Single Station GPS Ionospheric Corrections Joe Malins 12/9/2016 - - PowerPoint PPT Presentation

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Single Station GPS Ionospheric Corrections Joe Malins 12/9/2016 - - PowerPoint PPT Presentation

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Single Station GPS Ionospheric Corrections Joe Malins 12/9/2016 1 1 Statement of Problem Want Faraday rotation to measure magnetic field of sun and CMEs Currently: IONEX Files: use global models involving hundreds of GPS

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SLIDE 1

Single Station GPS Ionospheric Corrections

Joe Malins

1 12/9/2016 1

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SLIDE 2

2 JPL Global Ionospheric TEC Map

Stovall, Kevin (UNM)

Statement of Problem

  • Want Faraday rotation to

measure magnetic field of sun and CMEs

  • Currently: IONEX Files:
  • use global models involving

hundreds of GPS stations

  • Problem: not many GPS

receivers located near LWA

  • Problem: Global models

update approximately every hour.

  • Time of Appreciable Change ~10

min

12/9/2016 2

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SLIDE 3

3

Dual Frequency GPS Antenna

LWA

Equipment

  • NovAtel 4004B Dual Frequency GPS
  • Borrowed from Air Force Research Lab

Scintillation Network Decision Aid (SCINDA) program

  • Self-biasing, 10s resolution,

Plasmasphere correction

12/9/2016 3

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SLIDE 4
  • Using Polarized Pulsars
  • Three contributions to rotation

measure:

  • Material surrounding pulsar
  • Interstellar/Interplanetary Medium
  • Ionosphere and near earth plasma
  • Assume near constant ISM and

material surrounding pulsar

  • r at least changing on long time scales
  • At large sun angles Short time scale

change only due to ionosphere

  • Find rotation measure, measure

ionospheric contribution, fit RM curve to ionosphere

4

See Veronica Dike (UNM) Poster

RM measurement

12/9/2016 4

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SLIDE 5

5

Different frequencies are delayed different amounts Receiver GPS

Ionosphere Measurement

  • Dual Frequency: 1575.42 MHz

and 1227.60 MHz

  • Ionosphere is plasma
  • Plasmas causes group velocity

delay, phase velocity increase in EM waves

  • Delays are strongly frequency

dependent

  • Integrated electron density:

Total Electron Content (TEC)

  • Measured in ne/m2 or TEC units

(TECU) 1 TECU = 1016 ne/m2

  • No profile information

Lower Ξ½ is delayed more Ionosphere

12/9/2016 5

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SLIDE 6

Better Corrections

6

Interpolated Observation at LWA1 at 2016/10/14 12:00:00 UTC

  • Each satellite provides

accurate data to a single point on the sky

  • Between 7-14 satellites

at any given time

  • For points between

satellites, use linear weighted average of satellites

𝜍 = 1 βˆ‘ 1 π‘’π‘š π‘ˆπΉπ· = βˆ‘ 𝜍 π‘’π‘š π‘ˆπΉπ·1

12/9/2016 6

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SLIDE 7

12/9/2016 7

JPL Model CODE Model GPS Observation Pulsar: B0950+08 3x 2Hour Observations (Black Dashed Lines) Date: 2016/09/23 πœ“2 = 0.6725 πœ“2 = 3.5999 πœ“2 = 0.3061

1.4 0.6 2.0 1.0 2.0 1.0 RM:

𝑠𝑏𝑒 𝑛2

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SLIDE 8

12/9/2016 8

JPL Model CODE Model GPS Observation πœ“2 = 3.6780 πœ“2 = 1.4576 πœ“2 = 0.2520

1.6 0.8 2.5 1.0 2.0 1.0

Pulsar: B0950+08 3x 2Hour Observations (Black Dashed Lines) Date: 2016/10/05

RM:

𝑠𝑏𝑒 𝑛2

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SLIDE 9

12/9/2016 9

JPL Model CODE Model GPS Observation Pulsar: B0950+08 3x 2Hour Observations (Black Dashed Lines) Date: 2016/10/14 πœ“2 = 25.2052 πœ“2 = 1.6509 πœ“2 = 0.7628

3.0 1.5 3.5 1.5 4.0 2.0 RM:

𝑠𝑏𝑒 𝑛2

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SLIDE 10

10

  • C. Sotomayor-Beltran et al.: Ionospheric Faraday rotation

Height Dependence

  • Current model : Thin Shell

Model

  • Attempt electrons

distributed along profile

  • 1st Try:
  • 191 points along

International Reference Ionosphere (IRI)

  • 2nd Try:
  • AFRL Ionosonde data from

AFRL at Kirtland

12/9/2016 10

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SLIDE 11

11 GPS with height correction GPS without height correction 12/9/2016 11

Height Corrected: πœ“2 = 0.5631 Not Height Corrected: πœ“2 = 0.3061

2016/09/23

Height Corrected Not Height Corrected

RM:

𝑠𝑏𝑒 𝑛2

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SLIDE 12

12/9/2016 12

Height Corrected: πœ“2 = 0.3813 Not Height Corrected: πœ“2 = 0.2521

2016/10/05

Height Corrected Not Height Corrected

RM:

𝑠𝑏𝑒 𝑛2

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SLIDE 13

12/9/2016 13

Height Corrected: πœ“2 = 0.9674 Not Height Corrected: πœ“2 = 0.7628

2016/10/14

Height Corrected Not Height Corrected

RM:

𝑠𝑏𝑒 𝑛2

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SLIDE 14

12/9/2016 14

𝑂(β„Ž) 𝑂𝑛 = 𝑇 β„Ž

βˆ’1/2 exp{1

2 [1 βˆ’ 𝑍 βˆ’ exp(𝑍)]} 𝑍 = 1 β„Žπ‘›

β„Žπ‘› β„Ž

π‘’β„Ž 𝑇 β„Ž 1 𝑇 β„Ž = 1 𝑇1(β„Ž) + 1 𝑇2(β„Ž) 𝑇1(β„Ž) = 𝑑1 sech2 β„Ž β„Žπ‘› βˆ’ 1 𝛾 β„Žπ‘›

βˆ’1

𝑇2(β„Ž) = 𝑑2 1 + β„Ž β„Žπ‘›

2 𝛽

β„Ž β„Žπ‘›

NSUMEI ET AL.: NEW VARY-CHAP TOPSIDE PROFILE (2012) Data from Stephen White AFRL

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SLIDE 15

What’s happening

Several Options

  • IGRF12 is not reporting accurate Magnetic Field
  • Seems unlikely due to stability of magnetic field
  • TEC from GPS in inaccurate
  • TEC compares very well to other GPS in area
  • Very similar to SCINDA GPS at Sevilleta
  • Profile is in accurate
  • Profile is more concentrated around Ionosphere F layer

12/9/2016 15

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SLIDE 16

16 Shao, X.-M., and E. H. Lay (2016) COHEN & R̈OTTGERING

Near Term Plans

  • Continue to use GPS to calibrate data for

low frequency observations

  • Eventually, want to use GPS Corrections

for correlating LWA1 and LWA Sevilleta

  • Can provide data universally for

interested parties for VLA corrections

  • Updated JPL IONEX files with GPS overlay

and 1min time resolution

12/9/2016 16