gps occultation on clarreogps occultation on clarreo stephen leroy, jim anderson, john dykema...

GPS Occultation On CLARREOGPS Occultation On CLARREO

Stephen Leroy, Jim Anderson, John Dykema

Harvard University

(and Rob Kursinski, George Hajj, Chi Ao, Tony Mannucci, Michael Gorbunov, Uli Foelsche, Larry

Young, Byron I’ijima, etc.)

July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 2

OutlineOutline

• Science Traceability– Testing climate models by constraining feedbacks

– Climate response, detection times, accuracy requirements

• GPS Radio Occultation– A radio occultation primer

– Derived products

– GPS/MET, CHAMP, COSMIC

• Traceability– Double-differencing

– Ionospheric influence

– Critical refraction & the lower troposphere

• CLARREO Requirements– Rising and setting occultations, open loop, GALILEO capable

– Establish traceability, archiving data and software


Testing Climate ModelsTesting Climate Models

dT

dx

x

F

dT

dx

x

F

i

ii

i

ii

∂∂=⇒

∂∂=⇒

SWSW

LWLW

γ

γ

1

SWLWrad

−

−−Γ×∆=∆ ∑∑i

ii

iFT γγ

Response = Forcing × Sensitivity

Longwave feedbacks

Shortwave feedbacks


Information in InfraredInformation in Infrared

-20

-10

0

10

Tropospheric Temperature Signal Stratospheric Temperature Signal

500 1000 1500 2000

-20

-10

0

10

Water Vapor Signal

d(R

adia

nce)

/dt [

10-8 W

cm

-2 (

cm-1)-1

sr-1

dec

ade-1

]

Frequency [cm-1]

500 1000 1500 2000

Carbon Dioxide Signal

Obtain part of feedbacks

1−

×

∂∂=

dt

dT

dt

dx

x

F i

iiγ


Information in GPS OccultationInformation in GPS OccultationGFDL-CM2.0

0

10

20

30GFDL-CM2.1 GISS-AOM GISS-EH

GISS-ER

0

10

20

30INM-CM3.0 IPSL-CM4 MIROC3.2(medres)

ECHAM5/MPI-OM

-600600

10

20

30MRI-CGCM2.3.2

-60060

CCSM3

-60060

PCM

-60060

-0.2 0.0 0.2 0.4 0.6 0.8d(ln pN)/dt (% decade-1)

Obtain climate “response” by observing jet stream migration, widening of Hadley cell, expansion of troposphere.

Obtain response to 10% uncertainty in 29 years (SRES-A1B).

1−

×

∂∂=

dt

dT

dt

dx

x

F i

iiγ


Fingerprinting OccultationFingerprinting Occultation

Leroy, Anderson, Dykema, 2007: J. Geophys. Res.


Accuracy RequirementsAccuracy Requirements

90 60 30 0 -30 -60 -90Latitude

0

5

10

15

20

Hei

ght (

km)

0

2

4

6

8

10

Req

uire

d A

ccur

acy

in G

eopo

tent

ial H

eigh

t [m

]

From Leroy, Anderson, Ohring (2007):

h ~ 2 m

N/N ~ 0.0002

(dL/dt) ~ 0.4 mm/s

yrs6/5.0/vm σσ =


Radio Occultation: A Timing MeasurementRadio Occultation: A Timing Measurement

vGPS

φGPS

p

vLEO

φLEO

p

ε

LEOLEOGPSGPS coscos φφνλ vvdt

dL +=∆=−

GPS LEO


Processing AlgorithmsProcessing Algorithms

• Orbit determination and clock correction, GPS and LEO: dL/dt

• Diffraction (and multipath) inversion: ε(p)

• Inversion for refractivity: N(r)

∫∞

−′′′

=p pp

pdppn

22

)(1)(

επ

Kursinski, E.R., G.A. Hajj, J.T. Schofield, R.P. Linfield, and K.R. Hardy, 1997: Observing Earth’s atmosphere with radio occultation measurements using the Global Positioning System. J. Geophys. Res., 102, 23429-23465.

Hajj, G.A., E.R. Kursinski, W.I. Bertiger, L.J. Romans, and S.S. Leroy, 2002: A technical description of atmospheric sounding by GPS occultation. J. Atmos. Solar-Terr. Phys., 64, 451-469.

