VTechWorks Repository :: Browsing by Author "England, Scott L."

Browsing by Author "England, Scott L."

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3D Simulator for Wind Interferometer Data-Model Comparison
Huda, Md Nurul (Virginia Tech, 2019-09-27)
The connection between earth and space weather has numerous impacts on spacecraft, radio communications and GPS signals. Thus, predicted & modeling this region is important, yet models (both empirical and first principles) do a poor job of characterizing the variability of this region. One of the main objectives of the NASA ICON mission is to measure the variability of the ionosphere and thermosphere at low-mid latitudes. The MIGHTI instrument on ICON is a Doppler Interferometer that measures the horizontal wind speed and direction with 2 discrete MIGHTI units, separated by 90˚, mounted on the ICON Payload Interface Plate. This work focuses on building a simulation of wind interferometer data, similar to MIGHTI, using a first-principles model as the input dataset, which will be used for early validation and comparison to the MIGHTI data. Using a ray-tracing approach, parameters like O, O2, O+, O2+, T, wind, solar F10.7 index will be read for every point along every ray from the model and brightness and Line of Sight (LOS) wind will be calculated as functions of altitude and time. These data will be compared to the MIGHTI observations to both to establish the limitation of such models, and to validate the ICON data. ICON will help determine the physics of our space environment and pave the way for mitigating its effects on our technology, communications systems and society. However, ICON is yet to launch and due to the unavailability of MIGHTI data, we have selected another instrument called WINDII (Wind Imaging Interferometer) from a different mission UARS (Upper Atmosphere Research Satellite) to demonstrate the utility of this data-model comparison. Similar to MIGHTI, WINDII measures Doppler shifts from a suite of visible region airglow and measures zonal and meridian winds, temperature, and VER (Volume Emission rate) in the upper mesosphere and lower thermosphere (80 to 300 km) from observations of the Earth's airglow. We will use a similar approach discussed for MIGHTI to calculate vertical profile of Redline airglow, Wind velocity, emission rate and compare them with our simulated results to validate our algorithm. We initially thought asymmetry calculation along the Line of Sight (LOS) would be the limiting factor. We believe there are other things going on such as variability in the winds associated with natural fluctuations in the thermosphere, atmospheric waves, inputs from the sun and the atmosphere below etc., appear to be bigger factor than just asymmetry along the line of sight.
Analysis of Ionospheric Data Sets to Identify Periodic Signatures Matching Atmospheric Planetary Waves
Norton, Andrew David (Virginia Tech, 2021-01-07)
Atmospheric planetary waves play a role in introducing variability to the low-latitude ionosphere. To better understand this coupling, this study investigates times when oscillations seen in both atmospheric planetary waves and ionospheric data-sets have similar periodicity. The planetary wave data-set used are temperature observations made by Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). These highlight periods during which 2-Day westward propagating wave-number 3 waves are evident in the mesosphere and lower thermosphere. The ionospheric data-set is Total Electron Content (TEC), which is used to identify periods during which the ionosphere appears to respond to the planetary waves. Data from KP and F10.7 indices are used to determine events that may be of external origin. A 17-year time-span from 2002 to 2018 is used for this analysis so that both times of solar minimum and maximum can be studied. To extract the periods of this collection of data a Morlet Wavelet analysis is used, along with thresholding to indicate events when similar periods are seen in each data-set. Trends are then determined, which can lead to verification of previous assumptions and new discoveries.
