Telecommunication:A blind spot in disaster resilience science, yet essential for disaster mitigation and recovery

During major natural disasters, such as Hurricane Katrina and the flooding of New Orleans (2005), the Nepal earthquake (2015) and Hurricane Irma on St. Maarten (2017), the failure of all telecommunication created a disaster within a disaster, causing chaos and seriously hampering mitigation measures during and directly after the event. Despite these and other examples, most of the models and impact chains drawn by scientist to investigate disaster events ignore the role of telecommunication failure that aggravates the situation in the field. Also, scientific tools to predict risks and support disaster management are often provided via internet links, ignoring the likelihood of them being inaccessible when they are needed most, due to a telecom blackout. It is therefore essential to draw more attention of researcher to the role of telecommunications in disaster impact chains, and to interact with telecommunication experts and emergency organizations in the field to better prepare for telecommunication failure during and after disasters

The impact of solar flares on HF communications

When launched vertically or nearly vertically, radio waves are reflected by the ionosphere when their frequency is lower than the maximum plasma frequency. They return to earth in directly around the transmitter, and cover the area around the transmitter, with continuous coverage directly from the transmitter up to several hundred kilometers. This is mechanism is called ‘Near Vertical Incidence Skywave (NVIS) propagation’. The signal strength in the entire area is the same, as if a high altitude platform was used to transmit these signals. As no such platform is needed, nor any ground-based network of towers and interconnections, this system is very well suited for ad-hoc communications in regions where no telecommunication infrastructure exists, or in areas where that infrastructure has been destroyed by natural disasters or human hostilities. The ionosphere behaves like an efficient reflector for these waves with frequencies of typically 3-10 MHz at midlatitudes, and up to 15 MHz in the tropical zones. Low power transmitters, with power well below 100 Watts, will provide good coverage of an area as wide as 400 by 400 km. Humanitarian organizations such as Médecins sans Frontières and UNICEF make extensive use of this technology in poor and remote regions, but also in war zones. The ionosphere, which has its peak plasma density at heights between 150 and 350 km, is sustained by solar radiation. During days of quiet space weather, the variation of the electron density in the ionosphere and hence its maximum plasma ionosphere, vary more or less predictably in a diurnal cycle, following the seasons, and the 11-year solar cycle. When, however, days of solar storms and other extraordinary solar events, the ionosphere reacts accordingly. Some of those effects impact systems that society depends on, with a risk of significant socioeconomic impact [1]. One such events, the solar X-ray flare, has a strong and detrimental impact on ionospheric radio wave propagation, as the absorption in the D-layer of the ionosphere increases abruptly. While this phenomenon is well-known, we have been able to document its effect in detail with modern instruments during a scientific experiment investigating characteristic wave dual-polarization diversity, showing the impact radio wave path loss, both the ordinary and extraordinary waves, as well as the ambient electromagnetic noise arriving via the ionosphere [2]. This also provides evidence that in quiet rural areas, where local noise ‘smog’ is absent, 97% of the ambient noise field strength originates from remote source, and is transported via ionospheric propagation

Near Vertical Incidence Skywave propagation measurements duplicated in Spain and The Netherlands

(Report on a completed Short-Term Scientific Mission (STSM) funded by EurAAP) The ionosphere – under influence of the earth magnetic field – splits linearly polarized waves into two circularly polarized waves with opposite rotation sense [1]: magneto-ionic propagation. Our previous empirical NVIS research [2-4] has shown that that two orthogonal (physical) propagation channels can be created using dual circular polarization antennas, potentially doubling channel capacity. All previous measurements where performed on a 110 km long North-South path in The Netherlands (53ºN). To prove that the concept is not limited to specific azimuth angles and distances, the following experiment was designed: Multiple (4-8) beacon transmitters are set-up at random azimuth angles and random distances between 50 and 200 km around a single receiver site, the transmitters operating at a frequency around 7 MHz. Each beacon switches between Right Hand Circular Polarization (RHCP), Left hand Circular Polarization (LHCP) and linear polarization every 12 seconds. The signal of all beacons is recorded using a high-end digital receiver with 2 coherent antenna inputs, connected to two orthogonal dipoles. From this raw data, simultaneous reception of RHCP, LHCP and linear polarizations can be created. Isolation between the LHCP and RHCP channels will be calculated for each instant in time. The experiment is considered successful when more than 20 dB isolation is achieved. Possible improvement with adaptive elliptical polarization will be studied. Also the fading on the RHCP, LHCP and linearly polarized signals will be characterized and compared. The vertical angle of the earth’s magnetic field – which depends on the latitude of the location – is of influence on the magneto-ionic propagation. To prove that the experiment latitude is not critical to our earlier results, the experiment is first performed in The Netherlands (53ºN), then duplicated in Spain (41ºN), with the assistance of experts of the La Salle Ramon Llull University of Barcelona. Travel and lodging costs for this cooperation are sponsored by the European Association on Antennas and Propagation (EurAAP) through their Short-Term Scientific Mission (STSM) program, which stimulates cooperation between propagation experts of different European countries

