GPS Ionospheric Scintillation And TEC Monitor Research Articles

Characterization of Ionospheric Delay and Forecasting Using GPS-TEC over Equatorial Region, Malaysia

This paper investigates the characteristic of the ionospheric delay and forecasting using modified statistical Holt-Winter method over Malaysia. This was carried out by using dual frequency GPS Ionospheric Scintillation and TEC Monitor (GISTM) receivers installed at the National University of Malaysia (UKM) (geographic coordinates 2.55°N, 101.46°E and geomagnetic coordinates 7.10°S, 174.05°E), and Langkawi national observatory (Langkawi) (geographical coordinates 6.19°N, 99.51°E and geomagnetic coordinates 3.39°S, 172.42°E), during 2011. In this work, the Holt-Winter forecasting method is modified to provide a better forecasting result over Malaysia. The diurnal, monthly, and seasonal variations of actual ionospheric delay have been analyzed and compared with forecasted ionospheric delay. Based on the results, the diurnal variability of ionospheric delay was maximal mostly between 12:00– 17:00 LT, and minimal nearly at 05:00 LT. The maximum monthly ionospheric delays occurred in October, which is attributed to the geomagnetic storm disturbance that caused increase in ionospheric delay. The lowest seasonal ionospheric delay occurred in the summer and the highest was during the equinox. The maximum ionospheric delay on a quiet day was around 41.9 TECU, while it reached up to 86.6 TECU during the geomagnetic storm. The Holt-Winter method exhibited the highest difference between the measurements and the forecasts in March, with an error of 6%. Hence, the modified Holt-Winter method forecast ionospheric delay effectively during quiet and disturbed periods over Malaysia.

PERBANDINGAN KARAKTERISTIK AKTIVITAS SINTILASI IONOSFER DI ATAS MANADO, PONTIANAK DAN BANDUNG DARI DATA PENERIMA GPS (CHARACTERISTICS COMPARISON OF IONOSPHERIC SCINTILLATION ACTIVITIES OVER MANADO, PONTIANAK AND BANDUNG BASED ON GPS RECEIVER DATA)

Ionospheric scintillation activity on certain region need to be known its characteristics since its occurrence can degrade satellite signal quality of global satellite navigation system (GNSS) and also satellite communication that works at L-band frequency. The occurrence of ionospheric scintillation varies with location. Therefore, this paper aimed to determine comparative charasteristics of ionospheric scintillation activity over Manado, Pontianak and Bandung from amplitude scintillation index S4 data derived from GPS receiver. The data obtained from the GPS Ionospheric Scintillation and TEC Monitor (GISTM) at Manado station (1.48o N; 124.85oE geomagnetic latitude 7.7oS), at Pontianak station (0.03o S;109.33oE geomagnetic latitude 9.7oS) and at Bandung (-6.90oS;107.6oE geomagnetic latitude 16.54oS) on July 2014 to June 2015. The data were classified into three categores : quiet, moderate and strong based on s4 index. Then we calculated percentage occurrence of scintillation monthly from each observation stastions and mapping of S4 index over Manado, Pontianak and Bandung. The results show that the presentage of strong scintillation (S4>0.5) above Manado is always lower than the other stastions. Strong scintillation was detected at one stations may not also detected at other stations. For very strong scintillastion event, the occurrence of strong scintillation could be detected by all observation stastions but vary in duration. Duration of strong scintillation over Bandung was the longest (up to 4 hours) compared to Pontianak (less than 2 hours) and Manado (less than 1 hour). Based on map of distribution scintillastion occurrence, strong scintillation occurs more intensively over Bandung than over Pontianak and Manado.

Study of GPS Position Error during 16 June, 2005 (Disturb Day) at Bhopal

In order to study GPS position error, the GPS Ionospheric Scintillation and TEC Monitor (GISTM) based GPS receiver was installed at an equatorial station, Bhopal (23.2° N, 77.4° E, Geomagnetic latitude 14.23˚ N), India. We analyzed the horizontal error and the level of confidence in terms of DRMS and CEP and positional error from fixed GPS point for 16 June 2005(disturb day). In order to study the effect of storm on GPS position errors, the latitudinal error and longitudinal error in meter is studied. We observed that the maximum number of error points in the latitudinal error lies between 1.95 to -1.57 meter while longitudinal error points lies between 1.09 to – 1.28 meter. It was observed that some of the error points lie out the 95% error ellipse and it is observed that the error point’s increased in N and N-E direction. The results have been compared with the earlier ones and discussed in terms of possible source mechanism responsible for the position error at anomaly crest region.