Analysis of Transfer Trajectories Utilizing Sequential Saturn-Titan Aerocaptures
Payne, Isaac Lee (Virginia Tech, 2023-07-03)
This thesis aims to investigate the potential of a transfer orbit using successive aerocaptures at Saturn and Titan to establish a science orbit around Titan. Titan is an Earth-like moon with a dense atmosphere and organic compounds present. It has many similarities with Earth that are useful to study such as superrotation. Superrotation is when the atmosphere rotates faster than the body it surrounds. In order to study Titan, we need to establish an orbit around it. The Saturn system is distant from Earth, 8.5 Astronomical Units (AU) which makes it difficult to reach from a time and velocity point of view. We propose to use an aerocapture at Saturn to intercept Titan with lower relative velocity in order to perform an aerocapture at Titan. The analysis was performed in primarily MATLAB to simulate the orbits. The results of this showed that we can aerocapture a spacecraft at Saturn and arrive at Titan within roughly 4 to 8 km/s relative velocity regardless of the incoming hyperbolic excess velocity at the Saturn system. This can be improve upon by using intermediate transfer orbits, such as bi-elliptics, to arrive with even lower relative velocities to Titan of as low as 1 km/s. The drag acceleration experienced during the Saturn aerocapture had peak values of between 0.2 and 1.4 g's and acceleration over 50% of the peak is experienced between 6.8 and 8 minutes. This capture method has the potential to make Titan more easily accessible and allow for scientific study of a clear target for improving our understanding of Earth-like processes on other bodies in our solar system.
Characterization and Modeling of Solar Flare Effects in the Ionosphere Observed by HF Instruments
Chakraborty, Shibaji (Virginia Tech, 2021-06-08)
The ionosphere is the conducting part of the upper atmosphere that plays a significant role in trans-ionospheric high frequency (HF, 3-30 MHz) radiowave propagation. Solar activities, such as solar flares, radiation storms, coronal mass ejections (CMEs), alter the state of the ionosphere, a phenomenon known as Sudden Ionospheric Disturbance (SID), that can severely disrupt HF radio communication links by enhancing radiowave absorption and altering signal frequency and phase. The Super Dual Auroral Radar Network (SuperDARN) is an international network of low-power HF coherent scatter radars distributed across the globe to probe the ionosphere and its relation to solar activities. In this study, we used SuperDARN HF radar measurements with coordinated spacecraft and riometer observations to investigate statistical characteristics and the driving mechanisms of various manifestations of solar flare-driven SIDs in HF observations. We begin in Chapter 2 with a statistical characterization of various effects of solar flares on SuperDARN observations. Simultaneous observations from GOES spacecraft and SuperDARN radars confirmed flare-driven HF absorption depends on solar zenith angle, operating frequency, and intensity of the solar flare. The study found flare-driven SID also affects the SuperDARN backscatter signal frequency, which produces a sudden rise in Doppler velocity observation, referred to as the ``Doppler flash'', which occurs before the HF absorption effect. In Chapter 3, we further investigate the HF absorption effect during successive solar flares and those co-occurring with other geomagnetic disturbances during the 2017 solar storm. We found successive solar flares can extend the ionospheric relaxation time and the variation of HF absorption with latitude is different depending on the type of disturbance. In Chapter 4, we looked into an inertial property of the ionosphere, sluggishness, its variations with solar flare intensity, and made some inferences about D-region ion-chemistry using a simulation study. Specifically, we found solar flares alter the D-region chemistry by enhancing the electron detachment rate due to a sudden rise in molecular vibrational and rotational energy under the inﬂuence of enhanced solar radiation. In Chapter 5, we describe a model framework that reproduces HF absorption observed by riometers. This chapter compares different model formulations for estimating HF absorption and discusses different driving influences of HF absorption. In Chapter 6, we have investigated different driving mechanisms of the Doppler flash observed by SuperDARN radars. We note two particular findings: (i) the Doppler flash is predominantly driven by a change in the F-region refractive index and (ii) a combination of solar flare-driven enhancement in photoionization, and changes in the zonal electric field and(or) ionospheric conductivity reduces upward ion-drift, which produces a lowering effect in the F-region HF radiowave reflection height. Collectively, these research findings provide a statistical characterization of various solar flare effects on the ionosphere seen in the HF observations, and insights into their driving mechanisms and impacts on ionospheric dynamics.
