Aviation Altitudes Research Articles

Relationship Between NM Data and Radiation Dose at Aviation Altitudes During GLE Events

AbstractGround‐level enhancements (GLEs) are sporadic events that signal the arrival of high fluxes of solar energetic particles (SEPs) that have been produced by solar eruptions. Ground‐level enhancement events are characterized by a significant increase in the count rate of ground‐based neutron monitors (NMs). The arrival of high‐energy SEPs in the atmosphere leads to an enhancement of the radiation environment, with the enhancement at aviation altitudes being particularly hazardous to human health as pilots, crew, and airline passengers can be subjected to dangerous levels of radiation during a GLE. Through the use of a currently expanding library of analyzed GLEs and the application of a newly developed atmospheric radiation model, both of which have been created in‐house, we found a strong statistically significant relationship between real‐time NM data during GLE events and the radiation doses at aviation altitudes. This result provides a strong scientific basis for the use of real‐time NM data as a proxy for radiation dose estimates during GLE events and aids in the development of future nowcasting models to help mitigate the dangerous impacts of future GLEs.

A review on radiation environment pathways to impacts: Radiation effects, relevant empirical environment models, and future needs

Space radiation affects every aspect of spacecraft design and operation. As a part of the ISWAT (International Space Weather Actions Teams, https://iswat-cospar.org/) effort, this paper provides a comprehensive review of space radiation environment models that are commonly used by the spacecraft design community to estimate radiation effects on systems/components. The types of radiation effects discussed in this paper are total dose (both for ionizing and for non-ionizing), single event effects (SEE), surface and internal charging, and radiation effects at aviation altitudes. For each effect, a brief overview of the effect is described, relevant environment models are discussed, and the currently understood gaps and future needs are summarized. This paper serves as the radiation environment pathway-to-impact paper in the overall ISWAT Roadmap development.

How can we simulate ionizing radiation at aviation altitudes from TGFs?

So-called thunderclouds, which are large dark clouds that are able to generate thunder and lightning, can act as natural particle accelerators, producing complex high-energy phenomena such as terrestrial gamma-ray flashes (TGFs) and gamma-ray glows. These events are often described through the mechanism of relativistic runaway electron avalanches (RREAs), cascades of high-energy electrons accelerated by atmospheric electric fields. Since the energies of the RREAs are up to several tens of MeV, they can also trigger nuclear reactions with atoms of the air and in the soil while entering the ground. Although these phenomena are intriguing, their lack of precise measurement and still not completely understood origins pose a significant challenge for assessing their impact on aviation safety. This paper introduces the project Research Centre of Cosmic Rays and Radiation Events in Atmosphere (CRREAT), aimed at providing measurements of TGFs, thunderstorm ground enhancements (TGEs), and other ionizing radiation phenomena during thunderstorms, as well as at aviation altitudes, stratosphere, and low Earth orbits (LEO). The paper argues that without accurate data on the origins and physical characteristics of TGEs and TGFs, it is impossible to reliably simulate their impact on aircraft crews and passengers. The paper also mentions how the general-purpose 3D Monte Carlo (MC) code PHITS can be used for future simulations and comparisons with measurements related to ionizing radiation phenomena in the atmosphere.

Enhanced Radiation Levels at Aviation Altitudes and Their Relationship to Plasma Waves in the Inner Magnetosphere

AbstractIt is believed that galactic cosmic rays and solar energetic particles are the two major sources of ionizing radiation. However, the radiation source may also be due to relativistic electrons that are associated with precipitation from the Van Allen radiation belts. In this study, we use Automated Radiation Measurements for Aerospace Safety (ARMAS) measurements to investigate the precipitation mechanism of energetic radiation belt electrons. ARMAS instruments are flown on agency‐sponsored (NASA, National Oceanic and Atmospheric Administration, National Science Foundation, Federal Aviation Administration, DOE) flights, commercial space transportation companies and airliners (>9 km) in automated radiation collection mode. We identified magnetic conjunction events between ARMAS and NASA's Van Allen Probes to study the highly variable, dynamic mesoscale radiation events observed by ARMAS instruments at aviation altitudes and their relationship to various plasma waves in the inner magnetosphere measured by the Van Allen Probes. The results show that there is a strong correlation between dose rates observed by ARMAS and plasmaspheric hiss wave power measured by the Van Allen Probes, but no such relationship with electromagnetic ion cyclotron waves and only a modest correlation with whistler mode chorus waves. These results suggest that the space environment could have a potentially significant effect on passenger safety.

Simulation of cosmic rays inside an aircraft: spectral perturbation and dose reduction due to aircraft structures and contents.

