A5073029119- Ionosphere and magnetosphere dynamics
- Solar and Space Plasma Dynamics
- Magnetic confinement fusion research
- Fluid Dynamics and Turbulent Flows
- Antenna Design and Optimization
- Astro and Planetary Science
- Antenna Design and Analysis
- Advanced Antenna and Metasurface Technologies
- Ultrasonics and Acoustic Wave Propagation
- Electromagnetic Simulation and Numerical Methods
- Non-Destructive Testing Techniques
- GNSS positioning and interference
- Geomagnetism and Paleomagnetism Studies
- Soil Moisture and Remote Sensing
- Geophysical Methods and Applications
- Precipitation Measurement and Analysis
- Space Satellite Systems and Control
- Radio Astronomy Observations and Technology
- Computational Fluid Dynamics and Aerodynamics
- Electromagnetic Compatibility and Measurements
- Numerical methods in inverse problems
- Electromagnetic Scattering and Analysis
- Geophysics and Sensor Technology
- Dust and Plasma Wave Phenomena
- Microwave Imaging and Scattering Analysis
Jet Propulsion Laboratory
2019-2024
Dartmouth College
2017-2019
University of Alaska Fairbanks
2017
Columbia University
2015-2017
United States Air Force Research Laboratory
1999-2010
Sensors (United States)
2007
Hanscom Air Force Base
1987-1999
Florida State University
1996
North Carolina State University
1996
Ames National Laboratory
1991-1993
This paper presents new results showing the application of polyomino-based subarrays to limited field view and wideband, wide-angle scanning. technology can reduce number phase controls in arrays used for sector coverage or time delay devices wideband radar communications, so cost space-based active arrays. We concentrate on application. Results are presented by comparing gain peak sidelobe irregular polyomino subarray-based with those rectangular subarrays. It is shown that using result a...
GNSS reflection measurements in the form of delay-Doppler maps (DDM) can be used to complement soil from SMAP Mission, which has a revisit rate too slow for some hydrological/meteorological studies. The standard approach, only considers peak value DDM, is subject significant amount uncertainty due fact that DDM not affected by moisture, but also complex topography, inundation, and overlying vegetation. We hypothesize information entire 2D could help decrease under various conditions....
Irregular polyomino-shaped subarrays are shown to provide a practical and effective means for introducing time delay into an array with phase steering. The elimination of quantisation lobes, resulting peak sidelobes suppressed more than 14 dB below the lobes rectangular subarrays, is demonstrated.
The optical properties of the transition-metal ions, ${\mathrm{Ni}}^{2+}$, ${\mathrm{Co}}^{2+}$, and ${\mathrm{Mn}}^{2+}$, in zirconium-barium-lanthanum-aluminum (ZBLA) fluoride glass are reported. Comparisons absorption spectra, luminescence lifetimes for these ions ZBLA ${\mathrm{MgF}}_{2}$ crystals have yielded following results. crystal field is much reduced compared with that ${\mathrm{MgF}}_{2}$. oscillator strengths transitions hosts almost an order magnitude larger than similar...
A method for the calculation of flow field a helicopter rotor blade in hover is presented. The approach uses finite volume solution three dimensional Euler equations near field. In solver velocity decomposed into two parts. One induced vortex wake extending below blade, found from free procedure. other part unknown additional blade. This eliminates numerical diffusion rolled up vorticity due to truncation error and artificial viscosity. Also, effects far are included limited computational...
An exact theory is developed for fields due to currents in the presence of an anisotropic slab. The anisotropy a type expected composite reinforced with unidirectional fiber and described by diagonal matrix Maxwell's equations. A Green's defined explicitly computed solutions equations point currents. reduces quadrature problems, frequency time domains, computing field produced inside outside slab arbitrary current sources. Steady-state AC sheets loops are considered, numerical results...
<h3>Abstract</h3> Radio frequency interference (RFI) in global navigation satellite system (GNSS) frequencies can endanger human life and safety by preventing the use of these signals for positioning, addition to degrading measurements science applications. Here, we data from Cyclone GNSS (CYGNSS) constellation map RFI 2017 2022, identify location several potential sources RFI, quantify duration transmission. Although our method detection only provide a rough approximation transmitter...
We examine electromagnetic pulse propagation in anomalously dispersive media, using the Debye model as an example. Short-pulse, long-pulse, short-time, and long-time approximations amplitude rate-of-decay estimates are derived with asymptotic methods. also study following problem: If we know only peak energy density of incident pulse, what can be said about propagated pulse? provide tight upper lower bounds for amplitude, which may useful controlling interference or damage produced media....
