Monitoring the Ionosphere and Neutral Atmosphere with GPSgauss.gge.unb.ca/papers.pdf/DASP2002.pdf · RBL/DASP 20 Feb. 02 Monitoring the Ionosphere and Neutral Atmosphere with GPS

Geodetic Research Laboratory • Department of Geodesy and Geomatics Engineering • University of New Brunswick

RBL/DASP20 Feb. 02

Monitoring the Ionosphere andNeutral Atmosphere with GPS

Richard B. Langley

Division of Atmospheric and Space Physics WorkshopFredericton, N.B. • 21-23 February 2002

Geodetic Research LaboratoryDepartment of Geodesy and Geomatics Engineering

University of New BrunswickFredericton, N.B.


RBL/DASP20 Feb. 02

Outline

• Introduction to GPS

• Current status

• Modernization

• The GPS Signals

• Atmospheric Propagation Delay

• Neutral Atmosphere

• Ionosphere

• Spaceborne GPS Limb Sounding

• Ionospheric Tomography

• Concluding Remarks


RBL/DASP20 Feb. 02

GPS Segments


RBL/DASP20 Feb. 02

GPS Constellation

Altitude: 20,200 km

Orbital Period: 12 hrs(semi-synchronous)

Orbital Plane: 55 degrees

Number of Planes: 6

Vehicles per plane: 4-5

Constellation size: >24 satellites (currently 28)


RBL/DASP20 Feb. 02

Generations of Satellites

Block I Prototype (test) satellites. 10 launched between 1978 and 1985. All retired.

Block II Initial operational satellites. 9 launched between1989 and 1990. 4 still functioning.

Block IIA Slightly modified Block IIs. 19 launched between 1990 and 1997. 18 still functioning.

Block IIR Replenishment satellites. 6 orbited to date. First in 1997. C/A code on L2 plus higher poweron last 12 satellites launched from 2003 onwards.

Block IIF Follow-on satellites. New civil signal at 1176.45MHz. First launch expected in 2005.

Block III Conceptual.


RBL/DASP20 Feb. 02

Block IIR Satellite


RBL/DASP20 Feb. 02

GPS Operation

MonitorStationGround

Antenna

Master ControlStation (Schriever AFB)

NavigationMessage

(SpacecraftTime andPosition)

24-satellite (nominal)constellation

L21227.6 MHz

C/A -codeP(Y)-code

L11575.42 MHz

Receiver Calculates3-D Location and

Time


RBL/DASP20 Feb. 02

GPS Modernization

• One goal is enhanced capabilities for civil users of GPS

• Civil benefits include:

– Selective Availability (SA) turned off on 2 May 2000

– Second civil frequency for ionospheric correction andredundancy

– Third civil signal for “safety of life” applications inprotected spectrum; more robust; also provides highaccuracy and benefits real-time applications


RBL/DASP20 Feb. 02

Selective Availability Switched Off


RBL/DASP20 Feb. 02

GPS Modernization Details

• Last 12 Block IIRs - Add second civil signal (C/A on L2)and new military signal (M-code). Provide more signalpower.

First modernized launch (Block IIR-M) - FY03

• First 6 Block IIFs (“IIF Lite”) - All of above capabilitiesplus new third civil signal in protected band (L5).

First Block IIF “Lite” launch - FY05

• At the current GPS satellite replenishment rate, all threecivil signals (L1-C/A, L2-C/A, and L5) will be available forinitial operational capability by 2010, and for fulloperational capability by approximately 2013.