In this study, an intricate combinatorial geometry model of a Boeing 777-300ER aircraft was constructed for Monte Carlo transport simulations. The aircraft-induced perturbations of the energy spectra and effective doses of secondary cosmic rays at a typical civil aviation altitude (10km) were investigated on a component-by-component basis, which included neutrons, protons, photons, electrons, positrons, muons and charged pions. Two geomagnetic cutoff rigidities (1.35 and 15.53 GV) and two solar modulation parameters (430 and 1360 MV) were considered in the aforementioned simulations. The characteristics of various cosmic-ray components at six locations along the fuselage were assessed and compared with those of an unperturbed radiation field in the atmosphere. Aircraft structures and contents reduced the effective doses of personnel inside the aircraft to varying degrees, up to an ~32% reduction in the middle section of the passenger cabin. On average, the dose reduction was ~12-16% depending on geomagnetic and solar conditions. Quantifying the aircraft's self-shielding effects can further improve the estimation accuracy of aircrew and passengers' exposure to cosmic radiation. Information regarding the perturbed energy spectra of cosmic rays may be useful for designing onboard experiments or analyzing onboard measurement data.

Application of the global neutron monitor network for assessment of spectra and anisotropy and the related terrestrial effects of strong SEPs

Studies of the characteristic of strong solar energetic particles (SEPs), that is events that can be registered by ground-based instruments such as neutron monitors, allow one to understand their acceleration and propagation in interplanetary space and gives the necessary basis to quantify the related cosmic-ray-induced terrestrial effects. After solar eruptive processes, such as solar flares and/or coronal mass ejections, solar ions are accelerated to the high-energy range. In most cases, the energy of the accelerated solar ions reaches several tens of MeV/n, yet occasionally it exceeds 100 MeV/n or even reaches the GeV/n range. In the latter case, the energy of SEPs is enough, so that they induce an atmospheric particle shower, whose secondary particles reach the ground, eventually registered by ground-based detectors, specifically neutron monitors. This particular class of events is known as ground-level enhancements (GLEs). Here we present a full-chain scheme for assessment of spectra and anisotropy and the related terrestrial effects of GLE causing SEPs. We discuss the application of a method for analysis of GLEs using neutron monitor data and the employment of the derived spectra as a basis to quantify cosmic-ray-induced terrestrial effects during GLEs, specifically atmospheric ionization and exposure to secondary radiation (radiation dose) at cruising aviation altitudes. We present an example study of two GLEs, namely their SEP energy/rigidity spectra derived using records from the global NM network and models for quantification of the atmospheric ionization and exposure to radiation at flight altitudes (ambient dose) during the considered events.

The radiation environment over the African continent at aviation altitudes: first results of the RPiRENA-based dosimeter

The radiation environment over the African continent, at aviation altitudes, remains mostly uncharacterized and unregulated. In this paper, we present initial measurements made by a newly developed active dosimeter onboard long-haul flights between South Africa and Germany. Based on these initial tests, we believe that this low-cost and open-source dosimeter is suitable for continued operation over the African continent and can provide valuable long-term measurements to test dosimetric models and inform aviation policy.

Assessment of the radiation risk at flight altitudes for an extreme solar particle storm of 774 AD

Intense solar activity can lead to an acceleration of solar energetic particles and accordingly increase in the complex radiation field at commercial aviation flight altitudes. We considered here the strongest ever reported event, namely that of 774 AD registered on the basis of cosmogenic-isotope measurements, and computed the ambient dose at aviation altitude(s). Since the spectrum of solar protons during the 774 AD event cannot be directly obtained, as a first step, we derived the spectra of the solar protons during the ground level enhancement (GLE) #5 on 23 February 1956, the strongest event observed by direct measurements, which was subsequently scaled to the size of the 774 AD event and eventually used as input to the corresponding radiation model. The GLE #5 was considered a conservative approach because it revealed the hardest-ever derived energy spectrum. The global map of the ambient dose was computed under realistic data-based reconstruction of the geomagnetic field during the 774 AD epoch, based on paleomagnetic measurements. A realistic approach on the basis of a GLE #45 on 24 October 1989 was also considered, that is by scaling an event with softer spectra and lower particle fluxes compared to the GLE #5. The altitude dependence of the event-integrated dose at altitudes from 30 kft to 50 kft (9.1–15.2 km) was also computed for both scenarios. Our study of the radiation effects during the extreme event of 774 AD gives the necessary basis to be used as a reference to assess the worst-case scenario for a specific threat, that is radiation dose at flight altitudes.

