Alexandria, VA, United States
Alexandria, VA, United States

Time filter

Source Type

Morrill J.S.,U.S. Navy | Floyd L.,Fm Technologies, Inc. | McMullin D.,Space Systems Research Corporation
Solar Physics | Year: 2014

Knowledge of solar spectral irradiance (SSI) is important in determining the impact of solar variability on climate. Observations of UV SSI have been made by the Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) on the Upper Atmosphere Research Satellite (UARS), the Solar-Stellar Irradiance Comparison Experiment (SOLSTICE), and the Solar Irradiance Monitor (SIM), both on the Solar Radiation and Climate Experiment (SORCE) satellite. Measurements by SUSIM and SORCE overlapped from 2003 to 2005. SUSIM and SORCE observations represent ∼ 20 years of absolute UV SSI. Unfortunately, significant differences exist between these two data sets. In particular, changes in SORCE UV SSI measurements, gathered at moderate and minimum solar activity, are a factor of two greater than the changes in SUSIM observations over the entire solar cycle. In addition, SORCE UV SSI have a substantially different relationship with the Mg ii index than did earlier UV SSI observations. Acceptance of these new SORCE results impose significant changes on our understanding of UV SSI variation. Alternatively, these differences in UV SSI observations indicate that some or all of these instruments have changes in instrument responsivity that are not fully accounted for by the current calibration. In this study, we compare UV SSI changes from SUSIM with those from SIM and SOLSTICE. The primary results are that (1) long-term observations by SUSIM and SORCE generally do not agree during the overlap period (2003 - 2005), (2) SUSIM observations during this overlap period are consistent with an SSI model based on Mg ii and early SUSIM SSI, and (3) when comparing the spectral irradiance for times of similar solar activity on either side of solar minimum, SUSIM observations show slight differences while the SORCE observations show variations that increase with time between spectra. Based on this work, we conclude that the instrument responsivity for SOLSTICE and SIM need to be reevaluated before these results can be used for climate-modeling studies. © 2014 Springer Science+Business Media Dordrecht.

Morrill J.S.,U.S. Navy | Floyd L.,Interferometrics | Ulrich R.,University of California at Los Angeles | Weaver S.,National Oceanic and Atmospheric Administration | McMullin D.,Space Systems Research Corporation
Solar Physics | Year: 2011

An empirical model of solar UV spectral irradiance has been developed that is based on observed spectral radiance measurements and full disk Ca ii K images. The Mg ii index is then calculated from the estimated spectra in a narrow wavelength range (180 Å) near the Mg ii doublet at 2800 Å. Our long term goal is to expand this wavelength range from 10 to 4000 Å in continuing studies based on spectral data covering this wavelength range (e. g. Skylab, UARS/SUSIM, TIMED/SEE, etc.). Our previous modeling effort produced spectra in this 180 Å range and the resulting Mg ii index values for the period from 1991 through 1995 and we have used observations during this time period to validate the model results. The current paper presents results from this model based on a 21-year portion of the recently digitized Ca ii K images from the Mt Wilson Observatory (MWO) film archive. Here we present details of the model, the required model modifications, and the resulting Mg ii index from 1961 through 1981. Since the NOAA Mg ii index did not begin until 1978, the present model results are compared to a Mg ii index estimated from the F10. 7 radio flux over this 21-year period. The NOAA Mg ii index, which is derived from measured UV spectra, is also included for comparison from late 1978 through 1981. © 2011 Springer Science+Business Media B.V.

Morrill J.S.,U.S. Navy | Floyd L.,Interferometrics | McMullin D.,Space Systems Research Corporation
Solar Physics | Year: 2011

As part of a program to estimate the solar spectrum back to the early twentieth century, we have generated fits to UV spectral irradiance measurements from 1 - 410 nm. The longer wavelength spectra (150 - 410 nm) were fit as a function of two solar activity proxies, the Mg ii core-to-wing ratio, or Mg ii index, and the total Ca ii K disk activity derived from ground based observations. Irradiance spectra at shorter wavelengths (1 - 150 nm) where used to generate fits to the Mg ii core-to-wing ratio alone. Two sets of spectra were used in these fitting procedures. The fits at longer wavelengths (150 to 410 nm) were derived from the high-resolution spectra taken by the Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) on the Upper Atmospheric Research Satellite (UARS). Spectra measured by the Solar EUV Experiment (SEE) instrument on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite were used for the fits at wavelengths from 1 to 150 nm. To generate fits between solar irradiance and solar proxies, this study uses the above irradiance data, the NOAA composite Mg ii index, and daily Ca ii K disk activity determined from images measured by Big Bear Solar Observatory (BBSO). In addition to the fitting coefficients between irradiance and solar proxies, other results from this study include an estimated relationship between the fraction of the disk with enhanced Ca ii K activity and the Mg ii index, an upper bound of the average solar UV spectral irradiance during periods where the solar disk contains only regions of the quiet Sun, as was believed to be present during the Maunder Minimum, as well as results indicating that slightly more than 60% of the total solar irradiance (TSI) variability occurs between 150 and 400 nm. © 2011 US Government.

