Rodrigo Romero

Formation of ionospheric irregularities over Southeast Asia during the 2015 St. Patrick's Day storm

We investigate the geospace response to the 2015 St. Patricks Day storm leveraging on instruments spread over Southeast Asia (SEA), covering a wide longitudinal sector of the low-latitude ionosphere. A regional characterization of the storm is provided, identifying the peculiarities of ionospheric irregularity formation. The novelties of this work are the characterization in a broad longitudinal range and the methodology relying on the integration of data acquired by Global Navigation Satellite System (GNSS) receivers, magnetometers, ionosondes, and Swarm satellites. This work is a legacy of the project EquatoRial Ionosphere Characterization in Asia (ERICA). ERICA aimed to capture the features of both crests of the equatorial ionospheric anomaly (EIA) and trough (EIT) by means of a dedicated measurement campaign. The campaign lasted from March to October 2015 and was able to observe the ionospheric variability causing effects on radio systems, GNSS in particular. The multiinstrumental and multiparametric observations of the region enabled an in-depth investigation of the response to the largest geomagnetic storm of the current solar cycle in a region scarcely reported in literature. Our work discusses the comparison between northern and southern crests of the EIA in the SEA region. The observations recorded positive and negative ionospheric storms, spread F conditions, scintillation enhancement and inhibition, and total electron content variability. The ancillary information on the local magnetic field highlights the variety of ionospheric perturbations during the different storm phases. The combined use of ionospheric bottomside, topside, and integrated information points out how the storm affects the F layer altitude and the consequent enhancement/suppression of scintillations.

Benefits of GNSS software receivers for ionospheric monitoring at high latitudes

Ionospheric propagation is harmful for the electromagnetic signals broadcast by Global Navigation Satellite System (GNSS) satellites, mainly because of the presence of electron density anomalies. GNSS receivers are indeed of primary importance in scintillation and Total Electron Content (TEC) monitoring, especially at low and high latitudes, where scintillations are more frequent. Professional dual frequency custom hardware Global Positioning System (GPS) receivers have been successfully exploited since years as measurement tools able to provide post-correlation data that are then used for modeling the atmospheric phenomena. Recent trends in scientific GPS receivers implementation consider Software Defined Radio (SDR) as a valuable technology that enables access to intermediate and low level receiver processing stages. With respect to commercial hardware tools, they provide a larger subset of observables related to the signal processing stages, as well as a high grade of flexibility and re-configurability, depending on the user needs. Such features enable the design and test of innovative ionosphere monitoring techniques.

Design of a robust receiver architecture for scintillation monitoring

Global Navigation Satellite Systems (GNSS) signals traversing small scale irregularities present in the ionosphere may experience fast and unpredictable fluctuations of their amplitude and phase. This phenomenon can seriously affect the performance of a GNSS receiver, decreasing the position accuracy and, in the worst scenario, also inducing a total loss of lock on the satellite signals. This paper proposes an adaptive Kalman Filter (KF) based Phase Locked Loop (PLL) to cope with high dynamics and strong fading induced by ionospheric scintillation events. The KF based PLL self-tunes the covariance matrix according to the detected scintillation level. Furthermore, the paper shows that radio frequency interference can affect the reliable computation of scintillation parameters. In order to mitigate the effect of the interference signal and filter it out, a wavelet based interference mitigation algorithm has been also implemented. The latter is able to retrieve genuine scintillation indices that otherwise would be corrupted by radio frequency interference.

Ionosphere monitoring in South East Asia: Activities in GINESTRA and ERICA projects

GINESTRA and ERICA are two projects funded in the framework of the ALCANTARA Initiative of the European Space Agency. GINESTRA is a survey which aims to explore the capabilities of ionosphere monitoring in South East Asia to identify both institutions involved in this field and existing monitoring facilities. ERICA exploits the GINESTRA outcomes and aims to characterize the ionospheric variability of the Equatorial Ionospheric Anomaly in the region, in particular the variation of the plasma electron density in the southern and northern crests of the anomaly and over the dip equator identified by the Equatorial Ionospheric Trough. To achieve this goal, an ad hoc measurements campaign is conducted with ground-based instruments located in the footprints of the Equatorial Ionospheric Anomaly and of the Equatorial Ionospheric Trough in Vietnam and Indonesia. The paper presents the outcomes of GINESTRA and highlights some preliminary results of the data analysis conducted so far in the framework of ERICA.