A Detection Method of Atmospheric Neutron Profile for Single Event Effects Analysis of Civil Aircraft Design

High-energy particles such as neutron act as serious threats to electronic equipment on board aircraft via Single Event Effects (SEE), but atmospheric neutron flux profile which could cover civil aviation altitude is rarely observed. To address the representative of atmospheric radiation data in SEE analysis, we propose a new method of detecting atmospheric neutron profile for civil aviation altitude. Using the sounding balloon carrying one nuclear radiometer, the radiation dose could be observed with high accuracy. Subsequently, the profile of atmospheric neutron flux can be derived on the basis of the conversion equation between radiation dose and the neutron flux. We implement two experiments, and the results show that this low-cost method could reliably obtain the vertical distribution of atmospheric neutron and might be integrated into SEE analysis of civil aircraft design.

Monte Carlo simulation of semiconductor-based detector in mixed radiation field in the atmosphere

Calculation of radiation protection quantities in tissue equivalent material from measurements using semiconductor detectors requires correction factors for conversion of the measured values in the semiconductor material to the tissue equivalent material. This approach has been used many times in aircraft and for space dosimetry. In this paper, we present the results of Monte Carlo simulations which reveal the need to take into account both the radiation field and the detector material when performing the conversion of measured values to radiation protection quantities. It is shown that for low Z target material, most of the dose equivalent at aviation altitudes comes from neutrons originating from nuclear reactions, while in high Z targets most of the dose equivalent comes from photons, originating from electromagnetic reactions.

A Method for Calculating Atmospheric Radiation Produced by Relativistic Electron Precipitation

AbstractRadiation safety in the Earth's atmosphere is of particular importance to our living environment, especially at aviation altitudes. Aviation radiation has been long known to originate primarily from the galactic and solar system: galactic cosmic rays and solar energetic protons. Recent flight measurements by the Automated Radiation Measurements for Aerospace Safety experiment have uncovered another potential source for aviation radiation: Relativistic Electron Precipitation (REP) from the Van Allen radiation belts. REP can induce radiation at aviation altitudes through bremsstrahlung X‐ray production, which carries radiation down to the stratosphere and even the troposphere. In this study, using a suite of physics‐based Monte Carlo models, we characterize the effective radiation dose produced at altitudes between ground and low‐Earth‐orbit by relativistic precipitation electrons with energies between 100 keV and 10 MeV. We produce a lookup table of atmospheric radiation production that calculates the expected radiation dose for a given precipitation flux, spectrum, and pitch angle distribution. This lookup table provides results that are consistent with X‐ray measurements during radiation belt precipitation by balloon‐borne instruments in the stratosphere, and can be directly used to convert space‐borne measurements of precipitation fluxes into aviation radiation. This study represents our first attempt toward better understanding of REP's role in the atmospheric high‐altitude radiation environment.

Detecting Ground Level Enhancements Using Soil Moisture Sensor Networks

AbstractGround level enhancements (GLEs) are space weather events that pose a potential hazard to the aviation environment through single event effects in avionics and increased dose to passengers and crew. The existing ground level neutron monitoring network provides continuous and well‐characterized measurements of the radiation environment. However, there are only a few dozen active stations worldwide, and there has not been a UK‐based station for several decades. Much smaller neutron detectors are increasingly deployed throughout the world with the purpose of using secondary neutrons from cosmic rays to monitor local soil moisture conditions (COSMOS). Space weather signals from GLEs and Forbush decreases have been identified in COSMOS data. Monte Carlo simulations of atmospheric radiation propagation show that a single COSMOS detector is sufficient to detect the signal of a medium‐strength (10%–100% increase above background) GLE at high statistical significance, including at fine temporal resolution. Use of fine temporal resolution would also provide a capability to detect Terrestrial Gamma Ray Flashes (via secondary neutrons) which are produced by certain lightning discharges and which can provide a hazard to aircraft, particularly in tropical regions. We also show how the COsmic‐ray Soil Moisture Observing System‐UK detector network could be used to provide warnings at the International Civil Aviation Organization “Moderate” and “Severe” dose rate thresholds at aviation altitudes, and how multiple‐detector hubs situated at strategic UK locations could detect a small GLE at high statistical significance and infer crucial information on the nature of the primary spectrum.