RBL/DASP20 Feb. 02

Block IIF Satellite


RBL/DASP20 Feb. 02

Signal Modernization

1227 MHz 1575 MHz1176 MHzL2 L1L5

P(Y)P(Y)

C/AC/A

P(Y)P(Y)

C/AC/A

P(Y)P(Y)

P(Y)P(Y)

C/AC/A

P(Y)P(Y)

C/AC/A

P(Y)P(Y)

C/AC/AMM MM

Present Signal

Civil Non-AviationSignal (>2003)

Civil Aviation &New MilitarySignals (>2005)


RBL/DASP20 Feb. 02

Current GPS Signals


RBL/DASP20 Feb. 02

Observation Equations

P t t c dt t dt t I t T t trs

P( ) ( ) [ ( ) ( )] ( ) ( ) ( )= + − − + + +ρ τ εPseudorange:

Carrier phase:Φ

Φ

( ) ( )

( ) [ ( ) ( )] ( ) ( ) ( )

t t

t c dt t dt t I t T t N trs

=

= + − − − + + +

λ φ

ρ τ λ ε

t - signal reception timeλ - wavelengthc - speed of lightρ - geometric rangeτ - signal transit timedtr - receiver clock offset

dts - satellite clock offsetI - ionospheric delayT - tropospheric delayN - integer ambiguityεP - pseudorange noiseεΦ - carrier phase noise


RBL/DASP20 Feb. 02

Atmospheric Refraction

80 km

50 km

9-16 km

0 km

Ionosphere

Stratosphere

Tropopause

Troposphere

The

rmos

pher

eM

esos

pher

e

S′

S

τ = ∫ 1v

dSS


RBL/DASP20 Feb. 02

Phase and Group Delay

∆

Φ ∆

τ

τ

= − ′

=

= − ′

= − + − ′

= − + − ′

∫ ∫

∫ ∫

∫ ∫ ∫

∫ ∫ ∫

′

′

′

′

1 1

1

1

vdS

cdS

d c

n dS dS

n dS dS dS

dP n dS dS dS

S S

S S

S S S

g

S S S

( )

( )


RBL/DASP20 Feb. 02

Tropospheric Zenith Propagation Delay

Zenith Delay

T n r dr

N r dr

z = −[ ]

=

∫∫−

( )

( )

1

10 6

N KMM

PT

K KMM

eT

Ke

Td d

= + −

+1 2 1 3 2

where refractivity of air is given by (ignoring compressibility factors)

Hydrostatic “Wet”

N KPT

KeT

Ke

T= + +1 2 3 2

Dry Wetor


RBL/DASP20 Feb. 02

Slant Delay and PWV

T T m e T m ehz

h wz

w= +( ) ( )

mapping functions

zenith delays

Zenith hydrostatic delay computed from accurate surface pressure

Zenith wet delay (ZWD) estimated from GPS data

Pr ( )ecipitable Water Vapour PWV ZWD≈ ÷ 6


RBL/DASP20 Feb. 02

Precipitable Water Vapour from GPS


RBL/DASP20 Feb. 02

PWV from GOES Sounder


RBL/DASP20 Feb. 02

German GPS Met Network


RBL/DASP20 Feb. 02

Estimated Water Vapour Field

Integrated water vapour (IWV)= PWV • density of H2O

IWV(kg/m2)

15 August 200012:00 UT


RBL/DASP20 Feb. 02

Ionospheric Refractive Index

n X XY X XY

where

XNe

m fY

B em f

≅ − ± − − +( )

= =

112

12

18

14

1

41

21

2 2 2

2

20

20

cos cos

,

θ θ

π ε π

and θ is the angle between the direction of signal propagationand the geomagnetic field.

At the GPS L1 frequency, assuming N=1012, B0=0.5x10-4,θ=0,

n ≅ − × ± × − × − ×− − − −1 1 6 10 1 6 10 1 3 10 1 6 105 8 10 11. . . .

And so, to a good approximation: n = 1 - αN/f2 and ng = 1 + αN/f2


RBL/DASP20 Feb. 02

Phase Advance and Group Delay

ρ α ρ

ρ α ρ

α

Φ = ( ) = −

= −

= ( ) = +

= +

= ≅

∫ ∫

∫ ∫

∫

n dSN

fdS I

and

n dSN

fdS I

where If

N dSTEC

f

S S

P

S S

S

1

1

40 28

2

2

2 2.


