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• A novel approach for regional ionosphere grid model with high spatial-temporal resolution is suggested. • The results of the new model is analyzed at different disturb geomagnetic and solar conditions. • A comparative analysis between the results of new model, GIM, NeQuick and GPS-TEC is made. In this paper, a novel approach based on C1 finite element (FE) interpolation is used to construct a regional ionospheric grid model (RIGM) with high spatio-temporal resolution over Europe. The spatial resolution of the new model is 0.50 for a longitude and latitude and a temporal resolution is 15 min. Observations of 38 GPS stations at different days and seasons with different geomagnetic and solar activity conditions are used to evaluate the new method. All stations are used to discretize the whole domain of the problem into separate triangular patches using a Delaunay triangulation algorithm. In this case, GPS stations would be the vertices of the triangular patches. Also, the position of stations in sun-fixed coordinate system with coordinates of latitude and longitude are chosen in order to consider the temporal variations of vertical total electron content (VTEC). To model the behavior of VTEC in each triangular patch, a particular shape function is defined which is fitted to VTEC values at three vertices of each triangle while it satisfies C1 continuity of VTEC at the common edges of the adjacent triangles. The results of the new model are compared with the VTEC of GPS at 4 control stations as well as global ionosphere map (GIM) and NeQuick models. Statistical parameters, including correlation coefficient, root mean square error (RMSE), standard deviation and dVTEC = |VTEC GPS - VTEC model | have been used to evaluate the error of the models. In low geomagnetic activity (KP < 4), the average RMSE at 4 control stations for FE, GIM and NeQuick models are 0.89, 1.05 and 6.42 TECU, respectively, while in the high geomagnetic activity (KP > 4), they are 1.24, 1.68 and 7.62 TECU, respectively. For further analysis, the accuracy of three models in precise point positioning (PPP) has been also evaluated. In PPP method, there is an improvement of about 1–16 mm compared to GIM and NeQuick models at coordinate components of control stations in high geomagnetic activity. The results of the analysis performed in this paper show that the FE model has a very high capability and accuracy in regional VTEC modeling in high and low geomagnetic conditions. The regional accuracy of this model is higher than GIM and NeQuick models and therefore can be considered as a new model for the ionosphere. [ABSTRACT FROM AUTHOR]

The ionospheric error affects the accuracy of the Global Navigation Satellite Systems observation and precise orbit determination. Usually, only the first order ionospheric error is considered, which can be eliminated by the ionospheric-free linear combination observation. But the remaining higher order ionospheric error will affect the accuracy of observations and their applications. In this paper, the influence of the higher order ionospheric error have been studied by using the International Geomagnetic Reference Field 13 and the Global Ionosphere Maps model produced by the Center for Orbit Determination in Europe. Focus on ionospheric error, the experiment of paper at doy 302 in 2019, which show that the second order ionospheric error impacting BeiDou Navigation Satellite System (BDS) B1I and B3I observation is 6.3569 mm and 11.8484 mm, respectively. Whereas, the third order ionospheric error impacting BDS B1I and B3I observation is 0.1734 mm and 0.3977 mm, respectively. Due to the current measurement accuracy of BDS carrier-phase observation can reach 2 mm, the influence of high order ionospheric error on observation should be considered. For BDS precise orbit determination, the orbit overlapping results are indicated that its orbit accuracy can be improved approximately 5 mm with the higher order ionospheric error correction, which is also in agreement with the results of Satellite Laser Ranging in this work. [ABSTRACT FROM AUTHOR]

As short-term variations existing in differential code bias of receivers (RDCB) will decrease the accuracies of extracting ionospheric observables by carrier-to-code leveling (CCL) method, a modified carrier-to code leveling (MCCL) method had been proposed to estimate RDCB offsets epoch by epoch in retrieval of ionospheric information. However, MCCL method is hampered by efficiency and precision at higher sampling intervals. To address RDCB offsets in higher sampling rate domain, a kernel model in the form of radial basis function (RBF) was chosen to model RDCB offsets produced by MCCL using lower sampling rate data in this paper. Owing to ill-posed problem induced by setting to many kernels, L1 norm regulation was employed to promote the sparsity of the problem and Fast iterative shrinkage thresholding algorithm (FISTA) was adopted to find the sparse solution. Data sets of 350 IGS stations evenly distributed in high-solar and low-solar activity years were chosen to illustrate the general existences of RDCB offsets and their dependence on solar activity. To validate the reliability and efficiency of the proposed method, two stations of them were selected out to construct the spares kernel model. As shown in experimental results, kernel model is of good performance in training data with over 90% sparsity rate and all standard deviations of the errors between original and fitting data are around 0.4 ns. It is a striking finding in terms of efficiency that the proposed method and CCL are much more efficient than MCCL in extracting ionospheric observables by means of fixed equipment. For further validations, generalized triangular series function (GTSF) was constructed using ionospheric observables derived from precise point positioning (PPP), CCL, MCCL and the proposed method. With Center for Orbit Determination in Europe (CODE) Global Ionospheric Map (GIM) regarded as reference, compared with VTEC estimates derived from CCL, those derived from MCCL and the proposed method have improved accuracies ranging from 10% to 20%. Overall, these results indicate that the proposed method has a promising application in retrieval of ionospheric observables in terms of accuracy and efficiency. [ABSTRACT FROM AUTHOR]