Evans J.S.,Computational Physics, Inc. | Strickland D.J.,Computational Physics, Inc. | Woo W.K.,Computational Physics, Inc. | McMullin D.R.,Space Systems Research Corporation | And 5 more authors.
Solar Physics | Year: 2010

NOAA's GOES-13 satellite, launched in May 2006, includes a new solar sensor, called EUVS (Extreme UltraViolet Sensor), that measures energy fluxes in five broad-band spectral channels that span the region from 1 to 130 nm. Here, we report on measurements made during the mission's six-month post-launch test (PLT) period which provided nearly continuous observations from August through November 2006 and the recording of an X9 flare that occurred on 5 December 2006. In this paper, we present a calibration model for the GOES EUVS that incorporates the effects of pointing offsets, cross-disk radiance variability (radiance refers to partial-disk emission), and changes to assumed spectral shapes. Appendices are included that report on the sensitivity to these effects. The main body of the paper gives a description of the model and data recorded during the PLT period. Comparisons are made with time-coincident measurements from TIMED/SEE (Version 10.02), SOHO/SEM, and SORCE/ SOLSTICE for the time period August-November. Comparisons are made with SORCE/XPS for the 5 December flare. In general, there is agreement among the data sets within expected measurement uncertainties. There will be a series of EUVSs extending into the next generation of GOES (starting with GOES-13). The initial performance of GOES-13 EUVS, including 5-channel measurements approximately every 11 s on a nearly continuous basis, suggests that the EUVS series will play a key role over the next many years in monitoring solar EUV variability. © 2010 The Author(s).

Katushkina O.A.,Russian Academy of Sciences | Izmodenov V.V.,Russian Academy of Sciences | Wood B.E.,U.S. Navy | McMullin D.R.,Space Systems Research Corporation
Astrophysical Journal | Year: 2014

Recent analysis of the interstellar helium fluxes measured in 2009-2010 at Earth's orbit by the Interstellar Boundary Explorer (IBEX) has suggested that the interstellar velocity (both direction and magnitude) is inconsistent with that derived previously from Ulysses/GAS observations made in the period from 1990 to 2002 at 1.5-5.5 AU from the Sun. Both results are model dependent, and models that were used in the analyses are different. In this paper, we perform an analysis of the Ulysses/GAS and IBEX-Lo data using our state-of-the-art three-dimensional time-dependent kinetic model of interstellar atoms in the heliosphere. For the first time, we analyze Ulysses/GAS data from year 2007, the closest available Ulysses/GAS observations in time to the IBEX observations. We show that the interstellar velocity derived from the Ulysses 2007 data is consistent with previous Ulysses results and does not agree with the velocity derived from IBEX. This conclusion is very robust since, as is shown in the paper, it does not depend on the ionization rates adopted in theoretical models. We conclude that Ulysses data are not consistent with the new local interstellar medium (LISM) velocity vector from IBEX. In contrast, IBEX data, in principle, could be explained with the LISM velocity vector derived from the Ulysses data. This is possible for the models where the interstellar temperature increased from 6300 K to 9000 K. There is a need to perform further studies of possible reasons for the broadening of the helium signal core measured by IBEX, which could be an instrumental effect or could be due to unconsidered physical processes. © 2014. The American Astronomical Society. All rights reserved.

Nicholas A.C.,U.S. Navy | Herrero F.A.,Space Systems Research Corporation | Stephan A.W.,U.S. Navy | Finne T.,U.S. Navy
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

The Winds-Ions-Neutral Composition Suite (WINCS) instrument, also known as the Small Wind and Temperature Spectrometer (SWATS), was designed and developed jointly by the Naval Research Laboratory (NRL) and NASA/Goddard Space Flight Center (GSFC) for ionosphere-thermosphere investigations in orbit between 120 and 550 km altitude. The WINCS instrument houses four spectrometers in a single package with size, weight, and power compatible with a CubeSat. These spectrometers provide the following measurements: neutral winds, neutral temperature, neutral density, neutral composition, ion drifts, ion temperature, ion density and ion composition. The instrument is currently operating on the International Space Station and on the STP-Sat3 spacecraft. Data from the Ion-Drift Temperature-Spectrometer (IDTS) are used to compute the ion drift, temperature, and density in the presence of large changes in spacecraft potential. A summary is given of future flight manifests. © 2015 SPIE.