RBL/DASP20 Feb. 02

Ionospheric Propagation Delay

If

f fP P

If

f fN N

L P L L P L L

L L L

122

22

12 1 2 1 2

122

22

12 1 1 2 2 1 2 1 2

( ) ( )

( ) ( )

=−

−[ ] +

=−

−( ) − −( )[ ] +

+

+

ε

λ λ εΦ ΦΦ Φ

Phase levelling:

I I

w I I

w

j

jn

n

j P j

j

jn

n= −

−[ ]=−

=−

∑

∑Φ

Φ

2

2

2

2

, ,


RBL/DASP20 Feb. 02

Ionospheric Shell Model


RBL/DASP20 Feb. 02

Ionospheric Shell Model

I t M e a t a t d a t d b brs

rs

r r rs

r rs

rs( ) ( ) ( ) ( ), , ,= ( ) + +[ ] + +0 1 2λ φ

stochastic parameters

difference inlongitudes ofpierce pointand Sun

difference ingeomagneticlatitudes ofpierce pointand receiver

receiver bias

satellitebias

mappingfunction

observable

M er e

r hE

E

( )cos= −+( )

−

12 2

2

1

2 e - elevation anglerE - mean Earth radiush - shell height


RBL/DASP20 Feb. 02

IGS Tracking Network

288 stations on 20 February 2002


RBL/DASP20 Feb. 02

Global TEC Map from IGS Data


RBL/DASP20 Feb. 02

WAAS Ionospheric Grid


RBL/DASP20 Feb. 02

Low Latitude Ionosphere Studies

South American Network• 37 stations from the IGSand RMBC (BrazilianNetwork for ContinuousMonitoring of GPS)• Map shows 23 of thestations


RBL/DASP20 Feb. 02

TEC Maps - St. Swithin’s Day Storm

Mean TEC 22:00 UT, 15 July 2000Mean TEC 22:00 UT, 14 July 2000


RBL/DASP20 Feb. 02

Ionospheric Scintillation Monitoring

Phase scintillation at Calgary on 22 March 2001


RBL/DASP20 Feb. 02

Spaceborne GPS Limb Sounding


RBL/DASP20 Feb. 02

CHAMP


RBL/DASP20 Feb. 02

Initial CHAMP Neutral Atmosphere Results

CHAMP datataken over theSouth Atlantic on 11 February 2001


RBL/DASP20 Feb. 02

Initial CHAMP Ionosphere Profile


RBL/DASP20 Feb. 02

Ionospheric Tomography


RBL/DASP20 Feb. 02

Concluding Remarks

• Monitoring and mapping the atmosphere is yet another application ofGPS

• Regional GPS networks are being established with the expressedpurpose of measuring atmospheric properties with the aim of introducingGPS-derived parameter values into weather models

• GPS techniques can contribute to our understanding of space weather

• Several GPS limb-sounding satellite missions have flown with more inthe planning stages including e-POP

• GPS modernization as well as other global navigation satellite systems(GLONASS, Galileo) will further enhance radiometric techniques forstudying the Earth’s atmosphere


RBL/DASP20 Feb. 02

Acknowledgements

Slide Organization3 The Aerospace Corporation4 Jet Propulsion Laboratory6 Lochheed Martin Space Systems9 U.S. SPACECOM11 The Boeing Company12 A.J. Van Dierendonck19 University Corporation for Atmospheric Research20 National Oceanic and Atmospheric Administration21 GeoForschungsZentrum Potsdam22 GeoForschungsZentrum Potsdam28 Jet Propulsion Laboratory33 A.J. Van Dierendonck and Q. Hua34 GeoForschungsZentrum Potsdam35 GeoForschungsZentrum Potsdam36 GeoForschungsZentrum Potsdam37 National Observatory of Athens

Documents

Monitoring the Ionosphere and Neutral Atmosphere with GPSgauss.gge.unb.ca/papers.pdf/DASP2002.pdf · RBL/DASP 20 Feb. 02 Monitoring the Ionosphere and Neutral Atmosphere with GPS