Extensive study of radiation dose on human body at aviation altitude through Monte Carlo simulation

The diverse near-Earth radiation environment due to cosmic rays and solar radiation has direct impact on human civilization. In the present and upcoming era of increasing air transfer, it is important to have precise idea of radiation dose effects on human body during air travel. Here, we calculate the radiation dose on the human body at the aviation altitude, also considering the shielding effect of the aircraft structure, using Monte Carlo simulation technique based on Geant4 toolkit. We consider proper 3D mathematical model of the atmosphere and geomagnetic field, updated profile of the incoming particle flux due to cosmic rays and appropriate physics processes. We use quasi-realistic computational phantoms to replicate the human body (male/female) for the effective dose calculation and develop a simplified mathematical model of the aircraft (taking Boeing 777-200LR as reference) for the shielding study. We simulate the radiation environment at the flying altitude (at 10 km and considering geomagnetic latitude in the range of 45–50°), as well as at various locations inside the fuselage of the aircraft. Then, we calculate the dose rates in the different organs for both male and female phantoms, based on latest recommendations of International Commission on Radio logical Protection. This calculation shows that the sex-averaged effective dose rate in human phantom is 5.46 μSv/h, whereas, if we calculate weighted sum of equivalent dose contributions separately in female and male body: total weighted sum of equivalent dose rate received by the female phantom is 5.72 μSv/h and that by the male phantom is 5.20 μSv/h. From the simulation, we also calculate the numerous cosmogenic radionuclides produced inside the phantoms through activation or spallation processes which may induce long-term biological effects.

Cosmic-ray neutron fluxes and spectra at different altitudes based on Monte Carlo simulations

Cosmic-ray neutrons (CRNs) account for about half of the radiation dose received by airline crews and passengers at aviation altitudes. CRNs also comprise important background radiation near the ground, which should be considered in neutron counts for the purpose of nuclear safeguarding and homeland security. In this study, simulations were conducted with the Geant4 toolkit to describe the air shower of cosmic rays. The latest experimental driving models for the atmosphere, geomagnetic field, and primary galactic cosmic rays were applied in these simulations. The simulation was validated by comparing the results with those measured on the NASA ER-2 aircraft. the CRN fluxes and spectra were calculated at altitudes ranging from one to tens of kilometers. We determined the characteristics of the CRN spectra and analyzed their dependency on the altitude. To consider their impact on the local environment, the CRNs near the ground were modeled with a specific equivalent approach, which allowed the simulations to be conducted with limited computer processing power. The parameters for the incident primary CRNs near the ground were calculated by simulating the cosmic ray air shower. The modeling dimensions were considered for the air and ground, and an appropriate approximation solution was obtained. The model near the ground was used to investigate the dependences of the CRN flux and spectrum on the soil moisture.

Radiation Data Portal: Integration of Radiation Measurements at the Aviation Altitudes and Solar‐Terrestrial Environment Observations

AbstractThe impact of radiation dramatically increases at high altitudes in the Earth's atmosphere and in space. Therefore, monitoring and access to radiation environment measurements are critical for estimating the radiation exposure risks of aircraft and spacecraft crews and the impact of space weather disturbances on electronics. Addressing these needs requires convenient access to multisource radiation environment data and enhancement of visualization and search capabilities. The Radiation Data Portal represents an interactive web‐based application for search and visualization of in‐flight radiation measurements. The portal enhances the exploration capabilities of various properties of the radiation environment and provides measurements of dose rates along with information on space weather‐related conditions. The Radiation Data Portal back‐end is a MySQL relational database that contains the radiation measurements obtained from the Automated Radiation Measurements for Aerospace Safety (ARMAS) device and the soft X‐ray and proton flux measurements from the Geostationary Operational Environmental Satellite. The implemented application programming interface and Python routines allow a user to retrieve the database records without interaction with the web interface. As a use case of the Radiation Data Portal, we examine ARMAS measurements during an enhancement of the solar proton (SP) fluxes, known as solar proton events, and compare them to measurements during SP‐quiet periods.

A Comprehensive Approach for Estimating Collective and Average Effective Doses of Galactic Cosmic Radiation Received by Pilots.

This study proposes a feasible and comprehensive approach for estimating collective and average effective doses of galactic cosmic radiation received by pilots on the basis of data in publicly available civil aviation annual statistical reports. Large uncertainties are associated with the estimation of these quantities because the radiation environment at aviation altitudes is complex, and a large number of flights operated by various air carriers is involved. A best estimate can be obtained through this approach because it considers all passenger, cargo, and charter flights operated during a long period of time instead of subjectively selecting some representative flights for dose evaluation. The approach becomes feasible and practical with the aid of a special feature called automatic batch analysis in the NTHU Flight Dose Calculator. There are two international airlines in Taiwan: China Airlines and EVA Air. As a demonstration, the collective effective dose received by the 2,513 pilots from the two airlines in 2018 was estimated to be 4,947 person-mSv, and the average effective dose per pilot was 1.97 mSv. These estimates were considered representative because they were based on all 151,526 flight segments operated that year. The assessment of the annual effective doses received by pilots in Taiwan from 2006 to 2018 was performed. The results varied in the range of 1.70-2.97 mSv because of variations in solar activity and operational flight routes. A regression model that can effectively reproduce the derived average effective dose rates on board aircraft was obtained for future application in aircrew dosimetry.

