The dual frequency radio signals of the Global Positioning System (GPS) allow measurements of the total number of electrons, called total electron content (TEC), along a ray path from GPS satellite to receiver. We have developed a new technique to construct two-dimensional maps of absolute TEC over Japan by using GPS data from more than 1000 GPS receivers. A least squares fitting procedure is used to remove instrumental biases inherent in the GPS satellite and receiver. Two-dimensional maps of absolute vertical TEC are derived with time resolution of 30 seconds and spatial resolution of 0.15° × 0.15° in latitude and longitude. Our method is validated in two ways. First, TECs along ray paths from the GPS satellites are simulated using a model for electron contents based on the IRI-95 model. It is found that TEC from our method is underestimated by less than 3 TECU. Then, estimated vertical GPS TEC is compared with ionospheric TEC that is calculated from simultaneous electron density profile obtained with the MU radar. Diurnal and day-to-day variation of the GPS TEC follows the TEC behavior derived from MU radar observation but the GPS TEC is 2 TECU larger than the MU radar TEC on average. This difference can be attributed to the plasmaspheric electron content along the GPS ray path. This method is also applied to GPS data during a magnetic storm of September 25, 1998. An intense TEC enhancement, probably caused by a northward expansion of the equatorial anomaly, was observed in the southern part of Japan in the evening during the main phase of the storm.

A new technique for mapping of total electron content using GPS network in Japan

Urbanization is one of the most impactful human activities across the world today affecting the quality of urban life and its sustainable development. Urbanization in Africa is occurring at an unpr...

https://www.tandfonline.com/doi/pdf/10.1080/10095020.2020.1787800

Urban sprawl and its impact on sustainable urban development: a combination of remote sensing and social media data

. The differential code bias (DCB) of global navigation satellite systems (GNSSs) affects precise ionospheric modeling and applications. In this paper, daily DCBs of the BeiDou Navigation Satellite System (BDS) are estimated and investigated from 2-year multi-GNSS network observations (2013–2014) based on global ionospheric maps (GIMs) from the Center for Orbit Determination in Europe (CODE), which are compared with Global Positioning System (GPS) results. The DCB of BDS satellites is a little less stable than GPS solutions, especially for geostationary Earth orbit (GEO) satellites. The BDS GEO observations decrease the precision of inclined geosynchronous satellite orbit (IGSO) and medium Earth orbit (MEO) DCB estimations. The RMS of BDS satellites DCB decreases to about 0.2 ns when we remove BDS GEO observations. Zero-mean condition effects are not the dominant factor for the higher RMS of BDS satellites DCB. Although there are no obvious secular variations in the DCB time series, sub-nanosecond variations are visible for both BDS and GPS satellites DCBs during 2013–2014. For satellites in the same orbital plane, their DCB variations have similar characteristics. In addition, variations in receivers DCB in the same region are found with a similar pattern between BDS and GPS. These variations in both GPS and BDS DCBs are mainly related to the estimated error from ionospheric variability, while the BDS DCB intrinsic variation is in sub-nanoseconds.

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Assessment of BeiDou differential code bias variations from multi-GNSS network observations

Various scientific applications and services increasingly demand real-time information on the effects of space weather on Earth’s atmosphere. In this frame, the Royal Observatory of Belgium (ROB) takes advantage of the dense EUREF Permanent GNSS Network (EPN) to monitor the ionosphere over Europe from the measured delays in the GNSS signals, and provides publicly several derived products. The main ROB products consist of ionospheric vertical Total Electron Content (TEC) maps over Europe and their variability estimated in near real-time every 15 min on 0.5° × 0.5° grids using GPS observations. The maps are available online with a latency of ~3 min in IONEX format at ftp://gnss.oma.be and as interactive web pages at www.gnss.be. This paper presents the method used in the ROB-IONO software to generate the maps. The ROB-TEC maps show a good agreement with widely used post-processed products such as IGS and ESA with mean differences of 1.3 ± 0.9 and 0.4 ± 1.6 TECu respectively for the period 2012 to mid-2013. In addition, we tested the reliability of the ROB-IONO software to detect abnormal ionospheric activity during the Halloween 2003 ionospheric storm. For this period, the mean differences with IGS and ESA maps are 0.9 ± 2.2 and 0.6 ± 6.8 TECu respectively with maximum differences (>38 TECu) occurring during the major phase of the storm. These differences are due to the lower resolution in time and space of both IGS and ESA maps compared to the ROB-TEC maps. A description of two recent events, one on March 17, 2013 and one on February 27, 2014 also highlights the capability of the method adopted in the ROB-IONO software to detect in near real-time abnormal ionospheric behaviour over Europe. In that frame, ROB maintains a data base publicly available with identified ionospheric events since 2012.

/pdf/near-real-time-ionospheric-monitoring-over-europe-at-the-3s09dnkfdb.pdf

Near real-time ionospheric monitoring over Europe at the Royal Observatory of Belgium using GNSS data

We present a statistical attribution analysis of the changes in global annual average thermospheric mass density and ionospheric total electron content (TEC) between the cycle 22/23 solar minimum (which occurred at epoch 1996.4) and the prolonged cycle 23/24 minimum (2008.8). The mass density data are derived from orbital drag, and the TEC data are derived from ground-based GPS receivers. The interminima change in mass density was −36% relative to the 1996.4 yearly average. Considering each multiplicative forcing independently, lower average geomagnetic activity during the cycle 23/24 minimum produced an interminima density change of at least −14%, solar extreme ultraviolet (EUV) irradiance forcing produced a density change of −1% to −13%, and changes in thermospheric CO2 concentration produced a density change of −5%. There was essentially no interminima change in global TEC derived from ground-based GPS receivers or space-based altimeters, even though past behavior suggests that it should have changed −3% (0.2 TEC units (1 TECU = 1016 el m−2)) in response to lower geomagnetic activity and −1% to −9% (0.1–0.8 TECU) in response to lower EUV irradiance. There is large uncertainty in the interminima change of solar EUV irradiance; the mass density and TEC data suggest a plausible range of 0% to −6%.

