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The GOLD mission of opportunity will fly a far ultraviolet imaging spectrograph in geostationary (GEO) orbit as a hosted payload. The GOLD imager, now being integrated onto the SES-14 satellite, is scheduled for launch in late 2017. SES-14, a commercial communications satellite, will be stationed over eastern South America at 47.5° west longitude. The GOLD imager has two identical channels. Each channel can scan the full disk at a 30 minute cadence, making spectral images of Earth’s UV emission from 132 to 162 nm, as well as make a measurement on the Earth’s limb. Remote sensing techniques that have been proven on previous Low Earth Orbit (LEO) missions will be used to derive fundamental parameters for the neutral and ionized space environment. Parameters that will be derived include composition (O/N2 ratio) and temperature of the neutral atmosphere on the dayside disk. On the nightside, peak electron densities will be obtained in the low latitude ionosphere. Similar imaging of atmospheric composition from LEO, at only a daily cadence for revisiting locations, has already provided many new insights into the behavior of Earth’s Thermosphere-Ionosphere (T-I) system. From geostationary orbit, GOLD can repeatedly image the same geographic locations over most of the hemisphere at a cadence comparable to that of the T-I system (order of an hour). Such time resolution and spatial coverage will allow the mission to track the changes due to geomagnetic storms, variations in solar extreme ultraviolet radiation, and forcing from the lower atmosphere. In addition to providing a new perspective by being able to repeatedly remotely sense the same hemisphere at a high cadence, GOLD’s simultaneous measurements of not only composition but also temperatures across the disk will provide a valuable, new parameter for understanding of how the T-I system responds to forcing from the Sun and the lower atmosphere.
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Global-scale Observations of the Limb and Disk (GOLD) Mission – Ultraviolet Remote Sensing of Earth’s Space Environment
R.W. Eastes, M. Codrescu, W.E. McClintock, A.G. Burns, S.C. Solomon, D.N. Anderson, L. Andersson, R.E. Daniell, S.L. England, J.S. Evans, J.E. Harvey, A. Krywonos, J.D. Lumpe, A.D. Richmond, D.W. Rusch, O. Siegmund, T.N. Woods, A. Aksnes, S.A.Budzien, K.F. Dymond, F.G. Eparvier, C.R. MarLnis, J. Oberheide, and H. Foroosh
GOLD Science Data Processing
Table 1: GOLD Level 2 data products
GOLD Data Products
Thermospheric Temperature O/N2 Column Density Ratio & QEUV
Overview
ALGORITHM The retrieval algorithm is an extension of those used previously with HITS data. An effective temperature at ~160 km is retrieved by fitting the observed rotational structure of the N2 LBH bands, using an optimal estimation routine driven by a forward model that includes the instrument lineshape, N2 and temperature variation along the slant-path line of sight, and photoabsorption by O2.
1440 1450 1460 1470 1480 1490 1500 1510 1520 1530 1540 15500
10
20
30
40
50
60
70
80
90
100
110
Wavelength (Å)
Cou
nts/
Sam
ple
N2 LBH with NI 1493 removed
Simulated DataFit
1460 1465 1470 1475 14800
50
100
150
200
250
300
350
400
Wavelength (Å)
Rel
ativ
e B
right
ness
T=400KT=600KT=1000K
(5,4)
(1,1)
REFERENCES Aksnes, A., R. Eastes, S. Budzien, and K. Dymond (2006), Neutral temperatures in the lower thermosphere from N2 Lyman-Birge-Hopfield (LBH) band profiles, Geophys. Res. Lett., 33, L15103, doi:10.1029/2006GL026255. Krywonos, A., D. J. Murray, R. W. Eastes, A. Aksnes, S. A. Budzien, and R. E. Daniell (2012), Remote sensing of neutral temperatures in the Earth's thermosphere using the Lyman-Birge-Hopfield bands of N2: Comparisons with satellite drag data, J. Geophys. Res., 117, A09311, doi:10.1029/2011JA017226.
Dayside disk measurement Spatial Resolution: 250 x 250 km2
Cadence: 60 minutes Precision: 55 K
Dayside disk measurement Spatial Resolution: 250 x 250 km2
Cadence: 30 minutes Precision: 10%
REFERENCES Strickland, D. J., J. S. Evans, and L. J. Paxton, Satellite remote sensing of thermospheric O/N2 and solar EUV: 1. Theory, J. Geophys. Res., 100, 12,217, 1995. Strickland, D. J., et al., Quiet-time seasonal behavior of the thermosphere seen in the far ultraviolet dayglow, J. Geophys. Res., 109, A01302, doi:10.1029/2003JA010220, 2004. Strickland, D. J., et al., Constraining and validating Oct/Nov 2003 X-class EUV flare enhancements with observations of FUV dayglow and E-region electron densities, J. Geophys. Res., 112, A06313, doi:10.1029/2006JA012074, 2007.
