Solar activity dependence of total electron content derived from GPS observations over Mbarara

Vertical total electron content (VTEC) observed at Mbarara (geographic co-ordinates: 0.60°S, 30.74°E; geomagnetic coordinates: 10.22°S, 102.36°E), Uganda, for the period 2001–2009 have been used to study the diurnal, seasonal and solar activity variations. The daily values of the 10.7 cm radio flux (F_10.7) and sunspot number (R) were used to represent Solar Extreme Ultraviolet Variability (EUV). VTEC is generally higher during high solar activity period for all the seasons and increases from 0600 h LT and reaches its maximum value within 1400 h–1500 h LT. All analysed linear and quadratic fits demonstrate positive VTEC-F_10.7 and positive VTEC-R correlation, with all fits at 0000 h and 1400 h LT being significant with a confidence level of 95% when both linear and quadratic models are used. All the fits at 0600 h LT are insignificant with a confidence level of 95%. Generally, over Mbarara, quadratic fit shows that VTEC saturates during all seasons for F_10.7 more than 200 units and R more than 150 units. The result of this study can be used to improve the International Reference Ionosphere (IRI) prediction of TEC around the equatorial region of the African sector.     

Response of the EIA ionosphere to the 7-8 May 2005 geomagnetic storm

In this paper, response of low latitude ionosphere to a moderate geomagnetic storm of 7–8 May 2005 (SSC: 1920 UT on 7 May with Sym-H minimum, ∼−112 nT around 1600 UT on 8 May) has been investigated using the GPS measurements from a near EIA crest region, Rajkot (Geog. 22.29°N, 70.74°E, Geomag.14°), India. We found a decrease in total electron content (TEC) in 12 h after the onset of the storm, an increase during and after 6 h of Sym-H deep minimum with a decrease below its usual-day level on the second day during the recovery phase of the storm. On 8 May, an increase of TEC is observed after sunset and during post-midnight hours (maximum up to 170%) with the formation of ionospheric plasma bubbles followed by a nearly simultaneous onset of scintillations at L-band frequencies following the time of rapid decrease in Sym-H index (−30 nT/h around 1300 UT).     

Near-real time monitoring of the TEC fluctuations over the northern hemisphere using GNSS permanent networks

Since the early 1990s, global positioning system measurements have been used to study of the state and rapid changes of the Total Electron Content in the ionosphere. Currently, the increasing number of permanent stations makes it possible to generate maps of the irregularities in the ionosphere for specified regions with sub-daily resolution. The main goal of this work was to apply global navigation satellite system observations to obtain information about ionospheric variability around the North Geomagnetic Pole. In order to detect the ionospheric disturbances, 30-s observation data was used. The Rate of Total Electron Content Index was applied as a measure of the variability in the ionosphere. The first analyses were executed using more than 100 permanent stations. The results show two kinds of products: 2-hour maps in spherical geomagnetic coordinates and daily maps presenting the occurrence of the strong Total Electron Content fluctuations as a magnetic local time function, for the most disturbed days of April 2010. Apart from the main product of the algorithm, the Rate of Total Electron Content time series for individual satellite tracks was presented. The results demonstrated very good sensitivity of the obtained maps, which can detect even quite weak disturbances. The presented algorithm developed at the Geodynamic Research Laboratory of the University of Warmia and Mazury, in cooperation with Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation, will be applied in the near future to create near-real time service of the conditions in the ionosphere based on the Global Navigation Satellite Systems observations.     

Seasonal dependence of TEC and SLAB thickness

Several years of hourly daily GPS measurements of the vertical total electron content (TEC) and of the equivalent slab thickness made at different European locations are analysed by using the linear regression technique to demonstrate the response of these two ionospheric parameters to seasonal variations. It is found that both TEC and slab thickness are highly correlated with season. Analytical relationships are determined expressing the seasonal dependence of the vertical TEC and of the equivalent slab thickness as a function of the seasonal parameter cos χ at noon in each location.     

Ionospheric TEC disturbances over China during the strong geomagnetic storm in September 2017

From September 7 to 8, 2017, a G4-level strong geomagnetic storm occurred, which seriously impacted on the Earth’s ionosphere. In this work, the global ionospheric maps released by Chinese Academy of Sciences are used to investigate the ionospheric responses over China and its adjacent regions during the strong storm. The prominent TEC enhancements, which mainly associated with the neutral wind and eastward prompt penetration electric field, are observed at equatorial ionization anomaly crests during the main phase of the storm on 8 September 2017. Compared with those on 8 September, the TEC enhancements move to lower-latitude regions during the recovery phase on 9 September. A moderate storm occurred well before the start of the strong storm causes similar middle-latitude TEC enhancements on 7 September. However, the weak TEC depletion is observed at middle and low latitude on 9–10 September, which could be associated with the prevailing westward disturbance electric field or storm-time neural composition changes. In addition, the storm-time RMS and STD values of the ionospheric TEC grids over China increase significantly due to the major geomagnetic storm. The maximum of the RMS reaches 12.0 TECU, while the maximum of the STD reaches 8.3 TECU at ~04UT on 8 September.     

