This study analyzes total electron content(TEC)variations during two solar eclipse events that occurred on October 25,2022,and October 14,2023.The solar eclipse of October 25,2022,was a partial solar eclipse,while the...This study analyzes total electron content(TEC)variations during two solar eclipse events that occurred on October 25,2022,and October 14,2023.The solar eclipse of October 25,2022,was a partial solar eclipse,while the eclipse of October 14,2023,was an annular solar eclipse.For this study,the data of eight International GNSS Service(IGS)stations from different eclipse coverage zones are used to analyze TEC variations.It is found that the stations located in the maximum eclipse cover zone exhibited notable decreases in TEC values.The minimum variation of about 11.76%in TEC values is observed at the station situating in about 20 percent eclipse cover zone,while it varies from 22%to 38%at the stations falling in about 60 percent eclipse cover zone.The highest variation in TEC values of about 44%is found at the stations in about 80 percent eclipse cover zone.The time of occurrence of maximum depletion in TEC values at each station is in line with their longitudinal sequence.Atmospheric gravity waves(AGWs)are also observed by performing wavelet analysis on TEC data.The global TEC maps visualize and confirm observed TEC variations,providing spatial and temporal insights into the ionospheric response.This analysis highlights the influence of station location and eclipse coverage on the magnitude and spatial distribution of TEC variations.展开更多
This paper demonstrates that the spatial distribution of the ionospheric TEC over the Indian region can be reconstructed with appreciable accuracy using minimal numbers of empirical orthogonal functions as a basis.The...This paper demonstrates that the spatial distribution of the ionospheric TEC over the Indian region can be reconstructed with appreciable accuracy using minimal numbers of empirical orthogonal functions as a basis.These basis functions were derived using the Singular Value Decomposition of a matrix composed of pragmatic vertical Total Electron Content(VTEC)values collected across varied ionospheric conditions and measured over the region of interest.The reconstruction was achieved by linearly combining the appropriately chosen significant bases with corresponding weight factors.The reconstruction accuracy of the algorithm was found to be better than 4 TECU(TECU=1016electrons/m2)for more than 99.9%of the time when tested over the complete year of 2016 with only eight basis vectors.The containment factor,defined here,indicates the goodness of the chosen bases in representing the arbitrary VTEC distributions and is found to remain typically high,aiding in improved algorithm performance.The performance,however,was found to be sensitive to the seasons and geomagnetic conditions.Deteriorated performance was observed when tested for the St.Patrick's Day storm data.The deterioration was attributed to the structural alteration of the ionospheric plasma density and the presence of atypical modes during the storm.The results ascertain the prospect of a faithful representation of the spatial distribution of the ionospheric VTEC using limited parametric variables,which may find utility in navigation,radar,and various other applications.展开更多
In this study,the gradients of Total Electron Content(TEC)for a midlatitude region are estimated and grouped with respect to the distance between neighboring stations,time periods within a day,and satellite directions...In this study,the gradients of Total Electron Content(TEC)for a midlatitude region are estimated and grouped with respect to the distance between neighboring stations,time periods within a day,and satellite directions.Annual medians of these gradients for quiet days are computed as templates.The metric distances(L2N)and Symmetric Kullback-Leibler Distances(SKLD)are obtained between the templates and the daily gradient series.The grouped histograms are fitted to the prospective Probability Density Functions(PDF).The method is applied to the Slant Total Electron Content(STEC)estimates from the Turkish National Permanent GPS Network(TNPGN-Active)for 2015.The highest gradients are observed in the east-west axis with a maximum of 25 mm/km during a geomagnetic storm.The maximum differences from the gradient templates occur for neighboring stations within100-130 km distance away from each other,during night hours,and for regions bordering the Black Sea and the Mediterranean in the northeast and southeast of Turkey.The empirical PDFs of the stationpair gradients are predominantly Weibull-distributed.The mean values of Weibull PDFs in all station groups are between 1.2 and 1.8 mm/km,with an increase during noon and afternoon hours.The standard deviations of the gradient PDFs generally increase during night hours.The algorithm will form a basis for quantifying the stochastic variations of the spatial rate of change of TEC trends in midlatitude regions,thus supplementing reliable and accurate regional monitoring of ionospheric variability.展开更多
