An innovative methodology for locating ionosphere layer height: case study on 2011 Tohoku-Oki earthquake and tsunami

<p>One of the main issues in GNSS ionosphere seismology is to localize the exact height of the single thin layer (H<sub>ion</sub>) with which the ionosphere is approximated. H<sub>ion</sub> is generally assumed to be the altitude of the maximum ionospheric ionization (hmF2), i.e., in the ionospheric F-layer. In this sense, H<sub>ion</sub> is often  be presumed from physical principles or ionospheric models. The determination of  H<sub>ion </sub>is, therefore, fundamental since it affects the coordinates of the ionospheric pierce point (IPP) and subsequentely of the sub-ionospheric pierce point (SIP).</p><p>In this work, we present a new developed methodology to determine the exact localization of H<sub>ion.</sub> We tested this approach on the TIDs (Travelling ionospheric disturbances) connected with the 2011 Tohoku-Oki earthquake and tsunami [1]. In detail, we computed the slant Total Electron Content (sTEC) variations at different H<sub>ion </sub>(in the range from 100 to 600 km) with the VARION (Variometric Approach for Real-Time Ionosphere Observation) algorithm [2,3], then we interpolated the different pattern in sTEC values related to different waves detected in the ionosphere (AGW<sub>epi</sub>, IGW<sub>tsuna</sub> and AW<sub>Rayleigh</sub>) finding the mean velocity value of these waves. Subsequentely, the minimized difference between the estimated propagation velocity and the values from physical models fix us the correct H<sub>ion.</sub></p><p>Our results show a H<sub>ion </sub>of 370 km, while ionopshere model IRI 2006 located the maximum of ionospheric ionization at an height of 270 km. This difference is important to understand how a different H<sub>ion</sub> can impact on the location of the sTEC perturbation, affecting the shape and the extent of the source from TEC observations.</p><p> </p><p> </p><p> </p><p> </p><p><strong>References</strong></p><p>[1] https://earthquake.usgs.gov/earthquakes/eventpage/official20110311054624120_30/executive</p><p>[2] Giorgio Savastano, Attila Komjathy, Olga Verkhoglyadova, Augusto Mazzoni, Mattia Crespi, Yong Wei, and Anthony J Mannucci, “Real-time detection of tsunami ionospheric disturbances with a stand-alone gnss receiver: A preliminary feasibility demonstration, ”Scientific reports, vol. 7, pp. 46607, 2017.</p><p>[3] Giorgio Savastano, Attila Komjathy, Esayas Shume, Panagiotis Vergados, Michela Ravanelli, Olga Verkhoglyadova, Xing Meng, and Mattia Crespi, “Advantages of geostationary satellites for ionospheric anomaly studies: Ionospheric plasma depletion following a rocket launch,”Remote Sensing, vol. 11, no. 14, pp. 1734, 2019</p>

EFEK GELOMBANG TSUNAMI ACEH 2004 PADA GANGGUAN IONOSFER BERGERAK SKALA MENENGAH DARI PENGAMATAN JARINGAN GPS SUMATRA

Medium Scale Travelling Ionospheric Disturbance (MSTID), thought to be manifestation of atmospheric gravity wave (AGW) in the ionospheric altitude that propagates horizontally and effects on in the electron density structure of ionosphere. These atmospheric gravity waves sourced from lower atmospheric activities such as typhoons, volcanic eruptions and tsunamis. Wave energy by its coupling induction process can travel to the ionosphere region. It has been understood that the TID's wave structure have an impact on the propagation of radio waves in the ionosphere so that it will affect the performance of navigation satellite-based positioning measurements. Based on Aceh tsunami in December 2004, this study aimed to investigation of the induction of atmospheric gravity waves in the ionosphere using total electron content (TEC) data from the Sumatra GPS network (Sumatra GPS Array, SUGAR). The detection technique of TEC changes due to AGW induction with a filter to separate medium scale disturbance at the ionospheric pierce point at an altitude of 350 km (IPP, Ionospheric Pierce Point). The results show the horizontal wavelength of a medium-scale TID around 180 ± 12 Km with a velocities of around 376 ± 9 ms-1. Based on two-dimensional map, the TID moves to the southeast.