A model-based algorithm is developed for inverting eddy-current data and reconstructing flaws in advanced composite materials. The model incorporates an integral solution that built around the Green's function computed a companion paper. application of certain least-squares algorithms numerical method analytical continuation are described. Numerical experiments carried out simulated flaw graphite-epoxy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML"...
We report measurements of the turbulent evolution plasma density profile following fast injection lithium pellets into Levitated Dipole Experiment (LDX) [Boxer et al., Nat. Phys. 6, 207 (2010)]. As pellet passes through plasma, it provides a significant internal particle source and allows investigation evolution, relaxation, fluctuations. The total electron number within dipole torus increases by more than factor three, central five. During these large changes in density, shape is nearly...
Abstract Some existing auroral data products are insufficient for ionospheric simulation input on subkilometer spatial scales and high (second) time resolution near the boundaries of arc structures. Ideally, two‐dimensional maps relevant parameters over these small would provide models with constraining inputs. Available in situ have small‐scale features but only a 1‐D cut through structure. Ground‐based can 2‐D lower space than is required to accurately interpret structure an arc. This...
Global navigation satellite system (GNSS) signals are critically important for a wide range of commercial, military, and science applications. Recent studies have identified threats to the performance GNSS from both intended unintended sources radio frequency interference (RFI). Understanding distribution RFI nature that they emitting is critical determine mitigate their effects on measurements made by receivers. Terrestrial can be substantially detrimental received signals, affecting...
The problem of computing fields produced by currents in the presence unflawed layered media is reduced to quadrature. Each layer either has single-axis-type anisotropy or isotropic. Integral equations are derived for with flaws.
An exact computational algorithm that solves steady-state Maxwell equations for fields produced by electric currents in the presence of slabs with biaxial anisotropy is developed. Eigenmodes are computed explicitly and used to study unattenuated propagation transverse modes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
This paper presents data and a procedure for the use of irregular subarrays in planar wideband arrays. Using element-level phase shifters time delay at subarray ports, substitutes polyomino place conventional rectangular to eliminate quantization lobes. The focuses on following details design: choice size specified bandwidth, selection type, tradeoff between bandwidth peak sidelobe level. These items design are detailed arrays with 4- 8-element subarrays.
Measurement of ionospheric plasma is often performed by a single in situ device or remotely using cameras and radar. This article describes small, low-resource, deployed spacecraft used as part local, multipoint measurement network. A B-field aligned sounding rocket ejects four these spin-stabilized cross pattern. In this application, each carries two retarding potential analyzers which are to determine density, flow, ion temperature. An inertial unit light-emitting diode array the position...
Abstract The Rocket Experiment for Neutral Upwelling 2 (RENU2) rocket was launched on 13 December 2015 at 07:34 UT. payload transited the cusp region during a neutral upwelling event, supported by comprehensive set of onboard and ground‐based instrumentation. RENU2 data highlight two important processes. One is that proper understanding Poleward Moving Auroral Forms (PMAFs) requires treatment mimics quasiperiodic passage sequence PMAFs. As PMAF reaches flux tube, its physical consequences...
Abstract We use the Geospace Environment Model of Ion‐Neutral Interactions (GEMINI) to create three‐dimensional, time‐dependent simulations auroral ionospheric parameters in localized, several 100 km region surrounding arcs observed during a winter 2017 sounding rocket campaign, resolving three‐dimensional features fine‐scale (km) flow structures vicinity an arc. The calculations GEMINI allow (with sufficient driving data) current closure be investigated without idealizing assumptions...
Thermal ion retarding potential analyzers (RPAs) are used to measure in situ auroral ionospheric plasma parameters. This article analyzes data from a low-resource RPA order quantify the capability of sensor. The collects sigmoidal current-voltage (I-V) curve, which depends on non-linear combination Maxwellian parameters, so forward-modeling procedure is match best choice parameters for each I-V curve. First, used, given constraining information about flow moment, find scalar parameters-ion...
Passively sounding icy and rocky bodies in our solar system provides a way to observe the surface subsurface of these objects without need for costly transmitters. Jupiter's decametric radiation suitable source radio frequency signals on geological scales interest, but its spectral structure can introduce undesired artifacts. Recent studies have shown that Jovian bursts could be effectively applied as passive sounding. However, it has been noted properties bursts, measured with JUNO data,...
A method for computing the flow around a hovering helicopter rotor is presented. The solution procedure divided into two parts. first part finite volume of Euler equations near field blade. second free wake approach determining geometry and induced velocities. These parts are solved in coupled fashion. rolled-up vortex included computational domain through nonlinear perturbation technique. This eliminates numerical diffusion vorticity due to truncation error artificial viscosity without need...