The measurements of very low frequency/low frequency (VLF/LF) signals at the Petropavlovsk-Kamchatsky (PTK) and Yuzhno-Sakhalinsk (YSH) stations in Russia and several observing stations in Japan were used for the anal...The measurements of very low frequency/low frequency (VLF/LF) signals at the Petropavlovsk-Kamchatsky (PTK) and Yuzhno-Sakhalinsk (YSH) stations in Russia and several observing stations in Japan were used for the analysis of lower ionospheric perturbations in possible association with two earthquakes (EQs) which occurred offshore the Pacific Ocean of Japan in November 2016. The first EQ with M (magnitude) = 6.1 (depth 42 km) happened close to the coast line on 11 November (UT). The second EQ was recorded in the sea on 21 November (UT) with M = 6.9 (depth 11 km) and they had a series of aftershocks with M up to 5.6. As for the long-range monitoring, the significant negative nighttime amplitude decreases as propagation anomalies were found for two subionospheric paths: NWC (Australia)-PTK and JJY (Fukushima, Japan)-YSH during about a week, mainly before the first EQ. The anomalies of signal in the path JJY-PTK were observed 4 - 5 days before the second EQ and 3 days after it. Extensive analyses have been performed as well for these two EQs by using the short-range monitoring of VLF data observed at all of the seven VLF/LF stations in Japan in relation to the JJY signal. As related with the 1st EQ, there were observed anomalies on the two paths of JJY-STU (Suttsu) and JJY-NSB (Nakashibetsu) (both stations in Hokkaido) on 2 and 3 November. While, for the 2nd EQ clear anomalies have been observed on 14 and 15, and on 21 November at Ito station in Izu peninsula, Kamakura, Togane and Katsuura in Chiba. Taking into account the possible influence of other factors which can produce perturbations in VLF/LF signals and also using control paths, we may conclude that observed anomalies were very likely to be signatures of lower ionospheric perturbations caused by impending EQs. Finally, we try to estimate the possible perturbation scale for both EQs.展开更多
The amplitude scintillation detection is typically achieved by using the scintillation index generated by dedicated and costly ionospheric scintillation monitoring receivers(ISMRs).Considering the large volume of comm...The amplitude scintillation detection is typically achieved by using the scintillation index generated by dedicated and costly ionospheric scintillation monitoring receivers(ISMRs).Considering the large volume of common Global Navigation Satellite System(GNSS)receivers,this paper presents a strategy to accurately identify the ionospheric amplitude scintillation events utilizing the measurements collected with geodetic GNSS receivers.The proposed detection method relies on a pre-trained machine learning decision tree algorithm,leveraging the scintillation index computed from the carrier-to-noise data and elevation angles collected at 1-Hz.The experimental results using real data demonstrate a 99%accuracy in scintillation detection can be achieved.By combining advanced machine learning techniques with geodetic GNSS receivers,this approach is feasible to effectively detect ionospheric scintillation using non-scintillation GNSS receivers.展开更多
The spatial gradient induced by the Equatorial Plasma Bubble(EPB)in low latitude regions is a major challenge for the Ground Based Augmentation System(GBAS).To facilitate the implementation and operation of GBAS Appro...The spatial gradient induced by the Equatorial Plasma Bubble(EPB)in low latitude regions is a major challenge for the Ground Based Augmentation System(GBAS).To facilitate the implementation and operation of GBAS Approach Service Type(GAST)-D at Hong Kong International Airport,the impact of EPB induced spatial gradients needs to be analyzed.Previous simulations using a two-dimensional trapezoid model neglected the three-dimen-sional structure of the EPB,assuming ionospheric delay on a thin shell at a specific altitude.To address this limitation,this paper adopts a cube above the magnetic equator to characterize the EPB threat model.The ionospheric delay difference between satellite signals passing through the EPB model is limited by the upper bound spatial gradi-ent derived with the data collected from Hong Kong Satellite Positioning Reference Station Network.The simula-tion results reveal that ionospheric monitors in GAST D can satisfy the Category Il/ll approach requirement,i.e.,the probability of missed detection PMp for the diferential range error E,larger than 2.75 m is lower than1×10^(-9).The potentially hazardous event with the largest E,of 2.47 m and PmD of1.86×10^(-9) occurs when the satelite signal moves parallel to the equator near the Equatorial lonization Anomaly(ElA)region,and its significant portion traverses in the EPBdepletion region.展开更多
