Ionosphere Observability Using GNSS and LEO...

Ionosphere ObservabilityUsing GNSS and LEO

Platforms

Brian BreitschAdvisor: Dr. Jade Morton

1

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

2

Image credit: NASA/J. Grobowsky 2014

3

Image credit:

NASA

4

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)

5

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

6

"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

7

GNSS Ground ReceiversGPS Lab

High-rate GNSSdata collection

network

IGSStation Map

GNSS network data available

from many sources: IGS,

CORS, ARGN, etc.

8

Ground RXObservations

GNSS sky plots

9

Ground RXObservations 700 km 400 km 100 km

60°

30°

0°

GNSS signalionosphere piercingpoints for groundreceiver atlow/mid/high latitude5° elevation mask

IPP

10

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.

11

LEO Occultations 90-day scatter of COSMIC-GPS

occultation tangent points

top coords. bottom coords.

tangent point altitude histogram

12

LEO Occultations

90-day histogram ofCOSMIC-GPS occultationtangent point azimuths

13

Geometry

common observation volume

RO tangent point

Ground/LEO Common Volume

14

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

15

Ground/LEOCommonVolume

60°

40°

20°

0°

6-satellite constellation

750 km altitude

24° inclination

16

Ground/LEOCommonVolume

60°

40°

20°

0°

6-satellite constellation

750 km altitude

72° inclination

17

Ground/LEOCommonVolume

6-satellite constellation

750 km altitude

24° and 72° inclination

18

LEO BeaconObservations

LEO constellationground track coverage72° incl.

LEO beacon IPP@ 150 km and 20° elev. if we had beacon RX at every IGS station

19

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

20

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

22

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

23

Acknowledgements

This research was supported by the AirForce Research Laboratory and NASA.

24

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).

25

COSMIC (LEO-based)

horizontal TP speed

proportional to vertical TP speed

proportional to∣∣v ∣∣SV

∣∣v ∣∣ cos θSV SV

26

images originally published at www.cosmic.ucar.edu

Occultationoccurrences over 24

hours for COSMICand COSMIC-2

COSMIC 2

27

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

28