TEC

About: TEC is a research topic. Over the lifetime, 5119 publications have been published within this topic receiving 84696 citations.

Ionospheric studies for the implementation of GAGAN

Abstract: Satellite Based Augmentation System (SBAS), being developed by Indian Space Research Organization (ISRO) in collaboration with Airports Authority of India (AAI) is known as “GPS Aided GEO Augmented Navigation” (GAGAN). It is expected to offer better accuracy and integrity of navigation service than with GPS alone by providing correction terms to the GPS signals. This is achieved by modelling a Near Real Time Grid Based Ionospheric Delay Model for correcting propagation delay at 1575.42 MHz (L1) using measurements at 1575.42 and 1227.6 MHz (L2). Existing algorithms are replaced by Kriging based model to meet the requirement of correction with 0.5 m maximum residue over Indian region. Details of the data collection and pre-processing, including estimation of the Total Electron Content (TEC), which is a measure of ionospheric delay, has been described. Kriging algorithm and some preliminary results of studies are also presented in this paper. This includes the spatial decorrelation of the stochastic random field over the deterministic variation of ionospheric TEC. Its variation with time and locations are investigated and a temporal dependence found to exist. Large scale ionospheric irregularities and depletions that cause severe amplitude and phase scintillations are also studied. Their impacts on GAGAN are also shown. Some major scientific studies required to be carried out over Indian region to improve the GAGAN performance is discussed.

Spherical cap harmonic analysis of the Arctic ionospheric TEC for one solar cycle

Abstract: Precise knowledge of the Arctic ionosphere total electron content (TEC) and its variations has scientific relevance due to the unique characteristics of the polar ionosphere. Understanding the Arctic TEC is also important for precise positioning and navigation in the Arctic. This study utilized the spherical cap harmonic analysis (SCHA) method to map the Arctic TEC for the most recent solar cycle from 2000 to 2013 and analyzed the distributions and variations of the Arctic TEC at different temporal and spatial scales. Even with different ionosphere conditions during the solar cycle, the results showed that the existing International Global Navigation Satellite Systems Service stations are sufficient for mapping the Arctic TEC. The SCHA method provides adequate accuracy and resolution to analyze the spatiotemporal distributions and variations of the Arctic TEC under different ionosphere conditions and to track ionization patches in this polar region (e.g., the ionization event of 26 September 2011). The results derived from the SCHA model were compared to direct observations using the Super Dual Auroral Radar Network radar. The SCHA method is able to predict the TEC in the long and short terms. This paper presented a long-term prediction with a relative uncertainty of 75% for a latency of one solar cycle and a short-term prediction with errors of ±2.2 total electron content units (TECUs, 1 TECU = 1016 el m−2), ±3.8 TECU, and ±4.8 TECU for a latency of 1, 2, and 3 days, respectively. The SCHA is an effective method for mapping, predicting, and analyzing the Arctic TEC.

An Assessment of the Current WAAS Ionospheric Correction Algorithm in the South American Region

Abstract: The Federal Aviation Administration’s (FAA) Wide Area Augmentation System (WAAS) for civil aircraft navigation is focused primarily on the Conterminous United States (CONUS). The ionospheric correction algorithms for WAAS have been characterized extensively for this mid-latitude region of the ionosphere where benign conditions usually exist. Researchers are facing a more formidable challenge in addressing the ionospheric impact on navigation using Satellite-Based Augmentation Systems (SBAS) in other parts of the world such as the South American region. At equatorial latitudes, geophysical conditions lead to the so-called Appleton-Hartree (equatorial) anomaly phenomenon, which results in significantly larger ionospheric range delays and range delay spatial gradients than is observed in the CONUS region. In this paper, we use data from the South American region to perform a preliminary quantitative assessment of the performance of WAAS correction algorithms in this region. For this study, we accessed a world-wide network of 230 dual-frequency GPS receivers. The network includes: 1) the Continuously Operating Reference Sites (CORS) in the United States; 2) stations in and near South America as part of the Brazilian Network of Continuous Monitoring of GPS (RBMC), operated by the Brazilian Institute of Geography and Statistics (IGBE); and (3) sites included in the International GPS Service (IGS) global network. Data sets have been selected to include both a quiet and geomagnetically disturbed day. To provide ground-truth and calibrate GPS receiver and transmitter inter-frequency biases, we processed the GPS data using Global Ionospheric Mapping (GIM) software developed at the NASA Jet Propulsion Laboratory to compute calibrated high resolution observations of ionospheric total electron content (TEC). We assessed the WAAS’s planar fit algorithm in the equatorial region where the spatial gradients and the absolute slant TEC are known to be the highest in the world. We found that in Brazil the dominant error source for the WAAS planar fit algorithm is the inherent spatial variability of the equatorial ionosphere with ionospheric slant range delay residuals as high as 15 meters and root- mean square residuals for the quiet day of 1.9 meters. This compares to a maximum residual of 2 meters in CONUS, and 0.5 meter RMS. We revealed that ionospheric gradients in Brazil are at the 2 meter over 100 km level. Contrary to results obtained for CONUS, we discovered that a major ionospheric storm had a small impact on the planar fit residuals in Brazil.

On the responses to solar X-ray flare and coronal mass ejection in the ionospheres of Mars and Earth

Abstract: [1] We have used Mars Global Surveyor (MGS) observations for the period 12 to 18 May 2005 to address the effect of X-ray flare and Coronal Mass Ejection (CME) on the Total Electron Content (TEC) of the E region ionosphere of Mars during a violent solar event that occurred on 13 May. Modeling of E region TEC was also carried out for the time of the flare using the observed X-ray flux. We report that the solar flare caused enhancements in the TEC of Mars by factors of 6 to 10. A response was also observed in the E region plasma frequency of the Earth's ionosphere at nearly same time as the MGS observations. Our results suggest that sporadic E layer plasma frequency and TEC can increase by factors of 3 to 6 during the arrival of a CME at both Earth and Mars.