Comparison of GPS TEC variations with Holt-Winter method and IRI-2012 over Langkawi, Malaysia

The Total Electron Content (TEC) is the ionospheric parameter that has the main effect on radio wave propagation. Therefore, it is crucial to evaluate the performance of the TEC models for the further improvement of the ionospheric modelling in equatorial regions. This work presents an analysis of the TEC, derived from the GPS Ionospheric Scintillation and TEC Monitor (GISTM) receiver at the Langkawi station, Malaysia, located at the geographic coordinates of 6.19°N, 99.51°E and the geomagnetic coordinates of 3.39°S, 172.42°E. The diurnal, monthly and seasonal variations in 2014 of the observed GPS–TEC were compared with the statistical Holt-Winter method and a recent version of the International Reference Ionosphere model (IRI-2012), using three different topside options of an electron density, which are the IRI-2001, IRI01-corr and NeQuick. The maximum peaks of the GPS–TEC were observed in the post-noon time and the minimum was observed during the early morning time. In addition, in monthly variations the Holt-Winter and the IRI-2012 topside options showed an underestimation that was in agreement with the GPS–TEC, except for the IRI-2001 model which showed an overestimation in June, July and August. Regarding the seasonal variation of the GPS–TEC, the lowest values were observed during summer and it reached its maximum value during the equinox season. The IRI-2001 showed the highest value of percentage deviation compared to the IRI01-corr, NeQuick and Holt-Winter method. Therefore, the accuracy of the models was found to be approximately 95% in the Holt-Winter method, 75% in the IRI01-corr, 73% in the NeQuick and 66% in the IRI-2001 model. Hence, it can be inferred that the Holt-Winter method showed a higher performance and better estimates of the TEC compared to the IRI01-corr and NeQuick, while the IRI-2001 showed a poor predictive performance in the equatorial region over Malaysia.

PREDICTION OF TOTAL ELECTRON CONTENT OF THE IONOSPHERE USING NEURAL NETWORK

This paper presents the prediction of hourly Vertical Total Electron Content (VTEC) using a neural network by utilizing the data from a GPS Ionospheric Scintillation and TEC Monitor (GISTM) receiver for six years (from 2005 to 2010) during low to medium solar activity (Sunspot number (SSN) between 0.0 and 42.6). Several network configurations were investigated to observe the effect of the number of neurons, and hidden layers. Overall testing process for several network set-up yielded Root Mean Square Error (RMSE) value of 3 to 7 TECU, absolute error of 2 to 6 TECU and relative error of 8% to 28%. Testing using April 2010 to November 2010 data (SSN from 8.0 to 25.2) produced RMSE value of 2.95 to 3.88 TECU,absolute error of 2.39 to 3.09 TECU and relative error of 8.11% to 16.18%, which are within the acceptable range.

GNSS station characterisation for ionospheric scintillation applications

Ionospheric scintillations are fluctuations in the phase and amplitude of the signals from GNSS (Global Navigation Satellite Systems) occurring when they cross regions of electron density irregularities in the ionosphere. Such disturbances can cause serious degradation of several aspects of GNSS system performance, including integrity, accuracy and availability. The two indices adopted worldwide to characterise ionospheric scintillations are: the amplitude scintillation index, S4, which is the standard deviation of the received power normalised by its mean value, and the phase scintillation index, σΦ, which is the standard deviation of the de-trended carrier phase. Collaborative work between NGI and INGV supports a permanent network of GISTM (GPS Ionospheric Scintillation and TEC Monitor) receivers that covers a wide range of latitudes in the northern European sector. Data from this network has contributed significantly to several papers during the past few years (see e.g. De Franceschi et al., 2008; Aquino et al., 2009; Spogli et al., 2009, 2010; Alfonsi et al., 2011). In these investigations multipath effects and noise that contaminate the scintillation measurements are largely filtered by applying an elevation angle threshold. A deeper analysis of the data quality and the development of a more complex filtering technique can improve the results obtained so far. The structures in the environment of each receiver in the network which contaminate scintillation measurements should be identified in order to improve the quality of the scintillation and TEC data by removing error sources due to the local environment. The analysis in this paper considers a data set characterised by quiet ionospheric conditions of the mid-latitude station located in Nottingham (UK), followed by a case study of the severe geomagnetic storm, which occurred in late 2003, known generally as the “Halloween Storm”.

Single Parameter-Based Neural Networks Prediction of TEC

Total electron content (TEC) is a highly non-linear ionospheric parameter that is strongly affected by changes in the solar activity. Reliability of space-based systems is affected by TEC and hence requires the development of a good model to nowcast and forecast its variability. Therefore, the aim of this paper is to present a Neural Networks (NN) model to predict the TEC variability. Slant TEC (sTEC) from the GPS Ionospheric Scintillation and TEC Monitor (GISTM) receiver is calculated and converted to vertical TEC (vTEC) based on the Single Layer Model (SLM). As a preliminary study, only one variable is considered as an input parameter for the NN, which is the hourly vTEC values and this is used to train the network with feed forward back propagation (BP) algorithm. The data set is the observed TEC for April and May 2005. Absolute maximum error and root mean square error (RMSE) are then calculated for each trained NN to evaluate the performance of the model. Analysis of the results reveals that, on average, the NN model is capable to predict TEC values but however extended input data set is needed to improve the generalization capability and reliability of the model. The highest absolute maximum error is 17 TECU and the smallest absolute maximum error is 6 TECU. The RMSE values for May 27 to May 30 are 1 TECU, 4 TECU, 5 TECU and 1 TECU, respectively.

