Search

The ionospheric effect plays a crucial role in the radio communications. For ionospheric observing and monitoring, the Global Navigation Satellite System (GNSS) has been widely utilized. The ionospheric condition can be characterized by the Total Electron Contents (TEC) and TEC Rate (TECR) calculated from the GNSS measurements. Currently, GNSS-based ionospheric observing and monitoring largely depend on a global fiducial network of GNSS receivers such as the International GNSS Service (IGS) network. We propose a new approach to observe the ionosphere by deploying a GNSS receiver on a Hong Kong Mass Transit Railway (MTR) train. We assessed the TECR derived from the MTR-based GNSS receiver by comparing it with the TECR derived from a static GNSS receiver. The results show that the Root-Mean-Squares (RMS) errors of the TECR derived from the MTR-based GNSS receiver is consistently approximately 23% higher than that derived from the static GNSS receiver. Despite the increased error, the findings suggest that the GNSS observation on a fast-moving platform is a feasible approach to observe the ionosphere over a large region in a rapid and cost-effective way.

The single-frequency users of Global Navigation Satellite System (GNSS) require an effective mathematical model that mitigate the dominant errors due to ionospheric delays. Klobuchar model approximately reduces ionospheric effect up to 50% through its coefficients in the navigation message, which is not sufficient for the GNSS single frequency users at critical applications. Hence, a new model, for Single Frequency GNSS User Applications using Klobuchar model driven by Auto Regressive Moving Average Method (SAKARMA) is proposed to forecast and enhance the precision of ionospheric delay estimations for GNSS users. The hourly VTEC maps are obtained from the Assimilated Indian Regional Vertical Total Electron Content (AIRAVAT) by the process of data assimilation using the Kalman filter exclusively for the Indian region (longitude: 65°E to 100°E; latitude: 5°N to 40°N) using 26 GPS TEC stations over Indian region. The accuracy of the SAKARMA model is investigated using the AIRAVAT maps for various Indian geographic regions during both geomagnetic quiet and disturbed conditions of September month in 2016 year. Furthermore, in order to test SAKARMA model, a dual-frequency Navigation with Indian Constellation (NavIC) receiver located at the KL Education Foundation, Guntur, India (geographic: 16.37°N, 80.37°E; geomagnetic: 7.44°N, 153.75°E) is used to collect the observations during 2 - 12 September 2017. Furthermore, SAKARMA model is also validated with Klobuchar model, Klobuchar-style coefficients provided by the Center for Orbit Determination in Europe (CODE) (CODKlob) Model, BeiDou System (BDS2) Model and NeQuick 2 Model over a low latitude NavIC station in forecasting the ionospheric delays. The experimental results of SAKARMA for NavIC have revealed that the MAPE for proposed SAKARMA model is 9-17% (accuracy: 83-91%), while 34-53% (accuracy: 47-66%) for the Klobuchar model. Thus, the results illustrate that the proposed SAKARMA model is capable of predicting the ionospheric delays for single frequency GNSS/NavIC users.

NavIC is India's own regional satellite-based navigation system that operates in L5 and in the unique S-band of frequencies. Still now, NavIC single point positioning is done and NavIC PPP or RTK is not availabel. Therefore, to find out a method for obtaining the best possible solution quality using NavIC dual frequency operation, this paper studies the ionospheric delay in L5 and S bands and the associated dual-frequency position solution qualities from two locations in eastern India. It is seen that the ionospheric delay (ionodelay) values are least during early morning hours (3–6 am IST) and the ionodelay values are less in S-Band. The solution qualities are also found to be the best during that same time span as observed through repeated data for several days. Till the availability of NavIC PPP, differential NavIC or NavIC RTK, therefore, for obtaining the best possible precise location solution in NavIC standalone mode, data should be collected during 3–6 am IST.

In this work, we present a methodology for correcting the major dominating errors in SAR interferograms. Ionospheric effect, orbital and tropospheric errors can lead to a serious damage the interferometric phase, and case a limitation for the retrieval of land displacement information carried by the SAR phase. To reduce the effect of these errors on an interferogram, a combined correction is applied, the Split-Spectrum Algorithm (SSA) is used for the correction of Ionospheric effect, in addition, the GACOS data is employed for tropospheric error, and finally, to quantify orbital contribution, a nonlinear model is used. This methodology is applied to a set of Sentinel-1 data; the preliminary results show an improvement of the information after the application of this joint correction.