ALGORITHMS The disk O/N2 retrieval algorithm has been developed for use with GUVI and SSUSI images, and will take advantage of GOLD’s ability to transmit the full spectrum to better eliminate some atomic emission lines that contaminate the N2 LBH bands. This algorithm has been extensively documented and applied. O/N2 column density is derived from the ratio of measured OI 135.6 nm and N2 LBH band brightness. The AURIC model is used to derive this relationship as a function of solar zenith angle and create the look-up tables (LUT) used by the algoritm. The QEUV (solar irradiance proxy) product is also produced via a LUT approach, and depends on the observed OI 135.6 nm brightness, the solar zenith angle, and the derived O/N2 ratio.
O2 Density Profile
ALGORITHM O2 is derived from measurements of stellar occultation in the Shumann Runge continuum. The retrieval algorithm is based on POAM-heritage solar occultation algorithms. It has been previously used to retrieve thermospheric O2 profiles from SUSIM/UARS solar occultation measurements and SOLSTICE/SORCE stellar occultation measurements. Retrievals will utilize several 1-nm spectral channels between 132 and 162 nm, using the spectral dependence of the O2 absorption cross-section to maximize the O2 retrieval altitude range.
REFERENCES Lumpe, J. D., L. E. Floyd, L. C. Herring, S. T. Gibson, and B. R. Lewis (2007), Measurements of thermospheric molecular oxygen from the Solar Ultraviolet Spectral Irradiance Monitor, J. Geophys. Res., 112, D16308, doi:10.1029/2006JD008076. Lumpe, J. D., L. Floyd, M. Snow, and T. Woods, “Thermospheric Remote Sensing by Occultation: Comparison of SUSIM and SOLSTICE O2 Measurements”, Presented at the Fall 2006 AGU meeting, San Francisco, CA, December 11-15 2006. Lumpe, J. D., R. M. Bevilacqua, K. W. Hoppel, & C. E. Randall (2002), POAM III retrieval algorithm and error analysis, J. Geophys. Res., 107(D21), 4575, doi:10.1029/2002JD002137.
Limb measurement – day & night Frequency: 10-12 occultations per day
Local times from 0 – 24 hrs Latitudes to ±60 degrees; 2 fixed longitudes
Altitude Range: 130 – 250 km Accuracy & Precision: ≤ 10 % Vertical Resolution: ≤ 10 km
−40 −20 0 20 40120140160180200220240260
MeanStd Dev
Nighttime
high SNRmid SNRlow SNR
−40 −20 0 20 40120140160180200220240260
MeanStd Dev
Daytime
Alti
tud
e (
km)
O/N2 Error (%)O2 Error (%)
Ionospheric Bubbles (Level 3 Product)
REFERENCES Park, S. H., S. L. England, T. J. Immel, H. U. Frey, and S. B. Mende (2007), A method for determining the drift velocity of plasma depletions in the equatorial ionosphere using far-ultraviolet spacecraft observations, J. Geophys. Res., 112, A11314, doi:10.1029/2007JA012327. England, S. L., and T. J. Immel (2012), An empirical model of the drift velocity of equatorial plasma depletions, J. Geophys. Res., 117, A12308, doi:10.1029/2012JA018091. Guiping Liu, Scott L. England, Harald U. Frey, Thomas J. Immel, Chin S. Lin, Edgardo E. Pacheco, Kathrin Hausler, Eelco Doornbos, Comparison of drift velocities of nighttime equatorial plasma depletions with ambient plasma drifts and thermospheric neutral winds, J. Geophys. Res., in press.
ALGORITHM The detection of bubble locations and drifts is based on the algorithm developed for IMAGE-FUV [Park et al., 2007]. This algorithm uses a simple image-processing system to detect discrete regions of reduced O+ recombination airglow. Coherence of these reduced regions over a range of both time and magnetic latitude is used as the detection criteria. The existing algorithm will be reformulated for GOLD’s imaging resolution and temporal cadence. However, the most difficult part of this algorithm – that of mapping the emissions to geographic locations – which was challenging for IMAGE-FUV, is trivial for GOLD, given its geostationary viewing.