• Spatial and temporal variability of Es layer top frequency was analyzed. • Statistic Es layer top frequency at different seasons and phase of solar activity was performed. • The maps of the distribution of Es layer top frequency were produced. • The "cloud" model of Es layer was implemented in NIM-RT propagation model for ionogram simulations. This paper describes a study of the daily and yearly variability of one of the main characteristics of sporadic E layers (Es), the critical frequency (foEs). Our analysis is based on ionograms recorded by GIRO network ionosondes. The study estimates the spatial and temporal variability of the Es layer parameters and generates their statistics at different seasons and phases of the solar cycle. In turn, the statistics of the Es layer parameters can provide an assessment of the capability of the HF propagation forecasting. Further, maps of the distribution of Es layer critical frequency are produced. This paper implements the "cloud" model of Es layer in HF propagation model (Northern Ionosphere Model & Ray Tracing, NIM-RT) that can accurately reproduce many features observed in experimental measurements. Within this framework, a number of vertical sounding ionograms with the presence of Es layer are simulated based on the NIM-RT software. [ABSTRACT FROM AUTHOR]

Ionospheric estimation is becoming more and more important for the new multifrequency positioning algorithms, since they can help to improve greatly the convergence time for acquiring a good positioning error. In this paper, an open source tool to estimate precise ionospheric estimates is presented, namely ESA UGI (Unified-GNSS-Ionosphere). The presentation is done jointly with a methodology to test ionospheric model using a modified NeQuick to generate synthetic data. The results with different option of the ESA UGI shows that it has a good performance below 1 TECU (Total Electron Content Units) in vTEC (vertical Total Electron Content) RMS (Root Mean Squared) for European networks, around 2 TECU in a well-covered African region and between 1 and 6 TECU globally with this synthetic data. It shows as well the capability of changing between different ionosphere models (voxel, multilayer and spherical harmonics) and configuration options. Finally, a test with uncombined PPP actual data is presented showing that instantaneous convergence below 30 cm in 3D RMS position error are achievable in a well sounded area in Europe. [ABSTRACT FROM AUTHOR]

In this paper will be described the procedure followed for the achievement of a short term three dimensional (3-D) electron density mapping of the ionosphere in the European area. It consists of three main steps: (1) foF2 and M ( 3000 ) F2 short-term forecasts, ( foF2 STF ) and ( M3000F2 STF ), are calculated at 12 ionospheric observatories scattered in the European area; (2) the values of foF2 STF and M3000F2 STF on a grid of equi-spaced points, ( foF2 STF , GP ) and ( M3000F2 STF , GP ), are calculated by means of an appropriate interpolation algorithm by using the foF2 STF and M3000F2 STF data; (3) foF2 STF , GP and M3000F2 STF , GP data ingestion into the IRI model is employed to produce a short term 3-D electron density mapping ( ST-3D-M ) of the ionosphere. The electron density profiles provided by the ST-3D-M and IRI models, were compared with the electron density profiles autoscaled by the Automatic Real-Time Ionogram Scaler with True-height (ARTIST) system, which are here considered as the truth profiles. The results of these comparisons, shown for a certain number of epochs during quiet-moderate geomagnetic-ionospheric conditions, in the truth-sites of Athens (38 ○ .0′N, 23 ○ .5′E), Chilton (51 ○ .5′N, −0 ○ .6′W), Dourbes (50 ○ .1′ N, 4 ○ .6′E), Pruhonice (50 ○ .0′N, 14 ○ .6′E), Rome (41 ○ .9′N, 12 ○ .5′E), and Tortosa (40 ○ .8′N, 0 ○ .5′E), indicate that the ST-3D-M as forecasting tool can be considered generally reliable. [ABSTRACT FROM AUTHOR]

This paper summarizes the current NEO-related activities within ESA’s Space Situational Awareness programme. It has successfully federated some existing European assets: The NEODyS system, focussing on the precise orbit computation and impact predictions; the physical properties database as initially set up by the European Asteroid Research Network (EARN), and a priority list which lists NEOs in need of observation. Additionally, several European telescopes are now regularly used for the follow-up and, in a limited way, survey of NEOs. Europe has also been actively involved in setting up a decision process on how to react to an imminent impact threat. And ESA is preparing for a possible asteroid deflection demonstration mission, in collaboration with NASA. [ABSTRACT FROM AUTHOR]