Rapid and Accurate Measurement of Polarization and Fading of Weak VHF Signals Obliquely Reflected from Sporadic-E Layers

In the E-region of the ionosphere, at heights between 90 and 130 km, thin patches of enhanced ionization occur intermittently. The electron density in these sporadic-E (Es) clouds can sometimes be so high that radio waves with frequencies up to 150 MHz are obliquely reflected. While this phenomenon is well known, the reflection mechanism itself is not well understood. To investigate this question, an experimental system has been developed for accurate polarimetric and fading measurements of 50 MHz radio waves obliquely reflected by mid-latitude Es layers. The overall sensitivity of the system is optimized by reducing environmental electromagnetic noise, giving the ability to observe weak, short-lived 50 MHz Es propagation events. The effect of the ground reflection on observed polarization is analyzed and the induced amplitude and phase biases are compensated for. It is found that accurate measurements are only possible below the pseudo-Brewster angle. To demonstrate the effectiveness of the system, initial empirical results are presented which provide clear evidence of magneto-ionic double refraction

Corrigendum: A Pipeline for Volume Electron Microscopy of the Caenorhabditis elegans Nervous System.

[This corrects the article DOI: 10.3389/fncir.2018.00094.]

A Pipeline for Volume Electron Microscopy of the Caenorhabditis elegans Nervous System.

The "connectome," a comprehensive wiring diagram of synaptic connectivity, is achieved through volume electron microscopy (vEM) analysis of an entire nervous system and all associated non-neuronal tissues. White et al. (1986) pioneered the fully manual reconstruction of a connectome using Caenorhabditis elegans. Recent advances in vEM allow mapping new C. elegans connectomes with increased throughput, and reduced subjectivity. Current vEM studies aim to not only fill the remaining gaps in the original connectome, but also address fundamental questions including how the connectome changes during development, the nature of individuality, sexual dimorphism, and how genetic and environmental factors regulate connectivity. Here we describe our current vEM pipeline and projected improvements for the study of the C. elegans nervous system and beyond

A realistic simulation framework to evaluate ionospheric tomography

Observation of the 3-dimensional (3-D) electron density of the ionosphere is useful to study large-scale physical processes in space weather events. Ionospheric data assimilation and ionospheric tomography are methods that can create an image of the 3-D electron density distribution. While multiple techniques have been developed over the past 30 years, there are relatively few studies that show the accuracy of the algorithms. This paper outlines a novel simulation approach to test the quality of an ionospheric tomographic inversion. The approach uses observations from incoherent scatter radar (ISR) scans and extrapolates them spatially to create a realistic ionospheric representation. A set of total electron content (TEC) measurements can then be simulated using real geometries from satellites and ground receivers. This data set, for which the ‘truth’ ionosphere is known, is used as input for a tomographic inversion algorithm to estimate the spatial distribution of electron density. The reconstructed ionospheric maps are compared with the truth ionosphere to calculate the difference between the images and the truth. To demonstrate the effectiveness of this simulation framework, an inversion algorithm called MIDAS (Multi-Instrument Data Analysis Software) is evaluated for three geographic regions with differing receiver networks. The results show the importance of the distribution and density of GPS receivers and the use of a realistic prior conditioning of the vertical electron density profile. This paper demonstrates that when these requirements are met, MIDAS can reliably estimate the ionospheric electron density. When the region under study is well covered by GPS receivers, as in mainland Europe or North America, the errors in vertical total electron content (vTEC) are smaller than 1 TECu (2–4%). In regions with fewer and more sparsely distributed receivers, the errors can be as high as 20–40%. This is caused by poor data coverage and poor spatial resolution of the reconstruction, which has an important effect on the calibration process of the algorithm.</p