... more In this study, midlatitude summer nighttime anomalies (MSNAs) are analyzed via observations and tidal/planetary wave features using measurements from the Formosat-3/Constellation Observing System for Meteorology, Ionosphere, and Climate (F3C) for 2007, a year with low solar activity, and 2014, a year with high solar activity. The total ionospheric electron content, ECion, an integrated quantity derived from F3C measurements, was used to compare the observational data. The ECion values were derived from accurate radio-occultation-retrieved electron density profiles without assuming spherical symmetry and from a model that separated the ground total electron content into the plasmaspheric and the ionospheric electron content contributions. An analysis of the ECion data set confirmed that MSNAs were present in three different regions of the world for the months surrounding the local summer solstice during both 2007 and 2014. In the southern hemisphere, the so-called Weddell Sea Anomaly...

Lecture Notes in Computer Science

First of all, I would like to give my deepest appreciation to Prof. Guillermo and Prof. Miguel, f... more First of all, I would like to give my deepest appreciation to Prof. Guillermo and Prof. Miguel, for all your patience and support in my study. I am really appreciated to your guidance and encouragement, which gives me the hope and helps me to find a way to carry on the research when I lost my direction. Thanks to your contribution in completing this dissertation. I want to sincerely thank the gAGE group: Prof Jaume, Adria, Deimos, Jesus, Maite. I feel so lucky that I could study and work in gAGE to pursue my degree. With all your help, I gather more knowledge in GNSS and obtain more skills for research. Besides, I spent the lovely time in this group. Furthermore, I am grateful to Estefania Blanch (Observatori de l'Ebre) and Angela Aragon-Angel (Joint Research Center). Thanks for your time and effort in reviewing this work and your precious suggestions. Finally, I would like to give my great thanks to my husband, Albert. All your support and encouragement is really important for me. I am truly appreciated to your companion in the whole way. i 6 Conclusion and Future Work 6.1 Performance of Separability Method (SM) using more accurate GIMs .

Lecture Notes in Computer Science

La recerca feta en aquesta dissertacio consisteix en l'estudi de la ionosfera mitjancant tecn... more La recerca feta en aquesta dissertacio consisteix en l'estudi de la ionosfera mitjancant tecniques d'Ocultacio Radio (RO) de GPS. La primera part s'enfoca en la metodologia d'extraccio de perfils de les mesures RO. L'objectiu es l'obtencio de perfils mes precisos mesurats a partir de les dades. La inversio classica d'Abel es una metodologia emprada ampliament en l'obtencio de RO, tant mateix l'error introduit per l'assumpcio de simetria tambe es reconegut. En ordre d'eliminar aquest error en estudis previs el Separability Method (SM) va ser desenvolupat. En el present treball es revisa i es valida la millora en el metode classic aportada per SM. SM te un millor comportament inclus quan s'exclou l'error de Lack of Collocation (CoL). La precisio dels resultats depenen tambe de l'exactitud del GIM's suportats (p.ex. Com mes exacte son els GIM's emprats millor son els resultats obtinguts). L'error de SM introduit pel mo...

武汉大学学报: 自然科学英文版, 2009

ABSTRACT OSMAR071 is the latest product of the OSMAR (ocean state monitor and analysis radar) ser... more ABSTRACT OSMAR071 is the latest product of the OSMAR (ocean state monitor and analysis radar) series of high frequency surface wave radar (HFSWR), which was developed by the Radiowave Propagation Laboratory of Wuhan University. It adopts a modified Barrick waveheight inversion model. The modifications are introduced to improve the model’s performances under the effect of noises and interferences and in the case of broad beam radar detection. The two unknown coefficients in the modified model are figured out by fitting the HFSWR significant waveheight results to those output from a wave buoy located in the radiating coverage of the radar site. The model is applied to inverse the waveheights from radar data for the duration from Dec. 1st, 2008 to Feb. 25th, 2009, and then the radar waveheights are compared with the buoy measurements. Results show that the rms difference between radar-derived significant waveheights and those from the buoy is 0.38 m and the correlation coefficient between the two series is 0.66. This study describes OSMAR071 observation of significant waveheight with relatively satisfactory accuracy during about three months. Key wordshigh frequency surface wave radar (HFSWR)-OSMAR071-significant waveheight-inversion CLC numberP 716+.22-TN 958.93

2016 International Conference on Localization and GNSS (ICL-GNSS), 2016

Applying a methodology developed and tested in previous studies, the contribution from the ionosp... more Applying a methodology developed and tested in previous studies, the contribution from the ionospheric and plasmaspheric regions to the total electron content (measured by ground receivers) is analyzed. The method is based in the electron density profiles retrieved from radio occultations observed with low Earth orbit satellites, combined with an accurate empirical modeling of the topside-ionosphere electron density. The results of a climatological study of the fractional electron content from the ionospheric region are presented for a year of low solar activity. It is shown that a simple parametric model can be used to reproduce the electron content variations in the ionosphere and the plasmasphere between sunrise and midday, the period of the day showing the largest electron content variability.

Thesis Chapters by yixie shao

The research of this dissertation is studying the ionosphere by GPS radio occultation (RO) techni... more The research of this dissertation is studying the ionosphere by GPS radio occultation (RO) techniques. It is mainly divided into two parts.

The first part focuses on the methodology in profile retrievals from RO measurements. It aims to get more precise profiles from measured data. Classic Abel inversion is a methodology widely used in RO retrievals, and the error introduced by the symmetrical assumption is also well recognised. Separability Method (SM) was developed to eliminate this error in previous studies. In this work, the improvement brought by SM corresponding to classic method is checked and validated. The SM does have better performance excluding the Lack of Collocation (CoL) error. And the precision of the results also depends on the accuracy of the supported GIMs, i.e., the more accurate GIMs is used, the better results could be obtained. The error in SM, introduced by the mis-modelling of using the Vertical Total Electron Content (VTEC) instead of ECLEO, the electron content below LEO height, is also checked. The result shows that it has only minor impact on the retrievals.

The second part is the climatological study of topside ionosphere/bottomside plasmasphere based on the RO retrievals using SM, and aims to give a general picture of characteristics and features of these two regions in different solar periods, 2007 -- solar minimum, and 2014 – maximum. The empirical two-components models of topside profiles, STIP model and CPDH model, used to separate the ionospheric and plasmaspheric contribution of the GPS Total Electron Content (TEC), are studied and validated. And the conditions of applying the STIP model are also discussed. The same as the other empirical models, it shows the picture of topside ionosphere till some limited altitude, which is decided by the Low Earth Orbit (LEO) satellite height.

The model is used to derive transition height hu and scale height hs during these two years. Generally, hu and hs show the clear diurnal, seasonal, solar cycle dependencies.

The concept of IONf, the ionospheric fractional contribution to TEC, is introduced and studied. The ionospheric features are shown and most of the ionospheric anomalies could be checked through this quantity. Compared to the other ionospheric related parameters, such as Ecion and Ecpl, electron content of ionosphere and plasmasphere, IONf is more stable. Hence, it is more suitable for ionosphere modelling. The Capacitor Model is used to model the consistent ‘ionospheric charging process’ during the sunrise sector showing in different circumstance.

Journal of Geophysical Research: Space Physics, 2018

Remote Sensing

Lecture Notes in Computer Science

武汉大学学报: 自然科学英文版, 2009

2016 International Conference on Localization and GNSS (ICL-GNSS), 2016

The model is used to derive transition height hu and scale height hs during these two years. Generally, hu and hs show the clear diurnal, seasonal, solar cycle dependencies.