Combined Analysis of Hydrogen and Oxygen 102.6 nm Emission at Mars
Chaffin, Michael S.; Deighan, Justin; Jain, Sonal; Holsclaw, Greg; AlMazmi, Hoor; Chirakkil, Krishnaprasad; Correira, John; England, Scott L.; Evans, J. Scott; Fillingim, Matt; Lillis, Rob; Lootah, Fatma; Raghuram, Susarla; Eparvier, Frank; Thiemann, Ed; Curry, Shannon; AlMatroushi, Hessa (American Geophysical Union, 2022-08)
Water is lost from the Mars upper atmosphere to space as hydrogen and oxygen, both of which can be observed in scattered ultraviolet sunlight at 102.6 nm. We present Emirates Mars Mission Emirates Mars Ultraviolet Spectrometer (EMM/EMUS) insertion orbit observations of this airglow, resolving the independent altitude contributions of H and O for the first time. We present the first airglow modeling of the complete H and O 102.6 nm system and the first 3D azimuthally symmetric modeling of the O emission, retrieving temperatures and densities typical of northern spring. Our model reproduces the emission well above 200 km, but does not incorporate partial frequency redistribution needed to reproduce the observed O brightness at lower altitudes and on the disk. These results support future EMM/EMUS science orbit retrievals of H loss and the use of 102.6 nm observations to constrain planetary atmospheres across the solar system.
Computer Vision Tracking of sUAS From a Pan/Tilt Platform
Ogorzalek, Jeremy Patrick (Virginia Tech, 2019-06-24)
The ability to quickly, accurately, and autonomously identify and track objects in digital images in real-time has been an area of investigation for quite some time. Research in this area falls under the broader category of computer vision. Only in recent decades, with advances in computing power and commercial optical hardware, has this capability become a possibility. There are many different methods of identifying and tracking objects of interest, and best practices are still being developed, varying based on application. This thesis examines background subtraction methods as they apply to the tracking of small unmanned aerial systems (sUAS). A system combining commercial off-the-shelf (COTS) cameras and a pan-tilt unit (PTU), along with custom developed code, is developed for the purpose of continuously pointing at and tracking the motion of a sUAS in flight. Mixtures of Gaussians Background Modeling (MOGBM) is used to track the motion of the sUAS in frame and determine when to command the PTU. When the camera is moving, background subtraction methods are unusable, so additional methods are explored for filling this performance gap. The stereo vision capabilities of the system, enabled by the use of two cameras simultaneously, allow for estimation of the three-dimensional position and trajectory of the sUAS. This system can be used as a supplement or replacement to traditional tracking methods such as GPS and RADAR as part of a larger unmanned aerial systems traffic control (UTC) infrastructure.
Coupling Computationally Expensive Radiative Hydrodynamic Simulations with Machine Learning for Graded Inner Shell Design Optimization in Double Shell Capsules
Vazirani, Nomita Nirmal (Virginia Tech, 2022-12-29)
High energy density experiments rely heavily on predictive physics simulations in the design process. Specifically in inertial confinement fusion (ICF), predictive physics simulations, such as in the radiation-hydrodynamics code xRAGE, are computationally expensive, limiting the design process and ability to find an optimal design. Machine learning provides a mechanism to leverage expensive simulation data and alleviate limitations on computational time and resources in the search for an optimal design. Machine learning efficiently identifies regions of design space with high predicted performance as well as regions with high uncertainty to focus simulations, which may lead to unexpected designs with great potential. This dissertation focuses on the application of Bayesian optimization to design optimization for ICF experiments conducted by the double shell campaign at Los Alamos National Lab (LANL). The double shell campaign is interested in implementing graded inner shell layers to their capsule geometry. Graded inner shell layers are expected to improve stability in the implosions with fewer sharp density jumps, but at the cost of lower yields, in comparison to the nominal bilayer inner shell targets. This work explores minimizing hydrodynamic instability and maximizing yield for the graded inner shell targets by building and coupling a multi-fidelity Bayesian optimization framework with multi-dimensional xRAGE simulations for an improved design process.