Attribution of interminima changes in the global thermosphere and ionosphere

[1] A global background total electron content (TEC) model is built by using the Center for Orbit Determination of Europe (CODE) TEC data for full 13 years, 1999–2011 It describes the climatological behavior of the ionosphere under both its primary external driver, ie, the direct photo-ionization by incident solar radiation, and regular wave particularly tidal forcing from the lower atmosphere The model construction is based on the very different time scales of the solar cycle, seasonal, and diurnal TEC variabilities (at least an order of magnitude); this leads to modulations of shorter-period variabilities with periods of the longer ones Then the TEC spatial-temporal variability is presented as a multiplication of three separable functions The solar activity is described by both parameters: F107 and its linear rate of change KF while the seasonal variability is presented by sine functions including four subharmonics of the year The diurnal variability of the TEC model is described by 2D (longitude-time) sine functions with zonal wave numbers up to 4 and 4 subharmonics of the solar day The model offers TEC maps which depend on geographic coordinates (5°×5° in latitude and longitude) and UT at given solar activity and day of the year The presented background model fits to the CODE TEC input data with a zero systematic error and an RMS error of 3387 TECU It is able to reproduce the well-known ionospheric structures as Weddell Sea Anomaly and some longitudinal wave-like structures

/pdf/global-tec-maps-based-on-gnss-data-1-empirical-background-3hr4k6l61t.pdf

Global TEC maps based on GNSS data: 1. Empirical background TEC model

Daily sea level forecast at tide gauge Burgas, Bulgaria using artificial neural networks

The paper aims to present a concise overview of the current status of the national spatial data infrastructures (SDI) of the European Union (EU) member states combined with specific peculiarities for Bulgaria. Some major challenges within the progress of the EU SDIs establishing, which is regulated by the European Directive INSPIRE (Infrastructure for spatial information in Europe) toward establishment of a SDI for environmental policies and activities, are marked out. Available comparative analyses of the main indicators for metadata, data-sets, and data services provided by EU member states are briefly discussed as a special attention is given to the Bulgarian progress. Recent achievements on accelerating the process of implementing the recommendations of the INSPIRE Directive in Bulgaria are outlined.

https://tandfonline.com/doi/pdf/10.1080/10095020.2017.1323524

A brief overview of current status of European spatial data infrastructures − relevant developments and perspectives for Bulgaria

Assessing the natural risk is a major issue for the responsible risk management and the sustainable regional development of SouthWestern Bulgaria. The paper presents a fuzzy logic model for complex estimation of the natural risk in the SW Bulgaria region, based on the available information sources and the expert knowledge. The risk assessment problem is defined as a multicriterial task that evaluates several input variables (indicators for natural hazards). A hierarchical fuzzy logic system with four inputs and one output is designed in the Matlab software environment using Fuzzy Logic Toolbox and Simulink. The simulation investigations are done for five geographic areas in SW Bulgaria. The areas are ordered by the decreasing degree of complex natural risk. This fuzzy system is part of the Web Integrated Information System for risk management of natural disasters which will be developed.

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Fuzzy Logic Model for Natural Risk Assessment in SW Bulgaria

Millions of people are affected by natural and man-made disasters each year, among which women, children, elderly persons, people with disabilities or special needs, prisoners, certain members of ethnic minorities, people with language barriers, and the impoverished are the most vulnerable population groups in case of emergencies. Many national and international organizations are involved in Early Warning and Crisis Management training, particularly focused on the special target to safe children and improve their knowledge about disasters. The success of these efforts is based on providing the specific information about disaster preparedness and emergency in adapted for children educational materials, accompanied with simple illustrative explanations for easy and fast understanding of the disasters. The active participation of the children in the educational activities through appropriate presenting the information, short training seminars and entertaining games will increase their resilience and will contribute significantly to their preparedness and adequate response in emergency situations. This paper aims to present the conceptual framework of a project for establishing an Educational Disaster Centre (EDC) “Save the children life” at University of Architecture, Civil Engineering and Geodesy (UACEG), providing relevant justification of the necessity to organize such centre in Bulgaria and discussing good practices in Europe and worldwide for children' education and training in case of disastrous event. General concepts for educational materials and children training are shared. Appropriate equipment for the EDC is shortly described.

/pdf/conceptual-framework-for-educational-disaster-centre-save-2zitozca57.pdf

Lyubka Pashova

Papers

Global TEC maps based on GNSS data: 1. Empirical background TEC model

Daily sea level forecast at tide gauge Burgas, Bulgaria using artificial neural networks

A brief overview of current status of European spatial data infrastructures − relevant developments and perspectives for Bulgaria

Fuzzy Logic Model for Natural Risk Assessment in SW Bulgaria

Conceptual Framework for Educational Disaster Centre "save the Children Life"