Comparison of GPS derived TEC with the TEC predicted by IRI 2012 model in the southern Equatorial Ionization Anomaly crest within the Eastern Africa region

We have compared the TEC obtained from the IRI-2012 model with the GPS derived TEC data recorded within southern crest of the EIA in the Eastern Africa region using the monthly means of the 5 international quiet days for equinoxes and solstices months for the period of 2012 – 2013. GPS-derived TEC data have been obtained from the Africa array and IGS network of ground based dual-frequency GPS receivers from four stations (Kigali (1.95°S, 30.09°E; Geom. Lat. 11.63°S), Malindi (2.99°S, 40.19°E; Geom. Lat. 12.42°S), Mbarara (0.60°S, 30.74°E; Geom. Lat. 10.22°S) and Nairobi (1.22°S, 36.89°E; Geom. Lat. 10.69°S)) located within the EIA crest in this region. All the three options for topside Ne of IRI-2012 model and ABT-2009 for bottomside thickness have been used to compute the IRI TEC. Also URSI coefficients were considered in this study. These results are compared with the TEC estimated from GPS measurements. Correlation Coefficients between the two sets of data, the Root-Mean Square Errors (RMSE) of the IRI-TEC from the GPS-TEC, and the percentage RMSE of the IRI-TEC from the GPS-TEC have been computed. Our general results show that IRI-2012 model with all three options overestimates the GPS-TEC for all seasons and at all stations, and IRI-2001 overestimates GPS-TEC more compared with other options. IRI-Neq and IRI-01-corr are closely matching in most of the time. The observation also shows that, GPS TEC are underestimated by TEC from IRI model during noon hours, especially during equinoctial months. Further, GPS-TEC values and IRI-TEC values using all the three topside Ne options show very good correlation (above 0.8). On the other hand, the TEC using IRI-Neq and IRI-01- corr had smaller deviations from the GPS-TEC compared to the IRI-2001.     

Analysis of the data processing strategies of spherical harmonic expansion model on global ionosphere mapping for moderate solar activity

Spherical harmonic (SH) expansion is widely used to model the global ionosphere map (GIM) of vertical total electron content (VTEC). According to the impact of different data processing methods of the SH expansion model on the VTEC maps, we specifically performed comprehensive analysis in terms of the data sampling rate, the time resolution, the spherical harmonic degree, and the relative constraint. One month of GPS data (January in 2016) from the International GNSS (Global Navigation Satellite System) Service (IGS) network in a moderate ionospheric activity period at the descending phase of Solar Cycle 24 was processed. To improve the computational efficiency of the daily GIM generation, the data sampling rate of 5?min was recommended allowing the GIM precision loss within 0.10 TECU (total electron content unit). The global VTEC map could be better represented in temporal and spatial domains with higher time resolution and higher spherical harmonic degree, especially at low latitude bands and in the southern hemisphere. The GIM precision improvement was about 10.91% for 1-h and about 15.15% for 0.5-h compared with the commonly used 2-h time resolution. The use of spherical harmonic degree 17 or 20 instead of 15 could improve the precision by 3.19% or 6.06%. We also found that an optimal relative constraint had to be found experimentally considering both the GIM precision and the GIM root mean square (RMS) map.     

Full characterization of a compact 90Sr/90Y beta source for TID radiation testing

A new methodology for Total Ionizing Dose (TID) tests is proposed. It is based on the employment of an on-chip ⁹⁰Sr/⁹⁰Y beta source as alternative to standard methods such as ⁶⁰Co gamma rays and electrons from LINAC. The use of a compact beta source for TID tests has several advantages. In particular, the irradiation of devices with more than one radiation source results in a better representation of the complex space radiation environment composed of several types, energies and dose-rates. In addition, the use of an easy handling beta source allows the irradiation of electronic devices without any damage to other auxiliary circuit. In this work, ⁹⁰Sr/⁹⁰Y beta source dosimetry and related radiation field characteristics are discussed in depth.In order to validate the proposed source for TID tests, a rather complex device such as the “SPC56EL70L5” microcontroller from ST-Microelectronics was exposed to ⁹⁰Sr/⁹⁰Y beta rays. The results of this test were compared to that of a previous test of another sample from the same lot with a standard gamma ⁶⁰Co source. The electronic performances following the two irradiations have been found to be in excellent agreement, by demonstrating therefore the validity of the proposed beta source for TID tests.     

GNSS观测数据ZTD建模的质量控制方法

针对目前基于GNSS观测数据的对流层天顶总延迟(ZTD)模型缺乏有效质量控制手段的现状,提出了一套综合考虑数据量、网格分辨率以及模型稳定性的ZTD建模质量控制方法,并采用内华达大地测量实验室(NGL)解算的高空间分辨率GNSS对流层数据,选取了近十年德国及周边区域[47°N-55°N,5°E-15°E]183个测站的实测ZTD,对该方法进行了校验。实验结果表明:在该质量控制方法下建立的新模型精度稳定,平均均方根误差(RMS)为3.4 cm,相对于UNB3m、EGNOS、GPT2w+Saas平均改善了42.4%、35.8%、33.3%。本文提出的质量控制方法有效提升了基于GNSS观测数据的ZTD模型的性能,对于ZTD建模研究具有一定的参考价值。     

空间CCD图像传感器辐射损伤评估方法

CCD图像传感器作为高灵敏度光电集成部件,易受空间辐射的影响而发生性能退化和工作异常。开展其辐射效应评价研究并制定相应的防护对策,是保证其在空间可靠应用的前提。文章通过地面模拟试验和辐射屏蔽计算,对空间用CCD图像传感器电离辐射损伤与位移损伤效应开展评估方法研究,为CCD抗辐射加固设计与地面评估试验提供参考。该方法也可用于其他光电器件和材料辐射效应评价。