Ionospheric scintillation threats to GNSS in polar regions: The DemoGRAPE case study in Antarctica

This paper addresses the design and implementation of an Ionospheric Scintillation Monitoring Receiver based on the Software Defined Radio paradigm. The monitoring platform exploits a digital data grabber and a GNSS fully software receiver, which grants a high level of flexibility for the processing strategy and the storage of raw samples of the signals in case of meaningful scintillation events. Such an implementation approach yields valuable advantages in critical areas, such as polar regions, where resources are limited and installation or maintenance and replacement of GNSS receivers may be critical. The paper describes the successful installations of the platforms in two Antarctic stations, providing results at the same quality level of professional GNSS receivers used for ionospheric scintillation monitoring.

Monitoring Ionosphere Over South America: The MImOSA and MImOSA2 projects

MImOSA and MImOSA2 are two projects funded in the framework of the ALCANTARA Initiative of the European Space Agency. MImOSA (Monitoring the Ionosphere Over South America) was a competence survey aimed at assessing the capabilities of the South American (SA) countries to monitor and investigate the ionosphere. This was done to understand how the currently existing facilities could be integrated with new GNSS-based installations to effectively support space weather activities in SA. The experience and the heritage acquired through MImOSA have led to a new project, MImOSA2 (Monitoring Ionosphere Over South America to support high precision applications), focused on technological applications and aimed at exploiting the data from selected facilities to support high-precision GNSS based services in SA. MImOSA2 is dedicated to the analysis, through an original method, of GNSS data acquired by a dense network of 50 Hz receivers to demonstrate the improvements on positioning accuracy when GNSS signal degradation due to harsh ionospheric conditions is taken into account. The multi-constellation capability of the adopted instrumentation allows generating ionospheric maps with a very fine spatial and temporal resolution to take into account the effects caused by the electron density irregularities. The synergy between European institutions and the Brazilian partner, and the use of newly dedicated algorithms offer the opportunity to demonstrate the improvements of positioning capability on long baseline RTK (Real Time Kinematic) and NRTK (Network RTK) (VRS approach) solutions in the considered region. Moreover, the effects of anthropogenic interference on GNSS L-band signals recorded in Presidente Prudente is under investigation, to evaluate the effects of environmental disturbances on GNSS derived measurements, by means of configurable communication devices and a software defined radio receiver.

A novel approach to ionospheric scintillation detection based on an open loop architecture

Ionospheric scintillation monitoring is becoming an increasing research activity in order to devise countermeasures to the harmful effects ionospheric activity has on positioning services based on Global Navigation Satellite Systems (GNSS). The amount of amplitude fluctuations in GNSS signals due to scintillation is estimated by the �������� index. For this purpose, traditional closed loop architectures are employed in the receiver. In this paper we investigate an alternative measurement parameter based on the Skewness of the histogram of the processed samples. The new metric could relay information akin to that of the S4 and it is estimated on an open loop receiver architecture.

Towards Analyzing the Effect of Interference Monitoring in GNSS Scintillation

Ionospheric Scintillation Monitoring Receivers (ISMR) are specialized GNSS receivers able to track and monitor scintillations in order to collect data that can be used to model the phenomenon, study its affects at receiver level and possibly predict its occurrence in the future. Such receivers are able to measure the amount of scintillation affecting a satellite signal in both amplitude and phase by making use of correlation data from the tracking processing blocks. This is normally done by computing two indices: the S4 for amplitude scintillation and the phase deviation due to scintillations [3]. However, as more telecommunication systems are likely to work in frequency bands close to GNSS signals in the next years, monitoring of scintillation activity might be threatened by the presence of Radio Frequency Interference (RFI) in the operation area. It is of interest to study the effects these systems may have on the estimation of scintillation indices due to unintentional leakages of power out of their allocated bandwidth [4]. Robust tracking of GNSS signals under such conditions must be guaranteed and it must also be ensured as best as possible that the typical scintillation indices are not affected by the additional error source

Effect of interference in the calculation of the amplitude scintillation index S4

Irregular electron content in the ionosphere affects the propagation of Global Navigation Satellite Systems (GNSS) signals with a phenomenon known as scintillation. Ionospheric scintillations are rapid fluctuations in the amplitude and phase of the signal that can lead a receiver to lose lock. In recent years the number of Ionospheric Scintillation Monitoring Receivers (ISMR) have increased dramatically. This paper presents an initial analysis of the effect that interference may have in the calculation of the widely used amplitude scintillation index S4. Interference is one of the growing threats to the performance of GNSS. Our analysis shows that interference may have particular effects on GNSS receivers that can lead them to output an erroneous measurement of the S4 index.