Space Radiation and Plasma Effects on Satellites and Aviation: Quantities and Metrics for Tracking Performance of Space Weather Environment Models.

The Community Coordinated Modeling Center has been leading community‐wide space science and space weather model validation projects for many years. These efforts have been broadened and extended via the newly launched International Forum for Space Weather Modeling Capabilities Assessment (https://ccmc.gsfc.nasa.gov/assessment/). Its objective is to track space weather models' progress and performance over time, a capability that is critically needed in space weather operations and different user communities in general. The Space Radiation and Plasma Effects Working Team of the aforementioned International Forum works on one of the many focused evaluation topics and deals with five different subtopics (https://ccmc.gsfc.nasa.gov/assessment/topics/radiation-all.php) and varieties of particle populations: Surface Charging from tens of eV to 50‐keV electrons and internal charging due to energetic electrons from hundreds keV to several MeVs. Single‐event effects from solar energetic particles and galactic cosmic rays (several MeV to TeV), total dose due to accumulation of doses from electrons (>100 keV) and protons (>1 MeV) in a broad energy range, and radiation effects from solar energetic particles and galactic cosmic rays at aviation altitudes. A unique aspect of the Space Radiation and Plasma Effects focus area is that it bridges the space environments, engineering, and user communities. The intent of the paper is to provide an overview of the current status and to suggest a guide for how to best validate space environment models for operational/engineering use, which includes selection of essential space environment and effect quantities and appropriate metrics.

The upgraded GLE database includes assessment of radiation exposure at flight altitudes

The exposure to radiation due to cosmic rays at cruising aviation altitudes is an important topic in the field of space weather. While the effect of galactic cosmic rays can be easily assessed on the basis of recent models, assessments of the absorbed dose during strong solar particle events is rather complicated. A specific interest are events with energy about GeV/nucleon, which produce an atmospheric cascade registered by ground based detectors e.g. neutron monitors. Those events are known as ground level enhancements (GLEs) and can significantly enhance the radiation exposure at flight altitudes over the polar regions. A recent upgrade of the existing GLE database provides information on the estimated solar protons energy/rigidity spectra, the corresponding computed effective doses and the used bibliography. Using information retrieved from this upgrade we performed statistical analysis of maximum effective doses at commercial flight altitude of 35 kft during several GLEs, where the necessary information as energy/rigidity spectra of the solar protons is available. For the computations a recent model for assessment of effective dose due to cosmic ray particles was employed. A highly significant correlation between the maximum effective dose rate and neutron monitor peak count rate increase during GLEs is observed. Here, we propose to use the maximal count rate increase as a proxy for assessment of the effective dose at flight altitude during strong solar particle events.

Measurement of UV radiation in commercial aircraft

Ultraviolet radiation (UVR) is significantly higher at aviation altitudes with respect to sea level. Cockpit windshields protect pilots from UV-B radiation but studies have shown that this is not necessarily the case for UV-A radiation. This work investigates the spectral properties of several windshields under flight conditions. Only one of the investigated windshields showed good UV-A attenuation. Furthermore, the altitude dependence of UV-A irradiance behind a windshield was measured with high spatial resolution. Measurements of the maximal UV irradiance behind the windshield surfaces and at the pilot’s position are compared to the recommendations by the International Commission on Non-Ionising Radiation Protection. Some recommended limits were exceeded at the surface of the windshields with direct sunlight and a large field of view. At the pilot’s position, with a more realistic field of view, the unweighted recommended level could have been exceeded within tens of minutes by looking in the direction of the Sun without visor or other protective measures. The weighted recommended maximal UVR exposure was not exceeded, neither with the use of the visor at the pilot’s position nor without it. The use of the visor for filtering direct sunlight was very effective in terms of UV-A reduction.

A simple method to monitor the dose rate of secondary cosmic radiation at altitude

Monitoring the ambient dose equivalent rate at aviation altitudes is an ambitious task, which requires sophisticated dosemeter systems and the possibility to carry out such measurements on board aircraft. A rather simple approach has been investigated in this study: soundings with weather balloons up to an altitude of 30 km. This paper summarises the measurements carried out between 2011 and 2016. The results indicate that annual measurements of the ambient dose equivalent rate at altitudes of around 20 km are a reliable tool to monitor the variation of the dose rate in the atmosphere owing to the solar activity.