Abstract: Sea level changes are threatening the human living environments, particularly along the European Coasts with highly dense population. In this paper, coastal sea level changes in western and southern Europe are investigated for the period 1993–2011 using Global Positioning System (GPS), Tide Gauge (TG), Satellite Altimetry (SA), Gravity Recovery and Climate Experiment (GRACE) and geophysical models. The mean secular trend is 2.26±0.52mm/y from satellite altimetry, 2.43±0.61mm/y from TG+GPS and 1.99±0.67mm/y from GRACE mass plus steric components, which have a remarkably good agreement. For the seasonal variations, annual amplitudes of satellite altimetry and TG+GPS results are almost similar, while GRACE Mass+Steric results are a little smaller. The annual phases agree remarkably well for three independent techniques. The annual cycle is mainly driven by the steric contributions, while the annual phases of non-steric (mass component) sea level changes are almost a half year later than the steric sea level changes. [Copyright &y& Elsevier]

Abstract: Simultaneous GPS observations from about 150 stations of European Permanent Network (EPN) have been used for studying dynamics of latitudinal profiles and structure of mid-latitude ionospheric trough (MIT). For the analyses, the TEC maps over Europe were created with high spatial and temporal resolution. The latitudinal profiles were produced from TEC maps with one-hour interval for geographic latitude range from 35N to 75N. The structure of latitudinal profiles relates to the occurrence of the ionospheric trough. The location of the trough depends on season, local time, and both geophysical and geomagnetic conditions. The trough structure in GPS-TEC demonstrates a smooth shape. The trough occurrence as a distinguished structure is more distinct during winter. The relation of TEC in the trough minimum to the equator and polar walls amounted to a factor of 2–4. The diurnal, seasonal as well as storm-time dynamics of the latitudinal profiles and the trough-like structure during different geomagnetic conditions are also presented. Day by day snapshots demonstrate great variability of TEC profiles and MIT, essential changes of the ionosphere structure took place during a storm. Similarly to the F2 region trough, the position of the TEC trough shifts towards lower latitudes during disturbances. In the storm-time, the TEC trough was recognized during day-time at latitudes lower than 70N. This paper presents the statistics describing the dynamics of the trough location. [Copyright &y& Elsevier]

Abstract: The aim of this paper is to investigate various aspects of the International Reference Ionosphere (IRI) performance in European area and to evaluate its accuracy and efficiency for: long term prediction of the critical frequencies foF2 and the maximum usable frequencies (MUF); using storm-time correction option (ST); the total electron content (TEC) and the maximum observable frequency (MOF) updating. Data of foF2, TEC, MOF are related to 2005. It is obtained that median values of foF2 can be predicted with the mean error σ(med)∼ 0.49MHz. For median values of MUF absolute σ was 1.39MHz and relative σ r was 8.8%. For instanteneous values estimates are increased to 1.58σ(med) MHz for foF2 and could reach 3.84MHz for MUF. Using correction ST-option and TEC values provided ∼30% improvement but TEC seems to be more preferable. However, from considered parameters of the IRI updating (ST-factor, TEC, MOF) the best results were demonstrated by MOF. Using the IRI2007 to calculate TEC gives 20–50% improvement of TEC correspondence to experimental values but this improvement is not enough to treat TEC without the IRI model adaptation. [Copyright &y& Elsevier]

Abstract: Ionospheric disturbances are known to have adverse effects on the satellite-based communication and navigation. One particular type of ionospheric effects, observed during major geomagnetic storms and threatening the integrity performance of both ground-based and space-based GNSS augmentation systems, is the sharp increase/decrease in the ionospheric delay that propagates in horizontal direction, thus called for convenience ‘moving ionospheric wall’. This paper presents preliminary results from researching such anomalous ionospheric delay gradients at European middle latitudes during the storm events of 29 October 2003 and 20 November 2003. For the purpose, 30-s GPS data from the Belgian permanent network was used for calculating and analysing the slant ionospheric delay and total electron content values. It has been found that, during these two particular storm events, substantial gradients did occur in Europe although they were not so pronounced as in the American sector. [Copyright &y& Elsevier]

