The Study On The Loss Of Lock Of GNSS Satellite Signal From Ground-based Observations At The Mid-latitude Region In China

The Earth’s ionosphere is a partially ionized region of space about 60-1000 km above the earth’s surface,which is of great significance to the application of high technology such as radio communication,navigation and positioning,and over-the-horizon radar detection.However,when the satellite signal passes through the ionosphere,its amplitude and phase may change rapidly and violently,which is called ionospheric scintillation.When the flicker is serious,it can even cause signal interruption,leading to the satellite signal can not be locked,that is loss of lock of signal.Ionospheric scintillation and loss of lock of signal have many adverse effects on radio wave propagation,and seriously affect the accuracy of communication,navigation,positioning and over-the-horizon radar detection.Previous researches on loss of lock of signal mainly focused on the low-latitude and high-latitude areas observed by space-based or partial ground-based observation and during magnetic storms,while less attention was paid to loss of lock of signal in mid-latitude areas,especially from the ground-based equipment in mid-latitude.Previous studies have shown that loss of lock of signal mainly occurs in low and high latitudes,but rarely in middle latitudes.Whether that is true still needs further study.Most of China is located in the middle latitude region,so it is necessary to further understand the distribution characteristics and formation mechanism of loss of lock of signal in this region.In this paper,three GNSS ionospheric TEC and scintillation monitors at Chashan station(122.296°E,36.866°N)and Majashan station(122.06°E,37.54°N)have been used to systematically study the phenomenon of loss of lock of signal over the Shandong Peninsula.Firstly,the typical signal lock-out events in middle latitude region of China are analyzed and the criteria are given.Then,the spatial and temporal distribution characteristics of signal lock-out in middle latitude region are summarized comprehensively.Finally,the causes of signal lockout and ionospheric scintillation in middle latitude region are explored.The main research results of this paper are as follows:1.It is found that there are many signal-loss events in middle latitude region,and the typical events are analyzed.This paper analyzes the typical signal lock-out events of GPS,Beidou,etc.It is found that the signal lock-out phenomenon also occurs in the middle latitudes of China,and before the signal lock-out,there are typical characteristics such as the increase of scintillation index,the decrease of signal-to-noise ratio,and the continuous occurrence of many times in a short time,which may be related to the local variation of ionospheric physical parameters in mid-latitude region.Based on the analysis of these events,we put forward the criteria of loss of lock of signal,which lays a foundation for further statistical work of loss of lock phenomenon.2.The temporal and spatial distribution characteristics of loss of lock of signal in middle latitude region are analyzed.The temporal and spatial distribution characteristics of beidou and GPS satellite signal lock-out events of GNSS receivers at Weihai Chashan station and Majashan station are analyzed statistically.It is found that the signal loss mainly occurs in the coastal areas of central and northeastern China between 119°-123°E and 34°-39° N,and less in the inland areas.These events are short in duration,with a maximum duration of 1-2 minutes,followed by 3-6 minutes.The UT distribution trend of observed events at Chashan station and Majashan station is basically the same,but the number of Chashan station(76 events from 2017 to 2021)is less than that of Majiashan station(130 events from 2020 to 2021),this may be because Majashan station is located in the urban area and is subject to more electromagnetic interference.Of the 130 events at Majashan station,more occurred at sunrise(21:00:00UT)and sunset(10:00:00-13:00:00UT)than at any other time,while in the 76 events of Chashan station,there were many events occurring between 0:00:00-1:00:00UT.The number of signal loss events is mostly in autumn and winter,but the peak value of Majiashan station is in July/August,which may be due to the fact that this period is the peak tourist season in Weihai city and there are many man-made disturbances.The number of events increased year by year from 2018 to 2021,which may be related to the enhanced solar activity.In all the events observed by Chashan station,the number of events on BDS was higher than those on GPS satellites,but there was no such difference at Majiashan station.3.The possible causes of signal lock-out are explored,the rapid decrease of ionospheric plasma density may directly lead to loss of lock of signal.Using Madrigal TEC data,GEO stationary satellite TEC data and in-situ plasma data from Zhang Heng-1 satellite,it is found that TEC gradient near the lock-out location is large when the lock-out occurs,and TEC decreased by about 0.2 TECu before loss of lock occurs,and TEC almost reached its minimum value when loss of lock occurs in some case.There is a good correlation between the ionospheric S4 index and electron density(△Ne),indicating that the ionospheric scintillation and even signal loss are caused by the ionospheric density inhomogeneity,the rapid decrease of ionospheric plasma density may directly lead to loss of lock of signal.When the ionospheric density disturbance becomes calm,the signal lock-out disappears.In this paper,the phenomenon and causes of loss of lock of signal in middle latitude region of China are systematically studied.The results are helpful to understand the spatial and temporal distribution characteristics and formation mechanism of satellite signal lock-out in middle latitude region,and will be applied to modeling and forecasting ionospheric and scintillation,providing scientific basis for improving the accuracy of satellite communication and navigation and over-the-horizon radar detection.