基金the Global GNSS-TEC data processing has been supported by JSPS KAKENHI Grant Number 16H06286。
文摘This study analyzes total electron content(TEC)variations during two solar eclipse events that occurred on October 25,2022,and October 14,2023.The solar eclipse of October 25,2022,was a partial solar eclipse,while the eclipse of October 14,2023,was an annular solar eclipse.For this study,the data of eight International GNSS Service(IGS)stations from different eclipse coverage zones are used to analyze TEC variations.It is found that the stations located in the maximum eclipse cover zone exhibited notable decreases in TEC values.The minimum variation of about 11.76%in TEC values is observed at the station situating in about 20 percent eclipse cover zone,while it varies from 22%to 38%at the stations falling in about 60 percent eclipse cover zone.The highest variation in TEC values of about 44%is found at the stations in about 80 percent eclipse cover zone.The time of occurrence of maximum depletion in TEC values at each station is in line with their longitudinal sequence.Atmospheric gravity waves(AGWs)are also observed by performing wavelet analysis on TEC data.The global TEC maps visualize and confirm observed TEC variations,providing spatial and temporal insights into the ionospheric response.This analysis highlights the influence of station location and eclipse coverage on the magnitude and spatial distribution of TEC variations.
文摘This paper demonstrates that the spatial distribution of the ionospheric TEC over the Indian region can be reconstructed with appreciable accuracy using minimal numbers of empirical orthogonal functions as a basis.These basis functions were derived using the Singular Value Decomposition of a matrix composed of pragmatic vertical Total Electron Content(VTEC)values collected across varied ionospheric conditions and measured over the region of interest.The reconstruction was achieved by linearly combining the appropriately chosen significant bases with corresponding weight factors.The reconstruction accuracy of the algorithm was found to be better than 4 TECU(TECU=1016electrons/m2)for more than 99.9%of the time when tested over the complete year of 2016 with only eight basis vectors.The containment factor,defined here,indicates the goodness of the chosen bases in representing the arbitrary VTEC distributions and is found to remain typically high,aiding in improved algorithm performance.The performance,however,was found to be sensitive to the seasons and geomagnetic conditions.Deteriorated performance was observed when tested for the St.Patrick's Day storm data.The deterioration was attributed to the structural alteration of the ionospheric plasma density and the presence of atypical modes during the storm.The results ascertain the prospect of a faithful representation of the spatial distribution of the ionospheric VTEC using limited parametric variables,which may find utility in navigation,radar,and various other applications.
基金supported by TUBITAK 112E568,114E092,and 115E915 projectsTNPGN-Active RINEX data set is available to the IONOLAB group for the TUBITAK 109E055 project。
文摘In this study,the gradients of Total Electron Content(TEC)for a midlatitude region are estimated and grouped with respect to the distance between neighboring stations,time periods within a day,and satellite directions.Annual medians of these gradients for quiet days are computed as templates.The metric distances(L2N)and Symmetric Kullback-Leibler Distances(SKLD)are obtained between the templates and the daily gradient series.The grouped histograms are fitted to the prospective Probability Density Functions(PDF).The method is applied to the Slant Total Electron Content(STEC)estimates from the Turkish National Permanent GPS Network(TNPGN-Active)for 2015.The highest gradients are observed in the east-west axis with a maximum of 25 mm/km during a geomagnetic storm.The maximum differences from the gradient templates occur for neighboring stations within100-130 km distance away from each other,during night hours,and for regions bordering the Black Sea and the Mediterranean in the northeast and southeast of Turkey.The empirical PDFs of the stationpair gradients are predominantly Weibull-distributed.The mean values of Weibull PDFs in all station groups are between 1.2 and 1.8 mm/km,with an increase during noon and afternoon hours.The standard deviations of the gradient PDFs generally increase during night hours.The algorithm will form a basis for quantifying the stochastic variations of the spatial rate of change of TEC trends in midlatitude regions,thus supplementing reliable and accurate regional monitoring of ionospheric variability.