Daily Variability in the Terrestrial UV Airglow
Immel, Thomas J.; Eastes, Richard W.; McClintock, William E.; Mende, Steven B.; Frey, Harald U.; Triplett, Colin C.; England, Scott L. (MDPI, 2020-09-30)
New capability for observing conditions in the upper atmosphere comes with the implementation of global ultraviolet (UV) imaging from geosynchronous orbit. Observed by the NASA GOLD mission, the emissions of atomic oxygen (OI) and molecular nitrogen (N2) in the 133–168-nm range can be used to characterize the behavior of these major constituents of the thermosphere. Observations in the ultraviolet from the first 200 days of 2019 indicate that the oxygen emission at 135.6 nm varies much differently than the broader Lyman-Birge-Hopfield (LBH) emission of N2. This is determined from monitoring the average instrument response from two roughly 1000 km2 areas, well separated from one another, at the same time of each day. Variations in the GOLD response to UV emissions in the monitored regions are determined, both in absolute terms and relative to a running 7-day average of GOLD measurements. We find that variations in N2 emissions in the two separate regions are significantly correlated, while oxygen emissions, observed in the same fixed geographic regions at the same universal time each day, exhibit a much lower correlation, and exhibit no correlation with the N2 emissions in the same regions. This indicates that oxygen densities in the airglow-originating altitude range of 150–200 km vary independently from the variations in nitrogen, which are so well correlated across the dayside to suggest a direct connection to variation in solar extreme-UV flux. The relation of the atomic oxygen variations to solar and geomagnetic activity is also shown to be low, suggesting the existence of a regional source that modifies the production of atomic oxygen in the thermosphere.
Development and Initial Testing of a Micro-Newton Torsion Pendulum with Gas-Dynamic Calibration
Smith, Brandon Joseph (Virginia Tech, 2019-03-05)
A novel torsion pendulum thrust test stand for micro-Newton-scale spacecraft thrusters is described. The stand is designed to be robust against electromagnetic interference effects internal or external to the thruster being tested. The design and testing of a gas-dynamic calibration thruster is included. This thruster is fully self-contained on the pendulum arm, with no external wires or feedlines connected to the device and impacting the dynamic response of the underlying pendulum. Initial calibration results are shown. Zero drift and hysteresis are present in the results, evidenced by a constant steady-state displacement drift and a return to a different displacement after shutdown of the calibration thruster. Results are compared to theoretical solutions of the equation of motion. An external forcing function of facility effects is described for discrepancies between results and the theoretical solution. Further work to eliminate these effects and add damping are proposed.
The Effects of Collisions on Plasma-Sheath Transition
Li, Yuzhi (Virginia Tech, 2023-05-05)
The plasma sheath is essential for understanding the plasma-material interaction (PMI) since it regulates the plasma particle and energy fluxes to the wall. The key concept in sheath theory is the Bohm criterion that gives the lower bound of the plasma exit flow speed, also known as the Bohm speed. Traditionally, the Bohm speed is evaluated in the asymptotic limit of an infinitely thin sheath and ignores the transport physics in the plasma-sheath transition problem. Whereas in practical applications, the sheath has a finite thickness and the transport in the neighborhood of the sheath entrance is complicated. The focus of this thesis is on performing Bohm speed analysis for different applications that are away from the asymptotic limits, with an emphasis on the critical role of transport physics on the Bohm speed formulation. The classical sheath problem with a wide range of Coulomb collisionality is revisited. Here, we derive an expression for the Bohm speed from a set of anisotropic plasma transport equations. The thermal force, temperature isotropization and heat flux enter into the eval- uation of the Bohm speed. Away from the asymptotic limit, it is shown that there exists a plasma-sheath transition region, rather than a single point at the sheath entrance. In the transition region, the quasineutrality is weakly perturbed and the Bohm speed is predicted for the entire transition region. By comparison with kinetic simulation results, the Bohm speed model in our work is shown to be accurate in the sheath transition region over a broad range of collisionality. The Bohm speed analysis developed above can be applied to plasma-sheath transition prob- lems with more complex transport physics, such as a high recycling divertor in a fusion reactor. In the high recycling regime, the plasma particles hitting on the divertor surface will be recycled through reflection or desorption and return to the plasma in the form of neutrals. The plasma will interact with the recycled neutrals through atomic collisions such as ionization, excitation, or ion charge-exchange collision, complicating the plasma transport in the transition layer. A new Bohm speed model is proposed to account for the effect of the anisotropic transport and atomic collisions in the transition layer. A first principle ki- netic code VPIC with the atomic collision package is used to investigate a 1D self-consistent slab plasma with a high recycling boundary for tungsten and carbon divertors. The results demonstrate the accuracy of the Bohm speed model in predicting the ion exit flow speed in the transition region, as well as the reduction of the Bohm speed due to the ion-neutral friction.
