Electron density plays an important role in the study of wave propagation and is known to be associated with the index of refraction and radiation belt diffusion coefficients. The primary objective of our investigation is to explore the possibility of implementing an onboard signal processing algorithm to automatically obtain electron densities from the upper hybrid resonance traces of wave spectrograms for future missions. U-Net, developed for biomedical image segmentation, has been adapted as our deep learning architecture with results being compared with those extracted from a more traditional semi-automated method. As a product, electron densities and cyclotron frequencies for the entire DSX mission between 2019 and 2021 are acquired for further analysis and applications. Due to limited space measurements, a synthetic image generator based on data statistics and randomization is proposed as an initial step toward the development of a generative adversarial network in hopes of providing unlimited realistic data sources for advanced machine learning. Plain Language Summary Electron density is the most important fundamental plasma parameter, however, it is very difficult to directly measure in situ due to spacecraft potential. A convolutional neural network (CNN), developed to recognize features from biomedical images, has been adapted to pull out the resonance traces from space wave receivers automatically specifying densities along satellite orbits. The comparison between computer vision based on a CNN and human vision based on a semi-automated extraction is demonstrated in this paper. With additional development and refinement, our proof-of-concept study may be matured to a level suitable for incorporation into onboard signal processing units to reduce human labor and human-in-the-loop induced operational errors during future space missions.

High-power transmission experiments in the very low frequency (VLF) mode have been conducted by the US Air Force Research Laboratory's Demonstration and Science Experiments (DSX) satellite in the radiation belts using a novel transmitter that automatically tunes to find the resonance frequency of the transmitter circuit including the antenna. The resulting voltage-frequency curves are used to derive antenna impedance at the resonance. The analysis shows that the antenna reactance is far less than that of a dipole antenna in free space. The derived radiation resistance is up to several tens of kilo Ohms. Most interestingly, it is found that the radiation resistance is inversely proportional to the square of transmission wave frequency. The transmitted power can be up to 80 W for the DSX transmitter with an 82-m long tip-to-tip antenna, showing that the high-power VLF transmission is feasible. Whistler wave transmission inside the higher-density plasmasphere is more efficient. Data analysis indicates that the antenna impedance does not vary systematically with the antenna orientation angle relative to the ambient magnetic field. The previous dominant theoretical studies yield not only incorrect values of the impedance but a completely different frequency dependence than that derived from DSX experiments. Instead, the recent theories correctly capture both the antenna impedance magnitude and the frequency dependence.

Plasma frequency is a fundamental parameter in the space plasma environment and is most accurately derived from in-situ wave receivers. Although semi-automated methodologies have been developed for use with post-processed data to extract the upper hybrid resonances from dynamic spectrograms, these such tools require significant attention from trained operators as a man-in-the-loop. Pattern recognition/image classification is an ideal technology to resolve such problem. Initial results from the signal identification algorithm developed at AFRL demonstrate its utility in solving an outstanding problem dating to the beginning of space age. Once proven successful, the fully automated application can be modified to provide space measurements as input for any assimilative model significantly improving predictive capabilities. Similar algorithms can be tailored to support future mission with similar wave receivers.

Very low frequency (VLF) waves (about 3–30 kHz) in the Earth’s magnetosphere interact strongly with energetic electrons and are a key element in controlling dynamics of the Van Allen radiation belts. Bistatic very low frequency (VLF) transmission experiments have recently been conducted in the magnetosphere using the high-power VLF transmitter on the Air Force Research Laboratory’s Demonstration and Science Experiments (DSX) spacecraft and an electric field receiver onboard the Japan Aerospace Exploration Agency’s Arase (ERG) spacecraft. On 4 September 2019, the spacecraft came within 410 km of each other and were in geomagnetic alignment. During this time, VLF signals were successfully transmitted from DSX to Arase, marking the first successful reception of a space-to-space VLF signal. Arase measurements were consistent with field-aligned propagation as expected from linear cold plasma theory. Details of the transmission event and comparison to VLF propagation model predictions are presented. The capability to directly inject VLF waves into near-Earth space provides a new way to study the dynamics of the radiation belts, ushering in a new era of space experimentation. Graphical Abstract

This study presents results from magnetic field line conjunctions between the medium‐Earth orbiting Demonstration and Science Experiments (DSX) satellite and the low‐Earth orbiting (LEO) very low frequencies (VLF) Propagation Mapper (VPM) satellite. DSX transmitted at VLF toward VPM, which was equipped with a single‐axis dipole electric field antenna, when the two spacecraft passed near the same magnetic field line. VPM did not observe DSX signals in any of the 27 attempted conjunction experiments; the goal of this study, therefore, is to explain why DSX signals were not received. Explanations include (a) the predicted power at LEO from DSX transmissions was too low for VPM to observe; (b) VPM's trajectory missed the “spot” of highest intensity due to the focused ray paths reaching LEO; or (c) rays mirrored before reaching VPM. Different combinations of these explanations are found. We present ray‐tracing analysis for each conjunction event to predict the distribution of power and wave normal angles in the vicinity of VPM at LEO altitudes. We find that, for low‐frequency (below 4 kHz) transmissions, nearly all rays mirror before reaching LEO, resulting in low amplitudes at LEO. For mid‐ and high‐frequency transmissions (∼8 and 28 kHz respectively), the power at LEO is above the noise threshold of the VPM receiver (between 0.5 μV/m and 1 μV/m). We conclude that the antenna efficiency and plasmasphere model are critical in determining the predicted power at LEO, and are also the two most significant sources of uncertainty that could explain the apparent discrepancy between predicted amplitudes and VPM observations.

