Ionosphere Observability Using GNSS and LEO Platforms

Brian Breitsch

Advisor: Dr. Jade Morton

  • Motivate ionosphere TEC observations
  • Past work in ionosphere observability
  • Observation volume
    • Ground receivers
    • LEO radio occultations (RO)
    • Joint ground and LEO overhead/RO
    • LEO beacons
  • Data affects in simulated localized imaging

Image credit: NASA/J. Grobowsky 2014

Image credit: NASA

Ionosphere TEC

TEC = \int_{\text{rx}}^\text{sat} N_e(x) dx
TEC=∫rxsatNe(x)dxTEC = \int_{\text{rx}}^\text{sat} N_e(x) dx

observed by multi-frequency GNSS

LEO reflection

LEO occultation

LEO beacon

ground GNSS

LEO overhead

low Earth-orbiting (LEO)

Global Navigation Satellite System (GNSS)

Previous Work

  • 2D and 3D ionosphere maps of electron density from TEC measurements

Image Credit: "Multi-satellite ionosphere-plasmasphere

electron density reconstruction", GFZ Potsdam

  • climatological and large-scale

Wang Yang

"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"

Previous Work

Xinan Yue et. al. 2013

  • LEO occultations largely contribute to global-scale models due to lack of ground RX over oceans

GNSS Ground Receivers

GPS Lab

High-rate GNSS data collection network

IGS

Station Map

GNSS network data available from many sources: IGS, CORS, ARGN, etc.

Ground RX Observations

GNSS sky plots

Ground RX Observations

700 km

400 km

100 km

60°

30°

0°

GNSS signal ionosphere piercing points for ground receiver at low/mid/high latitude

5° elevation mask

IPP

LEO Receiver Observations

orbital altitude: between 500-800 km

orbital inclination: 24° or 72°

occultation tangent point (TP)

e.g. COSMIC/COSMIC-2

  • use POD antenna
  • highly localized to LEO satellite
  • use occultation antennas
  • traverse large ionosphere volume

Radio Occultations (RO)

Overhead Obs.

LEO Occultations

90-day scatter of COSMIC-GPS occultation tangent points

top coords.

bottom coords.

tangent point altitude histogram

LEO Occultations

90-day histogram of COSMIC-GPS occultation tangent point azimuths

Geometry

common observation volume

RO tangent point

Ground/LEO Common Volume

3D Line-Segment Intersection

  • common-volume point-of-interest
    • midpoint b/w points of closest approach
    • GNSS rays <100 km apart

"the points of closest approach between two line segments"

*must handle special case where point of closest approch is on segment endpoint.

Ground/LEO Common Volume

Ground/LEO Common Volume

60°

40°

20°

0°

  • 6-satellite constellation

  • 750 km altitude

  • 24° inclination

Ground/LEO Common Volume

60°

40°

20°

0°

  • 6-satellite constellation

  • 750 km altitude

  • 72° inclination

Ground/LEO Common Volume

  • 6-satellite constellation

  • 750 km altitude

  • 24° and 72° inclination

LEO Beacon Observations

LEO constellation ground track coverage

72° incl.

LEO beacon IPP

@ 150 km and 20° elev.

if we had beacon RX at every IGS station

Simulated Effects on Localized Imaging

  • regional IGS network in Europe
  • latitudes
    • 43°-53° @ 0.25° sep.
  • longitudes
    • 6°-15° @ 3° sep.
  • altitudes
    • 100-980 km @ 20 km
  • attempt to reconstruct IRI image with depletion feature from uniform density starting image

Simulated Effects on Localized Imaging

ground

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

Future Work

  • Low elevation ground GNSS esspecially important at low altitude
  • use 3-frequency GNSS measurements to address low-elevation TEC estimation

20° el. mask

5° el. mask

Conclusions

  • Poleward deficit of GNSS satellites causes gap in information from ground receivers
  • Occurrence of ground and LEO GNSS observations in common volume heavily depends upon LEO constellation orbital inclination
  • Overhead and RO LEO observations aid in topside ionosphere imaging
  • LEO beacons have good potential to improve 3D imaging over ground and LEO GNSS observations
  • Accurate low-elevation GNSS measurements will allow improved imaging

Acknowledgements

This research was supported by the Air Force Research Laboratory and NASA.

References

  • TS Kelso et al. Validation of sgp4 and is-gps-200d against gps precision 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 experiment study on imaging the ionosphere by assimilating observations from ground GNSS, LEO-based radio occultation and ocean reflection, and cross link." IEEE Transactions on Geoscience and Remote Sensing 52.7 (2014): 3759-3773.

  • Yue, Xinan, et al. "Global 3‐D ionospheric electron density reanalysis based on multisource data assimilation." Journal of Geophysical Research: Space Physics 117.A9 (2012).

COSMIC (LEO-based)

horizontal TP speed proportional to

vertical TP speed proportional to

||v_{SV}||
∣∣vSV∣∣||v_{SV}||
||v_{SV}||\cos\theta_{SV}
∣∣vSV∣∣cosθSV||v_{SV}||\cos\theta_{SV}

images originally published at www.cosmic.ucar.edu

Occultation occurrences over 24 hours for COSMIC and COSMIC-2

COSMIC 2

Mask/Filters

  • GPS 1 (for RX) elevation > threshold (5 degrees)
  • closest approach of LEO ray-path to Earth surface > 2 km altitude

Ray paths through Earth

  • proximity < threshold (100 km)
  • common-volume altitude            < threshold (1500 km)

Volumes way out in space