Effects of Solar Soft X-rays on Earth's Atmosphere
Samaddar, Srimoyee (Virginia Tech, 2023-02-06)
The soft x-rays (wavelengths less than 30 nm) emitted by the sun are responsible for the production of high energy photoelectrons in the D and E regions of the ionosphere, where they deposit most of their energy. The photoelectrons created by this process are the main drivers for dissociation of nitrogen ($N_2$) molecules in the altitude range below 200 km. The dissociation of $N_2$ is one of main mechanisms responsible for the production of nitric oxide (NO) at these altitudes. These processes are important to understand because NO plays a critical role in controlling the temperatures of various regions of Earth's atmosphere. In order to estimate the dissociation rate of $N_2$ we need its dissociation cross-sections. The dissociation cross-sections of $N_2$ due to inelastic collisions with electrons is primarily es- timated from the cross-sections of its excitation states (using predissociation factors) and dissociative ionization channels. Predissociation is the transition without emission of radi- ation from a stable excited state to an unstable excited state of a molecule that leads to dissociation. Unfortunately, the lack of cross-section data, particularly at high electron en- ergies and of higher excited states of N 2 and N 2 + , introduces uncertainty in the dissociation cross-section and subsequently the dissociation rate calculation, which leads to uncertainties in the NO production rate. We have updated a photoelectron model with thoroughly-revised electron impact cross- section data of all major species and experimentally determined predissociation factors. The dissociation rates of $N_2$ using this model are compared to the dissociation rates obtained using another existing (Solomon and Qian [2005]) model. A parameterized version of the updated dissociation rates are used in a one-dimensional global average thermospheric/ ionospheric model, ACE1D (Atmospheric Chemistry and Energetics), to obtain the updated production rates of NO. In the final chapter, we use the ACE1D model to show that the energies deposited by the solar soft x-rays in the lower thermosphere at altitudes between 100 -150 km affect the temperature of the Earth's thermosphere at altitudes well above 300 km. By turning off the input solar flux in the different wavelength bins of the model iteratively, we are able to demonstrate that the maximum change in exospheric temperature is due to changes in the soft solar x-ray bins. We also show, using the thermodynamic heat equation, that the molecular diffusion via non-thermal photoelectrons is the main source of heat transfer to the upper ionosphere/thermosphere. Moreover, these temperature changes and heating effects of the solar soft x-rays are comparable to that of the much stronger He II 30.4nm emission. Finally, we show that the uncertainties in the solar flux irradiance at these soft x-rays wavelengths result in corresponding uncertainties in the modeled exospheric temperature, and these uncertainties increase substantially with increased solar activity.
Forecasting Equatorial Ionospheric Convective Instability With ICON Satellite Measurements
Hysell, D. L.; Kirchman, A.; Harding, B. J.; Heelis, R. A.; England, Scott L. (American Geophysical Union, 2023-05)
Measurements from the Ionospheric Connections Explorer satellite (ICON) form the basis of direct numerical forecast simulations of plasma convective instability in the postsunset equatorial F region ionosphere. ICON data are selected and used to initialize and force the simulations and then to test the results one orbit later when the satellite revisits the same longitude. Data from the IVM plasma density and drifts instrument and the MIGHTI red-line thermospheric winds instrument are used to force the simulation. Data from IVM are also used to test for irregularities (electrically polarized plasma depletions). Fourteen datasets from late March 2022, were examined. The simulations correctly predicted the occurrence or non-occurrence of irregularities 12 times while producing one false positive and one false negative. This demonstrates that the important telltales of instability are present in the ICON state variables and that the important mechanisms for irregularity formation are captured by the simulation code. Possible refinements to the forecast strategy are discussed.
