gps occultation on clarreogps occultation on clarreo stephen leroy, jim anderson, john dykema...
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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
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 3
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
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 4
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
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 5
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
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 6
Fingerprinting OccultationFingerprinting Occultation
Leroy, Anderson, Dykema, 2007: J. Geophys. Res.
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 7
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 =
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 8
Radio Occultation: A Timing MeasurementRadio Occultation: A Timing Measurement
vGPS
φGPS
p
vLEO
φLEO
p
ε
LEOLEOGPSGPS coscos φφνλ vvdt
dL +=∆=−
GPS LEO
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 9
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)(
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 10
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
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 11
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
“Selective availability”
Anti-spoofing handling on GPS receiver
Aft-viewing high-gain antenna, no open-loop
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 12
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
“Selective availability”
Anti-spoofing handling on GPS receiver
Aft-viewing high-gain antenna, no open-loop
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 13
Heritage (2)Heritage (2)
COSMIC, IGOR (BlackJack)
Six satellites
Taiwan, UCAR, NASA, NSF, 2006-present
“Selective availability” off
Anti-spoofing handling on GPS receiver
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
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 14
Heritage (2)Heritage (2)
COSMIC, IGOR (BlackJack)
Six satellites
Taiwan, UCAR, NASA, NSF, 2006-present
“Selective availability” off
Anti-spoofing handling on GPS receiver
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
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 15
Heritage (2)Heritage (2)
COSMIC, IGOR (BlackJack)
Six satellites
Taiwan, UCAR, NASA, NSF, 2006-present
“Selective availability” off
Anti-spoofing handling on GPS receiver
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
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 16
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.
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 17
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.
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 18
Ground NetworkGround Network
International GNSS Service: High-rate GPS and GALILEO clock calibration
International GNSS Service: Orbit determination for GPS and GALILEO satellites
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 19
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.
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 20
Testing TraceabilityTesting Traceability
Two methods
Intercomparison of different implementations (Hajj et al. 2004)
Comparison of trend determinations deduced by different groups (ROTrendsProject)
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 21
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.
July 17, 2007 Leroy, Anderson, Dykema: GPS Occultation 22
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