Gorbunov, M.E., H.H. Benzon, A.S. Jensen, M.S. Lohmann, and A.S. Nielsen, 2004: Comparative analysis of radio occultation processing approaches based on Fourier integral operators. Radio Sci., 39, doi:10.1029/2003RS002916.

dSn

U

s

e

s

e

nUpU

S

iksiks

∫∫

∂∂−

∂∂=

π4

1)(


Derived ProductsDerived Products

• Refractivity

• “Dry” pressure

• Geopotential height

2w1-231-6 )hPaK10363()hPaK6.77(10)1(

T

p

T

pnN ×+=×−=

∫∫ +≅×=∞

−)(

0

1-4 )K7521()()mhPa10402.4()(hp

h

d T

dpqhpdhNhp

hhp t

pH

t

pH

t

h

∂∂≈

∂∂=

∂∂ dlnln


Heritage (1)Heritage (1)

GPS-MET, TurboRogue

UCAR, 1995-1997

“Selective availability”

Anti-spoofing turned off during four prime-time periods

Aft-viewing low-gain antenna, no open-loop

CHAMP, BlackJack

GFZ Potsdam, 2001-present


Anti-spoofing handling on GPS receiver

Aft-viewing high-gain antenna, no open-loop



GPS-MET, TurboRogue

UCAR, 1995-1997


Anti-spoofing turned off during four prime-time periods

Aft-viewing low-gain antenna, no open-loop

CHAMP, BlackJack

GFZ Potsdam, 2001-present



Aft-viewing high-gain antenna, no open-loop



COSMIC, IGOR (BlackJack)

Six satellites

Taiwan, UCAR, NASA, NSF, 2006-present

“Selective availability” off


Fore- and aft-viewing high-gain antennas, with open-loop

PYXIS-RO (Broad Reach)

New GPS, GALILEO, open-loop

TOGA1/2 (NASA/JPL)

New GPS, GALILEO, GLONASS(?), steerable antennas




Six satellites







TOGA1/2 (NASA/JPL)



Calibration: Double DifferencingCalibration: Double Differencing

Hardy, K.R., G.A. Hajj, and E.R. Kursinski, 1994: Accuracies of atmospheric profiles obtained from GPS occultations. Int. J. Sat. Comm., 12, 463-473.


Ground NetworkGround Network

International GNSS Service: High-rate GPS and GALILEO clock calibration

International GNSS Service: Orbit determination for GPS and GALILEO satellites


IonosphericIonospheric InfluenceInfluence

Refractivity fractional error, %

Ray

heig

ht,k

m

-40 -20 0 20 400

10

20

30

40

50Gorbunov & Leroy: In preparation.

Realistic ionosphericscintillation superimposed on simulated radio occultation data. Statistics of retrievals with and without ionospheric scintillation.


Testing TraceabilityTesting Traceability

Two methods

Intercomparison of different implementations (Hajj et al. 2004)

Comparison of trend determinations deduced by different groups (ROTrendsProject)


GPS on CLARREOGPS on CLARREO

1

SWLWrad

−

−−Γ×∆=∆ ∑∑i

ii

iFT γγ

Response = Forcing × SensitivityGPS occultation is essential on CLARREO to measure the climate “response”.

Combined with an IR instrument, obtain longwave gain constants

iLW.

Combined with a SW instrument, obtain shortwave gain constants

iSW.

Create a prototype, self-contained, independent climate benchmark satellite fully able to test climate models, suited for an operational NOAA climate monitoring program.


Science Requirements for CLARREOScience Requirements for CLARREO

• Achieve S.I. traceability to 0.4 mm/s.

– Either on-board USO or double-differencing

– Open-loop tracking

• Data density

– Antennas fore and aft to obtain ~500 daily soundings. With GALILEO, ~1000 daily soundings.

– Account for diurnal cycle: three LEOs spaced 60° in nodal longitude or LEOs in 90° inclination orbit(s).

• Archival

– Phase data for orbits & occultation

– Receiver software

gps occultation on clarreogps occultation on clarreo stephen leroy, jim anderson, john dykema...

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