The Global-Scale Observations of the Limb and Disk (GOLD) Mission
Eastes, R. W.; McClintock, William E.; Burns, A. G.; Anderson, D. N.; Andersson, L.; Codrescu, M.; Correira, J. T.; Daniell, R. E.; England, Scott L.; Evans, J. S.; Harvey, J.; Krywonos, A.; Lumpe, J. D.; Richmond, A. D.; Rusch, D. W.; Siegmund, O. H.; Solomon, S. C.; Strickland, D. J.; Woods, T. N.; Aksnes, A.; Budzien, S. A.; Dymond, K. F.; Eparvier, F. G.; Martinis, C. R.; Oberheide, J. (2017-10)
The Earth's thermosphere and ionosphere constitute a dynamic system that varies daily in response to energy inputs from above and from below. This system can exhibit a significant response within an hour to changes in those inputs, as plasma and fluid processes compete to control its temperature, composition, and structure. Within this system, short wavelength solar radiation and charged particles from the magnetosphere deposit energy, and waves propagating from the lower atmosphere dissipate. Understanding the global-scale response of the thermosphere-ionosphere (T-I) system to these drivers is essential to advancing our physical understanding of coupling between the space environment and the Earth's atmosphere. Previous missions have successfully determined how the "climate" of the T-I system responds. The Global-scale Observations of the Limb and Disk (GOLD) mission will determine how the "weather" of the T-I responds, taking the next step in understanding the coupling between the space environment and the Earth's atmosphere. Operating in geostationary orbit, the GOLD imaging spectrograph will measure the Earth's emissions from 132 to 162 nm. These measurements will be used image two critical variables-thermospheric temperature and composition, near 160 km-on the dayside disk at half-hour time scales. At night they will be used to image the evolution of the low latitude ionosphere in the same regions that were observed earlier during the day. Due to the geostationary orbit being used the mission observes the same hemisphere repeatedly, allowing the unambiguous separation of spatial and temporal variability over the Americas.
GOLD Observations of the Merging of the Southern Crest of the Equatorial Ionization Anomaly and Aurora During the 10 and 11 May 2024 Mother's Day Super Geomagnetic Storm
Karan, Deepak Kumar; Martinis, Carlos R.; Daniell, Robert E.; Eastes, Richard W.; Wang, Wenbin; McClintock, William E.; Michell, Robert G.; England, Scott L. (Wiley, 2024-08-09)
Using NASA's Global‐scale Observations of the Limb and Disk (GOLD) imager, we report nightside ionospheric changes during the G5 super geomagnetic storm of 10 and 11 May 2024. Specifically, the nightside southern crest of the Equatorial Ionization Anomaly (EIA) was observed to merge with the aurora near the southern tip of South America. During the storm, the EIA southern crest was seen moving poleward as fast as 450 m/s. Furthermore, the aurora extended to mid‐latitudes reaching the southern tips of Africa and South America. The poleward shift of the equatorial ionospheric structure and equatorward motion of the aurora means there was no mid‐latitude ionosphere in this region. These observations offer unique insights into the ionospheric response to extreme geomagnetic disturbances, highlighting the complex interplay between solar activity and Earth's upper atmosphere.
GOLD Observations of the Thermospheric Response to the 10–12 May 2024 Gannon Superstorm
Evans, J.S.; Correira, J.; Lumpe, J.D.; Eastes, R.W.; Gan, Q.; Laskar, F.I.; Aryal, S.; Wang, W.; Burns, A.G.; Beland, S.; Cai, X.; Codrescu, M.; England, Scott L.; Greer, K.; Krywonos, A.; McClintock, W.E.; Plummer, T.; Veibell, V. (Wiley, 2024-08-16)
After days of intense solar activity, active region AR3664 launched seven CMEs toward Earth producing an extreme G5 geomagnetic storm commencing at 17:05 UT on 10 May 2024. The storm impacted power grids, disrupted precision navigational systems used by farming equipment, and generated aurora seen around the globe. The storm produced remarkable effects on composition, temperature, and dynamics in the Earth's thermosphere that were observed by NASA's Global‐scale Observations of the Limb and Disk (GOLD) mission and are reported here for the first time. We use synoptic disk images of ΣO/N₂ and neutral temperature (at ∼160 km) measured by GOLD to directly link dynamics resulting from the storm with dramatic changes in thermospheric composition and temperature. We observe a heretofore unseen spatial morphology simultaneously in ΣO/N₂, neutral temperature, and total electron content. Equator‐to‐pole temperature differences reach 400 K with high latitude peak neutral temperatures near 160 km exceeding 1400 K.
