Post on 27-Jul-2020
Ionosphere ObservabilityUsing GNSS and LEO
Platforms
Brian BreitschAdvisor: Dr. Jade Morton
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Motivate ionosphere TEC observationsPast work in ionosphere observabilityObservation volume
Ground receiversLEO radio occultations (RO)Joint ground and LEO overhead/ROLEO beacons
Data affects in simulated localized imaging
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Image credit: NASA/J. Grobowsky 2014
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Image credit:
NASA
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T EC = N (x)dx∫ rxsat
e
observed by multi-frequency GNSS
LEO reflection
LEO occultation
LEO beacon
ground GNSS
LEO overhead
Ionosphere TEC
low Earth-orbiting(LEO)
Global NavigationSatellite System
(GNSS)
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2D and 3D ionospheremaps of electrondensity from TECmeasurements
Image Credit: "Multi-satellite ionosphere-plasmasphereelectron density reconstruction", GFZ Potsdam
Previous Work
climatological andlarge-scale
Wang Yang
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"Observing System Simulation Experiment
Study on Imaging the Ionosphere by
Assimilating Observations From Ground
GNSS, LEO-Based Radio Occultation and
Ocean Reflection, and Cross Link"
PreviousWork
Xinan Yue et. al. 2013
LEO occultationslargely contribute toglobal-scale modelsdue to lack of groundRX over oceans
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GNSS Ground ReceiversGPS Lab
High-rate GNSSdata collection
network
IGSStation Map
GNSS network data available
from many sources: IGS,
CORS, ARGN, etc.
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Ground RXObservations
GNSS sky plots
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Ground RXObservations 700 km 400 km 100 km
60°
30°
0°
GNSS signalionosphere piercingpoints for groundreceiver atlow/mid/high latitude5° elevation mask
IPP
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LEO Receiver Observations
orbital altitude: between 500-800 kmorbital inclination: 24° or 72°
occultation
tangent point (TP)
e.g. COSMIC/COSMIC-2
use POD antennahighly localized to LEOsatellite
use occultation antennastraverse large ionosphere volume
Radio Occultations (RO)
Overhead Obs.
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LEO Occultations 90-day scatter of COSMIC-GPS
occultation tangent points
top coords. bottom coords.
tangent point altitude histogram
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LEO Occultations
90-day histogram ofCOSMIC-GPS occultationtangent point azimuths
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Geometry
common observation volume
RO tangent point
Ground/LEO Common Volume
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3D Line-Segment Intersection
common-volume point-of-interest
midpoint b/w points ofclosest approachGNSS rays <100 km apart
"the points of closestapproach between two line
segments"
*must handle special case where
point of closest approch is on
segment endpoint.
Ground/LEO Common Volume
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Ground/LEOCommonVolume
60°
40°
20°
0°
6-satellite constellation
750 km altitude
24° inclination
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Ground/LEOCommonVolume
60°
40°
20°
0°
6-satellite constellation
750 km altitude
72° inclination
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Ground/LEOCommonVolume
6-satellite constellation
750 km altitude
24° and 72° inclination
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LEO BeaconObservations
LEO constellationground track coverage72° incl.
LEO beacon IPP@ 150 km and 20° elev. if we had beacon RX at every IGS station
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Simulated Effects onLocalized Imaging
regional IGS network inEuropelatitudes
43°-53° @ 0.25° sep.longitudes
6°-15° @ 3° sep.altitudes
100-980 km @ 20 kmattempt to reconstruct IRIimage with depletionfeature from uniformdensity starting image
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Simulated Effects on
Localized Imagingground
LEO RO/overhead
ground
LEO beacon
LEO RO/overhead
ground
100 km
1000 km
53°43°
no regularization used in order to emphasize affects of different
data 21
Future Work
Low elevation groundGNSS esspeciallyimportant at low altitudeuse 3-frequency GNSSmeasurements to addresslow-elevation TECestimation
20° el.
mask
5° el.
mask
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Conclusions
Poleward deficit of GNSS satellites causes gap ininformation from ground receiversOccurrence of ground and LEO GNSS observations incommon volume heavily depends upon LEO constellationorbital inclinationOverhead and RO LEO observations aid in topsideionosphere imagingLEO beacons have good potential to improve 3D imagingover ground and LEO GNSS observationsAccurate low-elevation GNSS measurements will allowimproved imaging
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Acknowledgements
This research was supported by the AirForce Research Laboratory and NASA.
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ReferencesTS Kelso et al. Validation of sgp4 and is-gps-200d against gpsprecision ephemerides. 2007 "COSMIC-2." COSMIC 2. UCAR, n.d.http://www.cosmic.ucar.edu/cosmic2. 02 Jan. 2016.Yue, Xinan, et al. "Observing system simulation experimentstudy on imaging the ionosphere by assimilating observationsfrom ground GNSS, LEO-based radio occultation and oceanreflection, and cross link." IEEE Transactions on Geoscience andRemote Sensing 52.7 (2014): 3759-3773.Yue, Xinan, et al. "Global 3‐D ionospheric electron densityreanalysis based on multisource data assimilation." Journal ofGeophysical Research: Space Physics 117.A9 (2012).
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COSMIC (LEO-based)
horizontal TP speed
proportional to vertical TP speed
proportional to∣∣v ∣∣SV
∣∣v ∣∣ cos θSV SV
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images originally published at www.cosmic.ucar.edu
Occultationoccurrences over 24
hours for COSMICand COSMIC-2
COSMIC 2
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Mask/Filters
GPS 1 (for RX) elevation > threshold(5 degrees)closest approach of LEO ray-path toEarth surface > 2 km altitude
proximity < threshold (100 km)common-volume altitude < threshold (1500 km)
Ray pathsthrough Earth
Volumes wayout in space
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