Woods T.N.,University of Colorado at Boulder | Eparvier F.G.,University of Colorado at Boulder | Hock R.,University of Colorado at Boulder | Jones A.R.,University of Colorado at Boulder | And 14 more authors.
Solar Physics | Year: 2012

The highly variable solar extreme ultraviolet (EUV) radiation is the major energy input to the Earth's upper atmosphere, strongly impacting the geospace environment, affecting satellite operations, communications, and navigation. The Extreme ultraviolet Variability Experiment (EVE) onboard the NASA Solar Dynamics Observatory (SDO) will measure the solar EUV irradiance from 0.1 to 105 nm with unprecedented spectral resolution (0.1 nm), temporal cadence (ten seconds), and accuracy (20%). EVE includes several irradiance instruments: The Multiple EUV Grating Spectrographs (MEGS)-A is a grazing-incidence spectrograph that measures the solar EUV irradiance in the 5 to 37 nm range with 0.1-nm resolution, and the MEGS-B is a normal-incidence, dual-pass spectrograph that measures the solar EUV irradiance in the 35 to 105 nm range with 0.1-nm resolution. To provide MEGS in-flight calibration, the EUV SpectroPhotometer (ESP) measures the solar EUV irradiance in broadbands between 0.1 and 39 nm, and a MEGS-Photometer measures the Sun's bright hydrogen emission at 121.6 nm. The EVE data products include a near real-time space-weather product (Level 0C), which provides the solar EUV irradiance in specific bands and also spectra in 0.1-nm intervals with a cadence of one minute and with a time delay of less than 15 minutes. The EVE higher-level products are Level 2 with the solar EUV irradiance at higher time cadence (0.25 seconds for photometers and ten seconds for spectrographs) and Level 3 with averages of the solar irradiance over a day and over each one-hour period. The EVE team also plans to advance existing models of solar EUV irradiance and to operationally use the EVE measurements in models of Earth's ionosphere and thermosphere. Improved understanding of the evolution of solar flares and extending the various models to incorporate solar flare events are high priorities for the EVE team. © 2010 The Author(s).

Sultana M.,NASA | Herrero F.,Space Systems Research Corporation | Khazanov G.,NASA
Radiation Effects and Defects in Solids | Year: 2013

Graphene is a single layer of carbon atoms that offer a unique set of advantages as a chemical sensor due to a number of its inherent properties. Graphene has been explored as a gas sensor for a variety of gases, and molecular sensitivity has been demonstrated by measuring the change in electrical properties due to the adsorption of target species (Schedin, F.; Geim, A.K.; Morozov, S.V.; Hill, E.W.; Blake, P.; Katsnelson, M.I.; Novoselov, K.S. Nat. Mater 2007, 6, 652-655. doi:10.1038/nmat1967). In this paper, we discuss the development of an array of chemical sensors based on graphene and its relevance to plasma physics due to its sensitivity to radical species such as O+, H+ and the corresponding neutrals. We briefly discuss the great impact such sensors will have on a number of heliophysics applications such as ground-based manifestations of space weather. © 2013 Taylor & Francis.

Herrero F.A.,NASA | Herrero F.A.,Space Systems Research Corporation | Khazanov G.V.,NASA
Radiation Effects and Defects in Solids | Year: 2013

A charged-particle spectrometer is described that uses a configuration of the 30° parallel plate analyzer that differs from the previous one in that the entrance slit sits at the base plate while the exit slit is, as before, displaced to a point beneath the base plate. This approach preserves the second-order focusing previously found, yielding energy resolution of 0.01-0.3 eV for electrons in the energy range 1-30 eV. This is sufficient to address two identified problems in ionospheric electron energy distributions. In addition, the analyzer provides focusing of electron energies along a flat plane to operate as an energy spectrograph with a geometric factor of 10-3 cm2-sr at an energy resolution Δ K/K=0.01; the performance required for very high resolution photoelectron spectroscopy in the ionospheric plasma. © 2013 Taylor & Francis.

Agency: National Aeronautics and Space Administration | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 124.72K | Year: 2013

A new detector evaluation method (DEM) is proposed to determine the response of graphene detectors to low fluxes of photons, neutral atoms/molecules, and ions in the space environment of high to ultra-high vacuum. The method, aimed mainly at evaluation for space applications of new graphene detectors, is also applicable to other detectors operating in non-space environments. DEM will test graphene response to very low fluxes of atoms and molecules, ions, and photons; if sensitive to extremely low fluxes of a few 100/s, the timing of pulses produced by bunched events may open up an entirely new avenue to time-of-flight mass spectrometry. Closely coordinating with the NASA GSFC Detector Systems Branch, DEM will characterize the detector response to enable low-cost demonstrations of ionosphere-thermosphere investigations in low-Earth-orbit in CubeSats and sounding rockets. Space-borne measurements require knowledge of the response to the three kinds of particles: photons, ions, and neutrals, to properly design experiments. DEM controls vacuum pressure at the detector and can validate the application of these new detectors to a new series of mass spectrometers that can operate over a broad range of vacuum pressures (0.1 milliTorr and lower) because of their small size?DEM will add value to cost effective NASA balloon, sounding rocket, and satellite investigations.

Loading Space Systems Research Corporation collaborators
Loading Space Systems Research Corporation collaborators