Incident Radiance 50 x 200 km2 binning COUNTS/WITH NOISE 100 x 100 km2 binning
Night side disk measurement Local time: 19 – 22 hrs Cadence: 20 min, single arc Resolution: TBD
Simulated LBH spectrum with fit. Sensitivity of the (1,1) and (5,4) LBH bands to temperature. The temperature dependence of the band is the basis of the temperature retrievals.
Global O/N2 response to Nov 20, 2003 storm. TIMED/GUVI data. Comparison of pre-flare and flare GUVI nadir data, QEUV, and O/N2
versus latitude on two days: 28 October (left panels) and 4 November (right panels).
O2 density retrieval accuracy (blue lines) and precision (red lines).
Occultation time/latitude sampling at equinox and solstice. Each star occults at a constant latitude. There are two points for each star, corresponding to star rise (SR, blue) and star set (SS, green) occultations.
Simulated GOLD images at 1820 satellite local time..
Exospheric Temperature Day side limb measurement
Latitudes: 10oS – 10oN Cadence: 30 min Precision: 40 K
ALGORITHM Exospheric temperatures (Texo) will be derived from the limb scan data by fitting the shape of the LBH radiance profile above 200 km. Texo has a direct relationship to this topside slope, which is also weakly dependent on O/N2 composition, and on the photoelectron model used. The GOLD algorithm will rely on CPI’s AURIC airglow model. A similar approach has been used to analyze data from TIMED/GUVI, Cassini/UVIS and MAVEN/IUVS.
Simulation of exospheric temperature retrieval from N2 LBH bands using model fits to the topside profile. Symbols: simulated data including Poisson noise, slit function, and jitter. Red dotted line: initial guess using model scaled to the simulated airglow peak intensity. Black dashed line: final fit after iterative adjustment of exospheric temperature.
Peak Electron Density Night side disk measurement - Equatorial anomaly region Cadence: 20 min Local time: 19 – 22 hrs Resolution: 200 x 200 km2
ALGORITHM The peak electron density (Nmax) will be deduced from the OI 135.6 nm nightglow emission. This method has been used successfully with TIMED/GUVI. The 135.6 nm volume emission rate is assumed to be proportional to the square of the electron density. Although the observed radiance is, by definition, integrated over the entire column of emitters, it is most sensitive to the peak electron density and thus Nmax is derived directly from the square root of the radiance. Primary assumptions made: neglect multiple scattering and ion-ion mutual neutralization; assume Ne = NO+.
REFERENCES Chandra, S., E. I. Reed, R. R. Meier, C. B. Opal, and G. T. Hicks (1975), Remote Sensing of the Ionospheric F Layer by Use of OI 6300-Å and OI 1356-Å Observations, J. Geophys. Res., 80, 2327-2332. Rajesh, P. K., J. Y. Liu, M. L. Hsu, C. H. Lin, K. I. Oyama, and L. J. Paxton (2011), Ionospheric electron content and NmF2 from nighttime OI 135.6 nm intensity, J. Geophys. Res., 116, A02313, doi:10.1029/2010JA015686. Tinsley, B. A., and J. A. Bittencourt (1975), Determination of F Region Height and Peak Electron Density at Night Using Airglow Emissions From Atomic Oxygen, J. Geophys. Res., 80, 2333-2337.
GOLD Science Data Levels. Levels 0 & 1A will be processed at the SOC and transferred to the SDC for processing of all higher-level data products.
GOLD ground data system: data received from the mission ground station is centralized through the Science Operations Center (SOC), and transformed into various levels of data products at the Science Data Center (SDC) for delivery to users.
INSTITUTIONAL ROLES AND RESPONSIBILITIES SES Government Solutions (SES-GS) SES-GS provides mission and instrument control, the ground station to receive the GOLD telemetry data, operation of the ground station, and transfer of telemetry data to the SOC. University of Colorado, Laboratory for Atmospheric and Space Physics (CU/LASP) LASP will house the SOC and will be responsible for constructing command sequences for the instrument, receiving the telemetry from SES-GS, monitoring the instrument status, development of Level 1 algorithms, production of Level 1A data products and archiving housekeeping data. University of Central Florida (UCF) UCF will house the GOLD SDC and maintain overall responsibility for accomplishing the GOLD Mission of Opportunity, which includes developing mission policies and procedures for data ingestion, processing, validation, and distribution. Computational Physics, Inc. (CPI) CPI is responsible for overall management of the development, implementation, and validation of the science algorithms and data processing pipeline to generate Level 2 science data products.
