Study on Ionospheric Effects on SAR and their Statistics

The objective of this work is to study the impact of ionospheric disturbances on the Sentinel-1 mission. First we realize an ionospheric statistics database based on global TEC models and maps. Then we process interferometric stacks of Sentinel-1 images using the split-spectrum method to estimate the differential ionosphere and validate the GNSS based statistics. We use the newly developed database to determine the expected average and maximum ionospheric errors on Sentinel-1 SAR measurements. We discuss the possibility to routinely include flags or corrections for ionospheric disturbances in Sentinel-1 products

Precise ionospheric electron content monitoring from single-frequency GPS receivers

The number of existing global positioning system (GPS) single-frequency receivers continues growing. More than 90% of GPS receivers are implemented as low-cost single-frequency chipsets embedded in smartphones. This provides new opportunities, in particular for ionospheric sounding. In this context, we present the new sidereal days ionospheric graphic (SIg) combination of single-frequency GNSS measurements. SIg is able to monitor, for each given GNSS transmitter-receiver pair, the vertical total electron content (VTEC) relative to the previous observation with the same or almost the same line-of-sight (LOS) vector. In such arrangements the SIg multipath error mostly cancels, thus increasing the accuracy of the ΔVTEC significantly. This happens for the GPS constellation after one sidereal day (about 23 h 56 m) and for Galileo after 10 sidereal days approximately. Moreover, we show that the required calibration of the corresponding carrier phase ambiguity can be accurately performed by means of VTEC global ionospheric maps (GIMs). The results appear almost as accurate as those based on the dual-frequency technique, i.e., about 1 TECU or better, and with much more precision and resolution than the GIM values in the ionospheric region sounded by each given single-frequency receiver. The performance is demonstrated using actual data from 9 permanent GPS receivers during a total solar eclipse on August 21, 2017 over North America, where the corresponding ionospheric footprint is clearly detected in agreement with the total solar eclipse predictions. The advantages of extending SIg to lower carrier frequencies and the feasibility of applying it to other global navigation satellite system (GNSS) systems are also studied. This is shown in terms of a fully consistent VTEC depletion signature of the same eclipse phenomena, obtained with Galileo-only data in North America at mid and low latitude. Finally the SIg feasibility, including the cycle slip detection, is shown as well with actual mass-market single frequency GPS receivers at mid and high latitude

GNSS Solar Astronomy in real-time during more than one solar cycle

This work presents a summary of the continuous non-stop (hereinafter 24/7) real-time measurement and warning system for EUV solar activity, which is based on worldwide multifrequency Global Navigation Satellite Systems (GNSS) observations. The system relies on continuous tracking of the intensity of expected global patterns in the Earth’s ionosphere’s free electron distribution, which are associated with solar flares. The paper includes a discussion on the foundations of GNSS Solar Astronomy, along with details on its real-time implementation that began in 2011. Furthermore, a summary of the corresponding validation is provided, comparing it to external and direct solar EUV flux measurements obtained from SOHO-SEM. Finally, there will be a brief mention of the ongoing efforts to extend this technique to detect huge extra-solar sources

St. Patrick’s Day 2015 geomagnetic storm analysis based on Real Time Ionosphere Monitoring

A detailed analysis is presented for the days in March, 2015 surrounding St. Patrick’s Day 2015 geomagnetic storm, based on the existing real-time and near real-time ionospheric models (global or regional) within the group, which are mainly based on Global Navigation Satellite Systems (GNSS) and ionosonde data. For this purpose, a variety of ionospheric parameters is considered, including Total Electron Content (TEC), F2 layer critical frequency (foF2), F2 layer peak (hmF2), bottomside halfthickness (B0) and ionospheric disturbance W-index. Also, ionospheric high-frequency perturbations such as Travelling Ionospheric Disturbances (TIDs), scintillations and the impact of solar flares facing the Earth will be presented to derive a clear picture of the ionospheric dynamicsPostprint (published version

Precise ionospheric electron content monitoring from single-frequency GPS receivers

The number of existing global positioning system (GPS) single-frequency receivers continues growing. More than 90% of GPS receivers are implemented as low-cost single-frequency chipsets embedded in smartphones. This provides new opportunities, in particular for ionospheric sounding. In this context, we present the new sidereal days ionospheric graphic (SIg) combination of single-frequency GNSS measurements. SIg is able to monitor, for each given GNSS transmitter-receiver pair, the vertical total electron content (VTEC) relative to the previous observation with the same or almost the same line-of-sight (LOS) vector. In such arrangements the SIg multipath error mostly cancels, thus increasing the accuracy of the ΔVTEC significantly. This happens for the GPS constellation after one sidereal day (about 23 h 56 m) and for Galileo after 10 sidereal days approximately. Moreover, we show that the required calibration of the corresponding carrier phase ambiguity can be accurately performed by means of VTEC global ionospheric maps (GIMs). The results appear almost as accurate as those based on the dual-frequency technique, i.e., about 1 TECU or better, and with much more precision and resolution than the GIM values in the ionospheric region sounded by each given single-frequency receiver. The performance is demonstrated using actual data from 9 permanent GPS receivers during a total solar eclipse on August 21, 2017 over North America, where the corresponding ionospheric footprint is clearly detected in agreement with the total solar eclipse predictions. The advantages of extending SIg to lower carrier frequencies and the feasibility of applying it to other global navigation satellite system (GNSS) systems are also studied. This is shown in terms of a fully consistent VTEC depletion signature of the same eclipse phenomena, obtained with Galileo-only data in North America at mid and low latitude. Finally the SIg feasibility, including the cycle slip detection, is shown as well with actual mass-market single frequency GPS receivers at mid and high latitude

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 receive