Real-Time Positioning Accuracy Analysis of Single-Frequency GPS Based on Ionosphere Grid Products

Firstly, this paper introduces the common methods and accounts for the advantage of ionosphere grid products for correcting ionosphere errors with single-frequency GPS, according the analysis that ionosphere grid product can effectively ameliorate errors of single-frequency GPS navigation and positioning. In detail, this article gives the establishment, forecast and operation methods of ionosphere grid products, and introduces the method that calculates the VTEC (Vertical Total Electronic Contents) values of the geocentric latitude of the ionospheric pierce point, the VTEC values of four-point interpolation models and the single-layer mapping function. It’s also compares different pairs of ionosphere correction data and satellite ephemeris which use to analyze the impact of real-time positioning accuracy of single-frequency GPS. The experiments prove that the predicted ionosphere grid products can obviously improve the precision for single-frequency users, and have some practical values for single-frequency positioning and orbit determination.

Redes neurais artificiais aplicadas na previsão do VTEC no Brasil

Uma forma de se prever o conteúdo total de elétrons na direção vertical (VTEC - Vertical Total Electron Content) usando a arquitetura de redes neurais artificiais (RNA) denominada de perceptrons de múltiplas camadas (MLP - MultipLayer Percetrons) é apresentada e avaliada nesta pesquisa. As entradas do modelo foram definidas como sendo a posição dos pontos ionosféricos (IPP - Ionospheric Pierce Point) e o tempo universal (TU), enquanto que a saída é o VTEC. As variações sazonais e de períodos mais longos são levadas em conta através da atualização do treinamento diariamente. Testes foram conduzidos sobre uma área que abrange o Brasil e sua vizinhança considerando períodos de alta e baixa atividade solar. As RNA foram treinadas utilizando informações dos mapas globais da ionosfera (GIM - Global Ionospheric Maps) produzidos pelo serviço internacional do GNSS (IGS - International GNSS Service) das 72 horas anteriores à época de início da previsão. As RNA treinadas foram utilizadas para prever o VTEC por 72 horas (VTEC RNA). Os VTEC RNA foram comparados com os VTEC contidos nos GIM (VTEC GIM). A raiz do erro médio quadrático (RMS) da diferença entre o VTEC GIM e o VTEC RNA variou de 1,4 a 10,7 unidades de TEC (TECU). O erro relativo mostra que a RNA proposta foi capaz de prever o VTEC com 70 a 85% de acerto.

Path Optimization in Hull Part Cutting Based on Seven Bridges Problems

Generally the process of hull part cutting is that the part can not be cut until the previous part has been cut. This mode is poor cutting efficiency and high cutting cost. Based on the famous Seven Bridges Problems, this paper models the cutting problem and then presents a brand-new cutting technology, the bridge cutting. In this technology, only one pierce point is enough to cut off all the parts that lie in the same level. The example shows that the technology is effective for reducing the numbers of pierce points and shortening the length of idle cutting path, which not only improves the cutting efficiency but also saves the cutting cost.

On the validity of the ionospheric pierce point (IPP) altitude of 350 km in the Indian equatorial and low-latitude sector

The GPS data provides an effective way to estimate the total electron content (TEC) from the differential time delay of L1 and L2 transmissions from the GPS. The spacing of the constellation of GPS satellites in orbits are such that a minimum of four GPS satellites are observed at any given point in time from any location on the ground. Since these satellites are in different parts of the sky and the electron content in the ionosphere varies both spatially and temporally, the ionospheric pierce point (IPP) altitude or the assumed altitude of the centroid of mass of the ionosphere plays an important role in converting the vertical TEC from the measured slant TEC and vice versa. In this paper efforts are made to examine the validity of the IPP altitude of 350 km in the Indian zone comprising of the ever-changing and dynamic ionosphere from the equator to the ionization anomaly crest region and beyond, using the simultaneous ionosonde data from four different locations in India. From this data it is found that the peak electron density height (hpF2) varies from about 275 to 575 km at the equatorial region, and varies marginally from 300 to 350 km at and beyond the anomaly crest regions. Determination of the effective altitude of the IPP employing the inverse method suggested by Birch et al. (2002) did not yield any consistent altitude in particular for low elevation angles, but varied from a few hundred to one thousand kilometers and beyond in the Indian region. However, the vertical TEC computed from the measured GPS slant TEC for different IPP altitudes ranging from 250 to 750 km in the Indian region has revealed that the TEC does not change significantly with the IPP altitude, as long as the elevation angle of the satellite is greater than 50 degrees. However, in the case of satellites with lower elevation angles (<50°), there is a significant departure in the TEC computed using different IPP altitudes from both methods. Therefore, the IPP altitude of 350 km may be taken as valid even in the Indian sector but only in the cases of satellite passes with elevation angles greater than 50°.