Investigation of ionospheric scintillation at UKM station, Malaysia during low solar activity

In this paper the investigation of the occurrence of ionospheric scintillation with S4≥0.2 was conducted by using a dual-frequency GISTM (GPS Ionospheric Scintillation and TEC monitor) at Universiti Kebangsaan Malaysia station, Malaysia (2.55°N, 101.46°E; geomagnetic: 7.39°S, 173.63°E) between September 2009 and December 2010. The study shows that significant nighttime amplitude scintillation event with 0.4≤S4<0.6 mainly occurred in the months of March, September and October, while significant daytime amplitude scintillation activity took place in November and December with 0.3≤S4<0.5. Moreover, nighttime amplitude scintillation observed at UKM station always occurred with phase scintillations, total electron content (TEC) depletions, rate of change of TEC (ROT) fluctuations and the enhancement of rate of TEC index (ROTI). Nevertheless, during daytime amplitude scintillation, TEC depletions and ROT fluctuations were much weaker than those that occurred during nighttime and this may be caused by small scale irregularities in the E region, called sporadic-E (Es), while the occurrences of nighttime amplitude scintillation maybe caused by the ionospheric irregularities in the F region.

Nighttime enhancements in TEC near the crest of northern equatorial ionization anomaly during low solar activity period

Enhancement in nighttime total electron content (TEC) near the crest of equatorial ionization anomaly at Bhopal (Geog. 23.2°N, 77.4°E, and MLAT 14.2°N) has been studied for the solar minimum period March 2005- November 2006. TEC data recorded by GPS Ionospheric Scintillation and TEC Monitor (GISTM) GSV4004A receiver is used for the study and results are presented in the paper. More than 10% increase in TEC with respect to background content is considered for analysis. Out of total 138 enhancements, 65 observed during pre midnight hours and 73 during post midnight hours. It is observed that nighttime enhancement in TEC at Bhopal occurs in all seasons; it is more frequent during summer, less during equinox and least during winter months. The enhancement in nighttime TEC can be observed both in geomagnetic disturbed time and in quiet time. We found that mean peak amplitude for pre-midnight TEC enhancement are more in equinox and less in winter, while in post-midnight TEC enhancement it is highest in summer and less in winter. Post-midnight enhancements have smaller peak amplitude as compared to pre-midnight. Also the most probable values for pre- and post-midnights are 4.4 TECU and 2.17 TECU respectively. The percentage occurrence of nighttime TEC enhancement does not show any dependence on solar activity whereas the peak amplitude depends on solar activity. The percentage occurrence of nighttime TEC enhancement decreases as the magnetic activity increases whereas there is no such dependency found with peak amplitude. It is also observed that majority of nighttime TEC enhancements are occurred without scintillation. The localised nighttime TEC enhancements near the crest of equatorial ionization anomaly region have been observed most of the nights during the period of study.

GPS scintillation and TEC gradients at equatorial latitudes in April 2006

We use observations of ionospheric scintillation at equatorial latitudes from two GPS receivers specially modified for recording, at a sampling rate of 50 Hz, the phase and the amplitude of the L1 signal and the Total Electron Content (TEC) from L1 and L2. The receivers, called GISTM (GPS Ionospheric Scintillation and TEC Monitor), are located in Vietnam (Hue, 16.4°N, 107.6°E; Hoc Mon, 10.9°N, 106.6°E). These experimental observations are analysed together with the tomographic reconstruction of the ionosphere produced by the Multi-Instrument Data Analysis System (MIDAS) for investigating the moderate geomagnetic storm which occurred on early April 2006, under low solar activity. The synergic adoption of the ionospheric imaging and of the GISTM measurements supports the identification of the scale-sizes of the ionospheric irregularities causing scintillations and helps the interpretation of the physical mechanisms generating or inhibiting the appearance of the equatorial F layer irregularities. In particular, our study attributes to the turning of the IMF (Interplanetary Magnetic Field) between northward and southward direction an important role in the inhibition of the generation of spread F irregularities resulting in a lack of scintillation enhancement in the post-sunset hours.

Climatology of GPS ionospheric scintillations over high and mid-latitude European regions

Abstract. We analyze data of ionospheric scintillation in the geographic latitudinal range 44°–88° N during the period of October, November and December 2003 as a first step to develop a "scintillation climatology" over Northern Europe. The behavior of the scintillation occurrence as a function of the magnetic local time and of the corrected magnetic latitude is investigated to characterize the external conditions leading to scintillation scenarios. The results shown herein, obtained merging observations from four GISTM (GPS Ionospheric Scintillation and TEC Monitor), highlight also the possibility to investigate the dynamics of irregularities causing scintillation by combining the information coming from a wide range of latitudes. Our findings associate the occurrences of the ionospheric irregularities with the expected position of the auroral oval and ionospheric troughs and show similarities with the distribution in magnetic local time of the polar cap patches. The results show also the effect of ionospheric disturbances on the phase and the amplitude of the GPS signals, evidencing the different contributions of the auroral and the cusp/cap ionosphere.