Raw data (CCSDS packets) received at the SOC. Level 0
• Data separated by observation type – DAY, NIT, LIM & OCC. • Data is binned and mapped in GOLD coordinates, with geolocation information added. • Temporal binning applied (Disk/Limb only). • Image data cube in counts.
• Additional spatial and spectral binning applied. • Data saved in both counts and brightness (calibrated) units. Backgrounds removed and
included in data file. • Separate file cadence for each OBS_TYP: one file for each disk scan, limb scan and
occultation event.
• Primary scientific data products. • Retrieval algorithms are applied to L1C brightness data to generate geophysical parameters. • Separate daily files produced for each of 6 data products (see Table 1).
• Data products requiring higher-order modeling or averaging. • Temporal averages and time series of Level 2 data products.
Level 2
Level 1B
Level 1C
Geolocation Step
Calibration Step
Retrieval Step
Level 3
Level 1A • Time-tagged stream of photon events - detector coordinates and pulse heights. • Telemetry data numbers are converted to engineering units. Minimal processing.
Level 1D
Publ
ic R
elea
se
SES GOLD Ground Station (GGS)
High-rate telemetry
SES Satellite Control Center (SCC)
S/C Ops & Instrument Commanding
LASP Science Operations Center
(SOC) Instrument monitor, ops,
plan, command, L0, L1A generation
Science Data Users GOLD Co-Is, Science
Community, SPDF
GOLD Science Centers (GSC)
SES
UCF Science Data Center (SDC)
L1B-D, L2 & L3 product generation
L0 – L3 Archive
Data Latency
Table 2. Estimated Science Data Delivery Capability (after start of routine processing)
Data Spacecraft to SOC
SOC to SDC
SDC to GOLD Team
SDC to Public
SDC to SPDF
Raw Telemetry Real-time N/A N/A N/A N/A
Level 0 N/A < 1 hour N/A N/A 1 month
Level 1A N/A < 1 hour < 1 hour N/A 1 month
Level 1B N/A N/A < 3 hours N/A 1 month
Level 1C N/A N/A < 4 hours 2 days 1 month
Level 1D N/A N/A < 4 hours < 4 hours 1 month
Level 2 N/A N/A < 4 hours 2 days 1 month
Level 3 N/A N/A Varies Varies Varies
All times are relative to receipt of GOLD data at the GGS
The boxes below and to the right provide a summary of GOLD data products including a brief algorithm description, retrieval/data product heritage, references and plots illustrating the technique and results.
Ø GOLD imager now being integrated onto SES-14 spacecraft Ø Launch planed for last quarter of 2017 (this year) Ø Transfer to geostationary orbit by electric propulsion Ø SES-14 orbit located at 47.5 degrees West longitude Ø Observations expected to begin in second quarter of 2018
Mission Status
• Quicklook images from L1C data.
3/21
-50
0
50
6/21
-50
0
50
9/21
0 5 10 15 20
-50
0
50
12/21
0 5 10 15 20
-50
0
50
GOLD Occultation Sampling - All OCCs
Satellite Local Time (hr)
Latit
ude
(deg
)
Star Rise
Star Set
Single Star
Integration of GOLD imager (upper left, with protective covers) onto the SES-14 spacecraft began in early April when the instrument was mounted onto the spacecraft.
Data Product Description [units]
Cadence Spatial coverage/resolution
O/N2 Neutral composition. Ratio of O to N2 vertical column density.
[dimensionless]
30 minutes
Retrievals over the sunlit region globe at 250 x 250 km2 resolution (nadir).
Tneut
Thermospheric neutral temperature at reference altitude Zref ~150 km.
[K]
60 minutes
Retrievals over the sunlit region at 250x250 km2 resolution (nadir).
QEUV Solar EUV flux proxy.
[mW/m2]
1 minute
No spatial dependence. Average four L1C columns to capture temporal dependence.
Texo Neutral exospheric temperature.
[K]
30 minutes
2 Longitudes: (E/W limbs) Latitudes: 10oS–10oN Retrievals on sunlit limb only.
O2
Molecular oxygen number density profile.
[mol/cm3]
~12 scans per day at irregular sampling.
2 Longitudes: (E/W limbs) Latitudes: 60oS–60oN Altitudes: 130-250 km. SLT: 03-21 hrs.
Nmax
Peak electron density.
[electrons/cm3]
Minimum of one arc every
20 minutes.
Coverage in the nightside equatorial anomaly region between 19 and 22 ground local time. 200x200 km2 resolution (nadir).