Abstract: This paper describes the evaluation and performance of the Medium Resolution Imaging Spectrometer (MERIS) Global Vegetation Index (MGVI) algorithm that is implemented in the MERIS ground segment as the primary land surface product. MGVI output values represent the Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) which acts as an indicator of the presence and state of the vegetation canopy. The retrieval algorithm was optimized to be insensitive to the overlying atmosphere, the underlying soil as well as angular effects, using radiative transfer models. This physically based approach for retrieving land biophysical parameters can be extended to a series of sensors; the resulting algorithms are designed to deliver similar geophysical products that are directly comparable and ultimately generate long time series of FAPAR. After presenting the MGVI algorithm, we analyze actual results by inter-comparing the FAPAR values derived from MERIS to similar products derived from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) that have been generated at the European Commission Joint Research Centre (EC-JRC). The FAPAR products derived from MERIS and SeaWiFS are compared on several dates in 2002 when both instruments simultaneously observed the same geographical regions. The consistency and temporal continuity of the products are then evaluated by comparing the time series of FAPAR values over local sites in Europe during the year 2003 from the two instruments. Finally, multi-annual FAPAR time series obtained by merging MERIS and SeaWiFS products demonstrate the feasibility of monitoring the state of land surfaces with FAPAR products before and after the European drought event in 2003. [Copyright &y& Elsevier]

Abstract: With ESA’s MiDiv project [] the exobiology group at the German Aerospace Centre (DLR) in Cologne started to investigate the microbial diversity found on spacecrafts and in assembly halls used by Europe []. So far this examination was limited to cultivable microorganisms, probably excluding the majority of organisms present. To approach the microbial diversity of uncultivable microorganisms, new methods, have to be implemented into the analysing process. Therefore, we describe in this paper the adaptation of an existing protocol (surface sampling with swabs) to be used with a method based on the detection of DNA-fragments by polymerase chain reaction (PCR). Our data indicate that it is feasible to adapt the standardized sample taking process to be used with the PCR-method. While using a classical swabbing/cultivation approach for the detection of microorganisms on a surface, two impairing factors have to be accounted for. First, not all bacteria present on a surface will be taken up by the swab and second, not all the bacteria taken up will be released again from the swab. This will lead to a diminished overall estimation of the microorganisms present on a surface. Our studies further suggested that the estimated data had to be corrected by a factor of 2–3 to correspond with the actual numbers of spores spotted. [Copyright &y& Elsevier]

Abstract: It is well known that as long as variations in the ionosphere follow regular patterns, the latest version of the International Reference Ionosphere IRI-2001 model estimates sufficiently accurate NmF2 and other parameters relevant for the ionospheric effects on radio wave propagation. During geomagnetic storms, it is desirable that for the IRI-2001 model to be tested against available observations. This paper presents the comparison of the IRI-2001-generated electron density (N(h)) profiles with those updated using measured values over European area during October and November 2003 geomagnetic super storms. Ionospheric stations involved in this study are Athens, Chilton, Rome, Juliusruh and Tromso. These stations provide real-time ionospheric characteristics and N(h) profiles regularly within the framework of the EU COST271 Action on “Effects of the upper atmosphere on terrestrial and earth-space communications”. Comparative analysis shows that significant discrepancies do exist predominantly during the storm main phase. The model not always estimates correctly the phase and the magnitude of intense geomagnetic storm effects on the daytime F2 layer peak electron density at different European latitudes. Results are discussed in the context of real-time N(h) profile updating capabilities and effectiveness. [Copyright &y& Elsevier]

Modelling and forecasting of ionospheric parameters is very useful for different radio communication purposes. As long as variations in the ionosphere form regular patterns, the empirical International Reference Ionosphere model, IRI 2000, provides sufficiently accurate corrections to the maximum electron density, NmF2, to predict the ionospheric effects on radio wave propagation. During geomagnetic storms, however, agreement between the IRI 2000 model and observations is still insufficient. This paper deals with the analysis of measured and model predicted F-region electron densities under quiet and disturbed conditions with the main emphasis placed on the distribution of the F1-region daytime ionisation. Available electron density profiles obtained from ionograms for selected periods from several European ionospheric stations (Pruhonice, Ebro, Arenosillo) were compared with IRI 2000 model results. Comparative analysis shows that discrepancies do exist predominantly during the storm main phase. The model predicted daytime electron densities at the fixed F1-region heights are closer to observed values during summer than winter. Dependences of D1 on solar activity and season are also analysed. [Copyright &y& Elsevier]

ESA''s cornerstone mission “ROSETTA” to comet 46P/Wirtanen will bring a 100 kg Lander (provided by an international European consortium) with a scientific payload of about 27 kg to the surface of the comet''s nucleus. After a first scientific sequence it will operate for a considerable fraction of the cometary orbit around the sun (between 3 AU and 2 AU). The Lander is an autonomous spacecraft, powered with solar cells and using the ROSETTA Orbiter as a telemetry relais to Earth. The main scientific objectives are the in-situ investigation of the chemical, elemental, isotopic and mineralogical composition of the comet, study of the physical properties of the surface material, analyze the internal structure of the nucleus, observe temporal variations (day/night cycle, approach to sun), study the relationship between the comet and the interplanetary matter and provide ground reference data for Orbiter instruments.Ten experiments with a number of sub-experiments are foreseen to fulfil these objectives.In this paper we present the current status of the instrumental development and the scientific capabilities of each of the experiments. [Copyright &y& Elsevier]