The current cycle slip detection methods of Global Navigation Satellite System (GNSS) were mostly proposed on the basis of assuming the ionospheric delay varying smoothly over time. However, these methods can be invalid during active ionospheric periods, e.g., high Kp index value and scintillations, due to the significant increase of the ionospheric delay. In order to detect cycle slips during high ionospheric activities successfully, this paper proposes a method based on two modified Hatch⁻Melbourne⁻Wübbena combinations. The measurement noise in the Hatch⁻Melbourne⁻Wübbena combination is minimized by employing the optimally selected combined signals, while the ionospheric delay is detrended using a smoothing technique. The difference between the time-differenced ambiguity of the combined signal and this estimated ionospheric trend is adopted as the detection value, which can be free from ionospheric effect and hold the high precision of the combined signal. Five threshold determination methods are proposed and compared to decide the cycle slip from the magnitude aspect. This proposed method is tested with triple-frequency Global Navigation Satellite System observations collected under high ionospheric activities. Results show that the proposed method can correctly detect and fix cycle slips under disturbed ionosphere.

On the background of seasonal and helio-geomagnetic disturbances, disturbances of the ionization density near noon connected to earthquakes are investigated. The study is performed for some tens of earthquakes with magnitudes M>5 and depths hR=exp(M)+150 km. The analysis is performed using data registered by the three sounding stations every hour during 30 years. Especially methods of the statistical analysis are applied to search for regularities in the lithospheric-ionospheric links before and after earthquakes. The growth of the mean ionization density N at the F-layer electron density maximum Fof2 five-three days before earthquakes, and the decrease of N approaching the eruption and during a few days after the earthquake is investigated in dependence on both the magnitude of the earthquake M and the ionization density N near the F-layer maximum. It is found that some days before earthquakes the decrease of the ionization density ΔN is proportional to the values of M and N. After the earthquakes, ΔN depends much weaker on the magnitude M, and it is not influenced by the ionization density N. The variations of the ionization density three days before earthquakes do not depend on N and M (within the same order of approximation).

The paper objective is to demonstrate the possibility of studying irregular variations of the total electron content (TEC) of the ionosphere using GPS data of single-frequency measurements. This is considered by the example of registering the time behavior of the oblique TEC during the 20 March 2015 solar eclipse. As the initial data, we used single-frequency and dual-frequency phase and code measurements from the station MORP which is a part of the International IGS Network. As a result, by comparing the data of TEC time courses for two modes it is shown both qualitative agreement (TEC significant decrease during the eclipse) and quantitative agreement of results after appropriate treatment.

This paper shows the analysis results of time offsets using P1, P2 and P3 code in GPS time transfer. The r2cggtts program has been used in GNSS Time Transfer and use the P3 ionosphere free combination of P1 and P2 code measurements. We modified the r2cggtts program in order to calculate and write all kinds of time offsets P3 as well as P1 and P2. The result of the modified r2cggtts program shows that time offsets using P1 and P2 are of wide distribution comparing to time offsets using P3. In order to Figure out the error factors for wide distributions of P1 and P2, we analyze and present the relation between the elevation angle and time offsets in this paper.

The Terrain Observation by Progressive Scans (TOPS) acquisition mode of the Sentinel-1 mission provides a wide coverage per acquisition with resolutions of 5 m in range and 20 m in azimuth, which makes this acquisition mode attractive for glacier velocity monitoring. Here, we retrieve surface velocities from the southern Ellesmere Island ice caps (Canadian Arctic) using both offset tracking and Differential Interferometric Synthetic Aperture Radar (D-InSAR) techniques and combining ascending and descending passes. We optimise the offset tracking technique by omitting the azimuth offsets. By doing so, we are able to improve the final resolution of the velocity product, as Sentinel-1 shows a lower resolution in the azimuth direction. Simultaneously, we avoid the undesired ionospheric effect manifested in the data as azimuth streaks. The D-InSAR technique shows its merits when applied to slow-moving areas, while offset tracking is more suitable for fast-moving areas. This research shows that the methods used here are complementary and the use of both to determine glacier velocities is better than only using one or the other. We observe glacier surface velocities of up to 1200 m year − 1 for the fastest tidewater glaciers. The land-terminating glaciers show typical velocities between 12 and 33 m year − 1 , though with peaks up to 150 m year − 1 in narrowing zones of the confining valleys.

In the past few years, precise point positioning (PPP) has become an important positioning method for many practical applications. It is based on ionosphere-free carrier phase combination measurements, in which only first-order ionospheric error is removed. Past research has shown that high-order ionospheric effect can affect PPP performance. In this study, the effect of high-order ionospheric error, the second-order one, on PPP has been evaluated in Hong Kong, a low latitude area. First, a method regarding how to calculate second-order ionospheric error is introduced and the evaluation method is also discussed. After that, the numerical results are shown. Based on the results, it is found that the effect of the second-order ionospheric error on ionosphere-free carrier phase combination measurements reached up to the cm level in 2001 and the effect of the second-order ionospheric error on both kinematic and static PPP also reached the cm level. Further, it is also demonstrated that the effect of second-order ionospheric error on PPP is closely related to solar activity.