文摘The measurements of very low frequency/low frequency (VLF/LF) signals at the Petropavlovsk-Kamchatsky (PTK) and Yuzhno-Sakhalinsk (YSH) stations in Russia and several observing stations in Japan were used for the analysis of lower ionospheric perturbations in possible association with two earthquakes (EQs) which occurred offshore the Pacific Ocean of Japan in November 2016. The first EQ with M (magnitude) = 6.1 (depth 42 km) happened close to the coast line on 11 November (UT). The second EQ was recorded in the sea on 21 November (UT) with M = 6.9 (depth 11 km) and they had a series of aftershocks with M up to 5.6. As for the long-range monitoring, the significant negative nighttime amplitude decreases as propagation anomalies were found for two subionospheric paths: NWC (Australia)-PTK and JJY (Fukushima, Japan)-YSH during about a week, mainly before the first EQ. The anomalies of signal in the path JJY-PTK were observed 4 - 5 days before the second EQ and 3 days after it. Extensive analyses have been performed as well for these two EQs by using the short-range monitoring of VLF data observed at all of the seven VLF/LF stations in Japan in relation to the JJY signal. As related with the 1st EQ, there were observed anomalies on the two paths of JJY-STU (Suttsu) and JJY-NSB (Nakashibetsu) (both stations in Hokkaido) on 2 and 3 November. While, for the 2nd EQ clear anomalies have been observed on 14 and 15, and on 21 November at Ito station in Izu peninsula, Kamakura, Togane and Katsuura in Chiba. Taking into account the possible influence of other factors which can produce perturbations in VLF/LF signals and also using control paths, we may conclude that observed anomalies were very likely to be signatures of lower ionospheric perturbations caused by impending EQs. Finally, we try to estimate the possible perturbation scale for both EQs.
基金supported by grants from the Research Grants Council of the Hong Kong Special Administrative Region,China (Project No.25202520,15214523)the National Natural Science Foundation of China (Grant No.42004029).
文摘The amplitude scintillation detection is typically achieved by using the scintillation index generated by dedicated and costly ionospheric scintillation monitoring receivers(ISMRs).Considering the large volume of common Global Navigation Satellite System(GNSS)receivers,this paper presents a strategy to accurately identify the ionospheric amplitude scintillation events utilizing the measurements collected with geodetic GNSS receivers.The proposed detection method relies on a pre-trained machine learning decision tree algorithm,leveraging the scintillation index computed from the carrier-to-noise data and elevation angles collected at 1-Hz.The experimental results using real data demonstrate a 99%accuracy in scintillation detection can be achieved.By combining advanced machine learning techniques with geodetic GNSS receivers,this approach is feasible to effectively detect ionospheric scintillation using non-scintillation GNSS receivers.
基金supported by grants from the Research Grants Council of the Hong Kong Special Administrative Region,China (Project No.25202520,15214523)the National Natural Science Foundation of China (Grant No.42004029)。
文摘The spatial gradient induced by the Equatorial Plasma Bubble(EPB)in low latitude regions is a major challenge for the Ground Based Augmentation System(GBAS).To facilitate the implementation and operation of GBAS Approach Service Type(GAST)-D at Hong Kong International Airport,the impact of EPB induced spatial gradients needs to be analyzed.Previous simulations using a two-dimensional trapezoid model neglected the three-dimen-sional structure of the EPB,assuming ionospheric delay on a thin shell at a specific altitude.To address this limitation,this paper adopts a cube above the magnetic equator to characterize the EPB threat model.The ionospheric delay difference between satellite signals passing through the EPB model is limited by the upper bound spatial gradi-ent derived with the data collected from Hong Kong Satellite Positioning Reference Station Network.The simula-tion results reveal that ionospheric monitors in GAST D can satisfy the Category Il/ll approach requirement,i.e.,the probability of missed detection PMp for the diferential range error E,larger than 2.75 m is lower than1×10^(-9).The potentially hazardous event with the largest E,of 2.47 m and PmD of1.86×10^(-9) occurs when the satelite signal moves parallel to the equator near the Equatorial lonization Anomaly(ElA)region,and its significant portion traverses in the EPBdepletion region.