In Flight Performance of the Far Ultraviolet Instrument (FUV) on ICON
Frey, H. U.; Mende, S. B.; Meier, R. R.; Kamaci, U.; Urco, J. M.; Kamalabadi, F.; England, Scott L.; Immel, T. J. (Springer, 2023-04)
The NASA Ionospheric Connection Explorer (ICON) was launched in October 2019 and has been observing the upper atmosphere and ionosphere to understand the sources of their strong variability, to understand the energy and momentum transfer, and to determine how the solar wind and magnetospheric effects modify the internally-driven atmosphere-space system. The Far Ultraviolet Instrument (FUV) supports these goals by observing the ultraviolet airglow in day and night, determining the atmospheric and ionospheric composition and density distribution. Based on the combination of ground calibration and flight data, this paper describes how major instrument parameters have been verified or refined since launch, how science data are collected, and how the instrument has performed over the first 3 years of the science mission. It also provides a brief summary of science results obtained so far.
In-Flight Performance of the ICON EUV Spectrograph
Korpela, Eric J.; Sirk, Martin M.; Edelstein, Jerry; McPhate, Jason B.; Tuminello, Richard M.; Stephan, Andrew W.; England, Scott L.; Immel, Thomas J. (Springer, 2023-04)
We present in-flight performance measurements of the Ionospheric Connection Explorer EUV spectrometer, ICON EUV, a wide field (17 degrees x12 degrees) extreme ultraviolet (EUV) imaging spectrograph designed to observe the lower ionosphere at tangent altitudes between 100 and 500 km. The primary targets of the spectrometer, which has a spectral range of 54-88 nm, are the OII emission lines at 61.6 nmand 83.4 nm. In flight calibration and performance measurement has shown that the instrument has met all of the science performance requirements. We discuss the observed and expected changes in the instrument performance due to microchannel plate charge depletion, and how these changes were tracked over the first two years of flight. This paper shows raw data products from this instrument. A parallel paper (Stephan et al. in Space Sci. Rev. 218:63, 2022) in this volume discusses the use of these raw products to determine O+ density profiles versus altitude.
The Influence of Obliquely Propagating Monsoon Gravity Waves on the Polar Summer Mesosphere
Alexandre, David (Virginia Tech, 2021-07-01)
The deep convection from monsoons is known to be a major source of gravity waves in the Earth's summer troposphere. While propagating through the middle atmosphere, these waves can carry their momentum up to the mesosphere, following either a vertical or an oblique path. This upward and oblique propagation of gravity waves refers to the latitudinal propagation, away from their low-latitude tropospheric source and towards the polar summer mesosphere. Their dissipation in this atmospheric region plays an important role in the global dynamical structure of the middle atmosphere and yet, the oblique propagation of gravity waves is not included in the present global models. Understanding the influence of the obliquely propagating monsoon gravity waves on the polar summer mesosphere, as well as the hemispheric and seasonal variations of this phenomenon, can improve the gravity-wave parameterization schemes used in the global models. My dissertation relies upon the atmosphere theory and the gravity-wave observations, first, to perform an observational analysis of the oblique propagation of gravity waves in the summer hemisphere. In response to temperature anomalies in the winter northern stratosphere, the distribution of the gravity-wave pseudomomentum flux in the opposite summer mesosphere appeared to be altered. This in turn changes the gravity-wave oblique propagation and its influence on the temperature variations seen in the polar mesospheric clouds. After the development of a 4-D non-hydrostatic ray-tracing model for the simulation of the gravity-wave propagation, my dissertation explores the hemispheric and seasonal differences in the propagation and dissipation of more than 40,000 gravity waves from the low-latitude troposphere. These ray-tracing simulations show the southern hemisphere to be more conducive to both the vertical and the oblique propagation of tropospheric to mesospheric gravity waves. This analysis also highlighted a strong wave filtering at the northern tropopause where a significant number of gravity waves were vertically reflected before reaching the stratosphere.