The data, obtained for the first time, permit the conclusion to be drawn, with a high degree of probability, that large meteors similar to the Chelyabinsk meteor, while entering the Earth’s atmosphere, are able to cause perturbations within the whole ionospheric stratum, rather than only at the sporadic Es layer altitudes, as previously thought.

In recent years, large number of Interferometric SAR applications in earthquake, cryosphere and tectonic geodesy show the great needs for ionospheric effect correction [1–4]. Several approaches, which mainly include the split spectrum InSAR technique, the Faraday rotation based method and the azimuth shift based method (the Multiple Aperture Interferometric and conventional azimuth shift) have been proposed to meet this end [5–11]. These techniques exploit different aspects — phase delay, polarimetric property and geometric distortion of the ionospheric effect on SAR data to retrieve the differential ionosphere in InSAR. These techniques work well in certain conditions, however, their performance might be limited in cases due to noise effect and the weakness of each technique itself. In this study, we are proposing a combined estimator by joining the Faraday rotation based method and the split spectrum technique of InSAR ionospheric effect correction, which is supposed to achieve a more robust and higher accuracy performance comparing to individual technique itself.

This paper presents the results of modeling the ionospheric effect of the seismogenic electrostatic field (SEF) seen at the earth’s surface as a perturbation of the vertical atmospheric electrostatic field in the earthquake preparation zone. The SEF distribution at ionospheric altitudes is obtained as an analytical solution of the continuity equation for the electric current density. It is shown that at night, the horizontally large scale SEF can efficiently penetrate into the ionosphere and produce noticeable changes in the horizontal distribution of the F region electron density. The results suggest that the seismogenic electrostatic field could be a possible source for the ionospheric variations observed over Taiwan before the strong Chi Chi earthquake of September 21, 1999.

Malaysia had in the past sent two remote sensing satellites to orbit by collaborating with foreign space companies to build homegrown capacities for space technology development. At the educational institutions, a pico-satellite development program would be an ideal first step to establish such capacity as students could gain the experience and know-how through the complete cycle of designing, building and testing a satellite. As it is now, some of their overseas counterparts have already succeeded in running CubeSat programs due to strong support from kit manufacturers and their national space agencies. However, the cost to purchase such kits could be discouraging and National Space Agency (ANGKASA) recognises the needs to initiate some designs that could be used or referred to for further development or expansion. In this paper, a hardware design of On-Board Data Handling (OBDH) board using PIC Microcontroller is presented. OBDH is a main subsystem which controls all subsystems in the satellite. It provides a series of important services like command, telemetry, data communication, data acquisition, process, storage and management. The PIC Microcontroller made by Microchip Corporation is chosen as it is widely used by the industry and academia in Malaysia. The 16-bit PIC24 microcontroller has been recognized as a suitable part due to its performance, memory, peripherals, cost effective solutions as well as availability. The method used in designing the OBDH in this pico-satellite is first based on a main mission to investigate ionospheric effect on GPS signal transmission. Other considerations taken are that the parts used should be of commercial off the shelf product and having its own development board for ease of testing. The expected result would be the successful arrangement of all required parts in limited pico-satellite’s size and the accomplishment in achieving the satellite’s missions through simulation.

The nadir ionospheric TEC is retrieved from TOPEX/POSEIDON (T/P) and JASON-1 along track altimetry database. After careful comparison, it is found that the nadir TEC and the zenith TEC from GIM, IRI is identical with each other in large scale, long term variation. Seasonal and 11 year periodical variations of the TEC difference between GIM and T/P can be identified. A difference about 1 to 2 TECU between T/P and Jason-1 TEC is noticed. Where, the IRI is not precise enough to calibrate the satellite altimetry data due to the poor spatial and time resolution. Around Japan Islands, the difference between GEONET TEC and Jason-1 shows both of the biases of Jason-1 and of the failed calibration if GEONET duel frequency GPS observables., 資料番号: AA0047899164

The electric field strength of three broadcasting stations - CLT (189 kHz, Sicily, Italy), MCO (216 kHz, France) and of CZE (270 kHz, Czech Republic) - has been monitored since 1997 with a sampling frequency of ten minutes at two sites, named AS and PE, located in the Central Apennines (Central Italy). The strongest seismic activity occurring in Central Italy during the last decade was the 1997–1998 Umbria-Marche seismic sequence; over a period of eight months, seven earthquakes with magnitudes greater than 5.0 occurred. The distances of the epicentres from the radio receivers were over 100 km. Unfortunately, at the PE site there were problems with both the power supply and saturation of the recorded signals so we could not use the data from this receiver in this study. At the AS measurement site, no anomalies were evident in the signals received from the three broadcasting stations before the main seismic event (M=5.9) of September 26, 1997. However, during February 1998, we observed a significant increase in the electric field strength of the CZE broadcasting station. On March 26, 1998 a strong earthquake (M=5.5) occurred in the same zone, starting the final phase of the Umbria-Marche seismic sequence. The seismic sequence was shallow with focal depths ranging from 1 km to a maximum of 10 km; on the contrary the March 1998 earthquake was unusual because of its great focal depth (∼ 50 km). The path from the CZE station to the receiver crosses the epicentral zone so it is possible that the increase in signal strength detected could be a precursor of the March 1998 earthquake, possibly related to an ionospheric effect. On the basis of a single observation, however, one can only tentatively suggest this as a precursor.