Earth and Space Science Open Archive PosterOpen AccessYou are viewing the latest version by default [v1]The long term data plan for the DSX missionAuthorsYi-JiunSuiDIoanVladJennySanchezWilliamJohnstonMichaelStarksiDSee all authors Yi-Jiun SuiDCorresponding Author• Submitting AuthorAir Force Research Laboratory AlbuquerqueiDhttps://orcid.org/0000-0002-0407-3691view email addressThe email was not providedcopy email addressIoan VladAtmospheric and Environmental Researchview email addressThe email was not providedcopy email addressJenny SanchezAFRLview email addressThe email was not providedcopy email addressWilliam JohnstonAir Force Research Laboratoryview email addressThe email was not providedcopy email addressMichael StarksiDAFRL/RVBXiDhttps://orcid.org/0000-0001-8575-1855view email addressThe email was not providedcopy email address

Energetic electrons have occasionally been observed with high intensity in the low-latitude quasi-trapping region, below the inner radiation belt, where their intensity is normally low. During magnetic storms in November 2004 and July 2006, electrons reached magnetic drift shells with L < 1.1. Data from the IDP electron spectrometer on the DEMETER satellite provide high energy resolution, while multiple NOAA/POES satellites provide local time coverage. After accounting for instrumental effects caused by the high intensity, electron kinetic energy is shown to reach at least 200 keV with generally softer spectra than are normally found in the stable trapping region. Electron injection from the inner belt by an enhanced convection electric field similar to 5 mV/m may explain the observations. This could provide remote testing for models of global electrodynamics.

This paper describes version 1.5 of the AE9/AP9 family of space radiation climatology models. The most significant update is the inclusion of new data sets that change the flux maps. These new data include measurements from Van Allen Probes, Azur, and the HiLET sensor on the TWINS-2 spacecraft. In recognition of international contributions to the models, we introduce the IRENE nomenclature for International Radiation Environment Near Earth.

Clouds of vaporized samarium (Sm) were released during sounding rocket flights from the Reagan Test Site, Kwajalein Atoll in May 2013 as part of the Metal Oxide Space Cloud (MOSC) experiment. A network of ground-based sensors observed the resulting clouds from five locations in the Republic of the Marshall Islands. Of primary interest was an examination of the extent to which a tailored radio frequency (RF) propagation environment could be generated through artificial ionospheric modification. The MOSC experiment consisted of launches near dusk on two separate evenings each releasing similar to 6 kg of Sm vapor at altitudes near 170 km and 180 km. Localized plasma clouds were generated through a combination of photoionization and chemi-ionization (Sm + O. Sm+O -> SmO(+)e(-)) processes producing signatures visible in optical sensors, incoherent scatter radar, and in high-frequency (HF) diagnostics. Here we present an overview of the experiment payloads, document the flight characteristics, and describe the experimental measurements conducted throughout the 2 week launch window. Multi-instrument analysis including incoherent scatter observations, HF soundings, RF beacon measurements, and optical data provided the opportunity for a comprehensive characterization of the physical, spectral, and plasma density composition of the artificial plasma clouds as a function of space and time. A series of companion papers submitted along with this experimental overview provide more detail on the individual elements for interested readers.

Electron measurements from the Magnetic Electron Ion Spectrometer instruments on Van Allen Probes, for kinetic energies ∼100 to 400 keV, show characteristic dynamical features of the innermost ( L≲1.3 ) radiation belt: rapid injections, slow decay, and structured energy spectra. There are also periods of steady or slowly increasing intensity and of fast decay following injections. Local time asymmetry, with higher intensity near dawn, is interpreted as evidence for drift shell distortion by a convection electric field of magnitude ∼0.4 mV/m during geomagnetically quiet times. Fast fluctuations in the electric field, on the drift time scale, cause inward diffusion. Assuming that they are proportional to changes in Kp, the resulting diffusion coefficient is sufficient to replenish trapped electrons lost by atmospheric scattering. Major electric field increases cause injections by inward electron transport. An injection associated with the June 2015 magnetic storm is consistent with an enhanced field magnitude ∼5 mV/m. Subsequent drift echoes cause spectral structure.

A two-dimensional bounce-averaged test particle code was developed to examine trapped electron trajectories during geomagnetic storms with the assumption of conservation of the first and second adiabatic invariants. The March 2013 storm was selected as an example because the geomagnetic activity Kp index sharply increased from 2+to 7- at 6:00UT on 17 March. Electron measurements with energies between 37 and 460keV from the Magnetic Electron Ion Spectrometer (MagEIS) instrument onboard Van Allen Probes (VAP) are used as initial conditions prior to the storm onset and served to validate test particle simulations during the storm. Simulation results help to interpret the observed electron injection as nondiffusive radial transport over a short distance in the inner belt and slot region based on various electric field models, although the quantitative comparisons are not precise. We show that electron drift trajectories are sensitive to the selection of electric field models. Moreover, our simulation results suggest that the actual field strength of penetration electric fields during this storm is stronger than any existing electric field model, particularly for L <= 2.

Artificial Ionospheric Modification (AIM) can occur through deliberate or incidental injections of aerosols, chemicals or radio (RF) signals into the ionosphere. The Metal Oxide Space Clouds (MOSC) experiment was undertaken in April/May 2013 to investigate chemical AIM. Two sounding rockets were launched from Kwajalein Atoll and each released a cloud of vaporized samarium (Sm). The samarium created a localized plasma cloud that formed an additional ionospheric layer. The effects were measured by a wide range of ground based instrumentation, including optical and HF.