Initial Observations by the GOLD Mission
Eastes, R. W.; McClintock, William E.; Burns, A. G.; Anderson, D. N.; Andersson, L.; Aryal, S.; Budzien, S. A.; Cai, X.; Codrescu, M.; Correira, J. T.; Daniell, R. E.; Dymond, K. F.; England, Scott L.; Eparvier, F. G.; Evans, J. S.; Foroosh, H.; Gan, Q.; Greer, K. R.; Karan, D. K.; Krywonos, A.; Laskar, F., I; Lumpe, J. D.; Martinis, C. R.; McPhate, J. B.; Oberheide, J.; Siegmund, O. H.; Solomon, S. C.; Veibel, V.; Woods, T. N. (2020-07)
The NASA Global-scale Observations of the Limb and Disk (GOLD) mission has flown an ultraviolet-imaging spectrograph on SES-14, a communications satellite in geostationary orbit at 47.5 degrees W longitude. That instrument observes the Earth's far ultraviolet (FUV) airglow at similar to 134-162 nm using two identical channels. The observations performed include limb scans, stellar occultations, and images of the sunlit and nightside disk from 6:10 to 00:40 universal time each day. Initial analyses reveal interesting and unexpected results as well as the potential for further studies of the Earth's thermosphere-ionosphere system and its responses to solar-geomagnetic forcing and atmospheric dynamics. Thermospheric composition ratios for major constituents, O and N-2, temperatures near 160 km, and exospheric temperatures are retrieved from the daytime observations. Molecular oxygen (O-2) densities are measured using stellar occultations. At night, emission from radiative recombination in the ionosphericFregion is used to quantify ionospheric density variations in the equatorial ionization anomaly (EIA). Regions of depletedFregion electron density are frequently evident, even during the current solar minimum. These depletions are caused by the "plasma fountain effect" and are associated with the instabilities, scintillations, or "spreadF" seen in other types of observations, and GOLD makes unique observations for their study. Plain Language Summary The NASA Global-scale Observations of the Limb and Disk (GOLD) mission has flown a dual-channel, ultraviolet-imaging spectrograph on SES-14, a communications satellite in geostationary orbit at 47.5 degrees W longitude. That instrument observes the Earth's far ultraviolet (FUV) airglow at similar to 134-162 nm. The observations performed include images of the Earth's sunlit and nightside disk, limb scans, and stellar occultations, from 6:10 to 00:40 universal time each day. Initial analyses reveal interesting and unexpected results as well as the potential for further studies of the Earth's thermosphere-ionosphere system and its responses to solar-geomagnetic forcing and atmospheric dynamics. Thermospheric temperatures and composition ratios for major constituents, O and N-2, near 160-km altitude and exospheric temperatures are retrieved from the daytime observations. Molecular oxygen (O-2) densities are measured using stellar occultations. At night, emission from radiative recombination in the ionospheric F region is used to quantify ionospheric density variations in the equatorial ionization anomaly (EIA). Regions of depleted F region electron density are frequently evident in the EIA, even during the current solar minimum.
Machine Learning and Data Fusion of Simulated Remote Sensing Data
Higgins, Erik Tracy (Virginia Tech, 2023-07-27)
Modeling and simulation tools are described and implemented in a single workflow to develop a means of simulating a ship wake followed by simulated synthetic aperture radar (SAR) and infra-red (IR) images of these ship wakes. A parametric study across several different ocean environments and simulated remote sensing platforms is conducted to generate a preliminary data set that is used for training and testing neural network--based ship wake detection models. Several different model architectures are trained and tested, which are able to provide a high degree of accuracy in classifying whether input SAR images contain a persistent ship wake. Several data fusion models are explored to understand how fusing data from different SAR bands may improve ship wake detection, with some combinations of neural networks and data fusion models achieving perfect or near-perfect performance. Finally, an outline for a future study into multi-physics data fusion across multiple sensor modalities is created and discussed.

Browsing by Author "England, Scott L."

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