Study On The Impacts Of Low Latitude Ionospheric Scintillation On The Positioning Performance Of GNSS Receiver

Pseudorange observation and carrier phase observation of GNSS(Global Navigation Satellite System)satellite signals are the basis of GNSS receiver positioning.Ionospheric scintillation can affect the pseudorange observation and carrier phase observation of GNSS receiver.The high-intensity ionospheric scintillation even causes the GNSS receiver to lose lock,resulting in the loss of pseudorange observation data and carrier phase observation data,which seriously affects the positioning performance of the GNSS receiver.Ionospheric scintillation occurs most frequently and is most intense at low latitudes.Regarding the research on the impacts of low latitudes ionospheric scintillation on the positioning performance of GNSS receiver,the work that has been carried out in China and other countries is mainly carried out by using GPS observation data,or in the form of simulation experiments.The vast areas in the south of China are located at low latitudes,which are the high-occurrence areas of ionospheric scintillation.The open service signals of Chinese Beidou satellite system for basic navigation services are similar to other GNSS systems(i.e.,GPS,GLONASS,Galileo,etc.),and they all operate in the L-band with frequencies of 1–2 GHz.With the wide applications of the Beidou satellite system,it is particularly important to study the impacts of low-latitude ionospheric scintillation on the positioning performance of GNSS receiver(especially Beidou receiver).In view of this,this dissertation has carried out related research work.The main work and research results of this dissertation are summarized as follows.Firstly,the processing methods of low-latitude GNSS observation data were studied and the corresponding data processing programs were developed,which laid the foundation for the subsequent work of this dissertation.Secondly,after analyzing multifrequency GNSS ionospheric scintillation observations in Guilin,this dissertation shows that if only the observations of single-frequency GNSS signal are analyzed,other interference phenomena(such as radio frequency interference)may cause large values of the amplitude scintillation index S4 for the received GNSS signal,which may be misjudged as amplitude scintillation event.In order to minimize the impacts of other interference phenomena on GNSS ionospheric scintillation data analysis,the raw signal power(or carrier-to-noise density ratio)observations at multiple GNSS frequencies should be utilized for research.The subsequent work of this dissertation is based on the raw carrier-to-noise density ratio observations of GNSS satellite multifrequency signals during ionospheric scintillation events.Thirdly,using the multi-frequency Beidou satellites observations provided by the Hong Kong Satellite Positioning Reference Network in 2022,the impacts of low-latitude ionospheric scintillation on the pseudorange observations and carrier phase observations of GNSS receivers were studied respectively.The research results are summarized as follows.(1)The strong ionospheric scintillation(namely,amplitude scintillation of S4≥0.5)will cause long-lasting continuous pseudorange observations loss for the GNSS satellite frequency signals received by the GNSS receiver,and the pseudorange observation of satellite signal with lower frequency is more seriously affected by ionospheric scintillation,which significantly reduces the number of GNSS satellites with pseudorange observation data at the corresponding observation time.In low-latitude regions,among the three types of Bei Dou satellites(i.e.,GEO satellites,IGSO satellites,and MEO satellites),the phenomenon of missing pseudorange observations from GEO satellites during ionospheric scintillation is the most severe.The aforementioned impacts of low-latitude ionospheric scintillation on the pseudorange observations of GNSS receiver have nothing to do with the type of receiver and the type of receiver antenna.(2)The stronger the ionosphere scintillation intensity,the longer average missing time of pseudorange observation by GNSS receiver.Weak ionospheric scintillation(namely amplitude scintillation of S4<0.5)at most can cause the phenomenon of missing several seconds pseudorange observations which GNSS receivers occasionally occurs.Strong ionospheric scintillation can cause the phenomenon of missing long-lasting(up to tens of seconds)pseudorange observations which the GNSS satellite signals received by the GNSS receivers occur.(3)The strong ionospheric scintillation can cause long-lasting continuous carrier phase observations loss for GNSS satellite frequency signals received by the GNSS receiver,and the carrier phase observation of satellite signal with lower frequency is more seriously affected by ionospheric scintillation,which makes the number of GNSS satellites with carrier phase observations significantly reduces at the corresponding observation time.In low-latitude regions,among three types of Bei Dou satellites(i.e.,GEO satellites,IGSO satellites,and MEO satellites),the phenomenon of missing carrier phase observations of GEO satellites during ionospheric scintillation is the most severe.The aforementioned impacts of low-latitude ionospheric scintillation on the carrier phase observations of GNSS receiver have nothing to do with the type of receiver and type of receiver antenna.(4)The stronger the ionosphere scintillation intensity,the more frequent the phenomenon of carrier phase cycle slips and carrier phase observations loss in the GNSS receiver.Weak ionospheric scintillation usually does not cause carrier phase cycle slips and carrier phase observations loss in GNSS receiver.Strong ionospheric scintillation can cause frequent carrier phase cycle slips and carrier phase observations loss in GNSS receiver.(5)The stronger the ionosphere scintillation intensity,the longer average missing time of carrier phase observations by GNSS receiver.Weak ionospheric scintillation at most causes the phenomenon of missing several seconds carrier phase observations which GNSS receivers occasionally occurs.Strong ionospheric scintillation can cause he phenomenon of missing long-lasting(up to tens of seconds)carrier phase observations which the GNSS satellite signals received by the GNSS receivers occur.Fourthly,the Tonga volcano eruption at 4:14:45 UT on 15 January 2022 was the most powerful volcanic eruption event since 1883.Afer analysing the Beidou satellite observations of the GNSS multifrequency ionospheric scintillation receivers installed at Guilin and 29 GNSS receivers installed in geographic longitudes from 90°E to 180°E and geographic latitudes from-30°N to 40°N from 12 to 17 January 2022(i.e.,6 days which include the days before the Tonga volcanic eruption,the day of the eruption and the days after the eruption),the dissertation found that,on 15 January 2022,afer the Tonga volcanic eruption,the nighttime ionospheric scintillation events that rarely occurred in January were observed in the vast middle and low latitudes of the Asia-Pacific region.These ionospheric scintillation events led to the phenomenon of missing pseudorange observations and carrier phase observations of multiple GNSS receivers far away from the center of Tonga volcanic eruption,and satellite signal with lower frequency was more seriously affected by ionospheric scintillation.But,on 12-14,16 and 17 January 2022(i.e.,before and after the eruption of Tonga volcano),no ionospheric scintillation events were observed by the 30 GNSS receivers mentioned above.The above studies show that major geographical disaster events such as volcanic eruptions may cause ionospheric scintillation events in vast areas far away from the event location,resulting in serious seriously adverse impacts on pseudorange observation and carrier phase observation of GNSS receiver deployed in these areas.The work of this dissertation not only deepens people’s understanding of the impacts of ionospheric scintillation on GNSS satellite signals,but also provides important basic information for further research on the methods of mitigating the impacts of ionospheric scintillation on the pseudorange observation and carrier phase observation in GNSS receivers and the development of GNSS receiver(especially Beidou receivers)suitable for ionospheric scintillation high-occurrence areas.