The ionosphere is the main error source in GNSS measurements and in extreme cases can degrade the positioning significantly, with errors exceeding 100 m; therefore, modelling and predicting of this type of error is crucial and critical. The ionospheric effect can be reduced using different techniques, such as dual-frequency receiver or suitable augmentation system (DGPS, SBAS); the aforesaid approaches involve the use of expensive devices and/or complex architectures. Single frequency stand-alone receivers are the cheapest and most widespread GNSS devices; they can estimate and partially correct the error due to the ionosphere, through adequate algorithms, which use parameters broadcasted by the navigation message. The aim of this paper is performance assessment of the ionospheric model NeQuick, adopted by the European GNSS Galileo for single frequency receivers. The analysis is performed in measurements domain and the data are collected in different geographical locations and in various geomagnetic conditions.

Ionospheric signal distortions are commonplace in low-frequency space-borne SAR observations and can lead to the degradation of SAR data quality and data consistency if no signal compensation is applied. In this paper we will give an overview of the problem of ionospheric influence in SAR, PolSAR, and InSAR data. We will characterize the spatio-temporal signal properties of ionospheric signals, introduce a selection of currently available correction methods, and present a list of performance requirements to be met by ionospheric correction.

Many GPS networks which were initially surveyed with Texas Instruments TI-4100 receivers have now been resurveyed with mixtures of TI-4100 and Trimble 4000 receivers or exclusively with Trimble receivers. In order to make confident tectonic interpretation of displacements observed between such surveys, it is necessary to understand any biases which may be introduced by using different receiver types or by mixing receivers within a network. Therefore, one of the primary objectives of the Ecuador 1990 GPS campaign (February 1990) was to provide a direct long baseline comparison between the TI-4100 and Trimble 4000SDT GPS receivers. p ]During this campaign, TI and Trimble receivers were co-located at each end of a 1323 kilometer baseline (Jerusalen to Baltra). Solutions for this baseline show no variation with receiver type. Zero-length baseline solutions showed no evidence for any intrinsic bias caused by mixing the two receiver types. Short baseline solutions indicate a bias of -34±10 mm in the baseline vertical component; the sign of the bias indicates that either the assumed phase center location for the TI is too low or the assumed location for the Trimble is too high. The bias is explainable if the phase centers of the Trimble SDT and SST antennas are similarly located. p ]Solutions for baselines measured with codeless receivers (such as the Trimble) should be as precise as those for baselines measured with P-code receivers (such as the TI) as long as it is possible to resolve ambiguities. Resolution of the widelane ambiguity is the limiting factor in ambiguity resolution with any codeless receiver, and in the February 1990 campaigns it was not successful fore baselines longer than 100 km. Without explicit modeling of the ionospheric effect on the widelane, ambiguity resolution with codeless receivers will not be successful for baselines longer than about 100 km, depending on the local ionospheric conditions.

An overview of the factors responsible in degradation of GPS (Global Positioning System) is described. Moreover, the major sources of error, their cause and how to reduce their effects are briefly discussed. Range errors such as ionospheric and tropospheric delays and equipment errors such as noise and multipath are separately explained. The latest developments in enhancing the quality of GPS technology are mentioned.

Global warning is now known to be the major environmental issue mankind will have to face in the next decade. Monitoring of vegetation and biomass is clearly an essential piece of information required at all levels ranging from the scientific studies to understand and forecast, to the political actors and government leaders responsible for drafting remediation policies and evaluating their impact. Microwave remote sensing with the low-frequency SAR technique can provide a useful characterization of forest (spatial coverage, species, density, height…) at a global scale, relying on the all-weather imaging capabilities of SAR linked with the significant penetration of the low-frequency EM wave in the canopy. The published techniques for forest characterization from low frequency SAR data include radiometry inversion, polarimetric inversion based on the anisotropy parameters and PolInSAR Random Volume Over Ground inversion. In this paper, we will more specifically concentrate on the PolSAR technique and the impact of ionospheric effect.

In this paper, we analyse the potential associated with a compact polarimetry (CP) P band spaceborne SAR system. Indeed, this architecture allows polarimetric acquisition without the usual reduction in swath. The CP data is shown to be almost equivalent to the full polarimetric data over extended targets, and the PolInSAR analysis can be performed without a significant loss of performance.