Transcript The Doppler Wind Experiment

The Huygens Doppler Wind Experiment:
Results from Titan
Michael Bird
(Radiostronomisches Institut, Universität Bonn)
And the DWE Team
EGU Vienna - April 25, 2005
The DWE Team
• M.K. Bird, R. Dutta-Roy, Y. Dzierma
Radioastronomisches Inst., Univ. Bonn, Auf dem Hügel 71, 53125 Bonn, Germany
• M. Allison
NASA Goddard Inst. for Space Studies, 2880 Broadway, New York, NY 10025, USA
• D.H. Atkinson
Dept. of Elec. & Computer Engineering, Univ. of Idaho, Moscow, ID 83844, USA
• S.W. Asmar, W.M. Folkner, D.V. Johnston, R.A. Preston
Jet Propulsion Laboratory, Caltech, 4800 Oak Grove Dr, Pasadena, CA 91109, USA
• P. Edenhofer
Institut für HF-Technik, Universität Bochum, 44780 Bochum, Germany
• D. Plettemeier
Elektrotechnisches Institut, Technische Univ. Dresden, 01062 Dresden, Germany
• G.L. Tyler
Center for Radar Astronomy, Stanford University, Stanford, CA 94305, USA
• L.I. Gurvits, S.V. Pogrebenko, I.M. Avruch
Joint Inst. for VLBI in Europe, P.O. Box 2, 7990 AA Dwingeloo, The Netherlands
Vienna EGU, 25 April 2005
Huygens DWE
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DWE Concept
•
•
•
Goal: In situ determination of zonal wind
speed along Huygens descent path
Approach: Record Doppler effect on
Huygens carrier signal => radial velocity
Input parameters:
1. Huygens descent speed, meridional speed
2. Huygens starting position
3. Cassini position & velocity
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Huygens DWE
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DWE Hardware
Ultra-stable Oscillators (USOs)
• TUSO on
Huygens
Probe
• RUSO in
Huygens
Receiver on
Cassini
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Huygens Signal paths
TCXO
TCXO
Channel B
Huygens Data
Cassini
TCXO
RUSO
Channel A
TCXO
TUSO
Huygens
Probe
Huygens
Receivers
“Channel C”
Earth
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DWE from Earth: Geometry
• Huygens antenna
pointed only ~30° from
Earth
• Better SNR than for
Galileo Probe detection
at Jupiter
• Probe velocity
projection in direction
to Earth nearly
antiparallel to
projection in direction
to Orbiter
Vienna EGU, 25 April 2005
75°
60°
45°
30°
15°
240°
210°
Track of Orbiter
180°
150°
Probe
120°
0°
-15°
20º
-30°
Track of
Sub-Earth
Point
-45°
-60°
-75°
Huygens DWE
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Huygens Radio Tracking Net
GBT
VLBA
OV
PT
KP
MK
VLBA
MK
Parkes
10:18 UTC-GRT
Vienna EGU, 25 April 2005
12:30 UTC-GRT
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Huygens VLBI Network
Facility
Start UTC
Stop UTC
GBT
09:31:10
12:15:00
VLBA Fort Davis
09:31:10
13:45:00
VLBA North Liberty
09:31:10
13:15:00
VLBA Owens Valley
09:30:09
14:49:14
DWE: No nodding – on Titan continuously
VLBA Pie Town
09:30:11
14:15:04
DWE: No nodding – on Titan continuously
VLBA Los Alamos
09:31:10
14:00:00
VLBA Brewster
09:31:10
14:48:00
VLBA Kitt Peak
09:31:10
14:15:00
DWE
VLBA Mauna Kea
09:31:10
16:00:00
DWE
Parkes
12:26:23
16:00:00
DWE: Real time RSR detection
Hobart
11:13:10
16:00:00
Ceduna
10:13:10
16:00:00
Mopra
10:10:10
16:00:00
Kashima
09:31:10
16:00:00
Shanghai
10:01:10
16:00:00
Urumqi
11:31:10
16:00:00
Calibration only, no Huygens signal at 2040 MHz
ATCA
10:01:10
16:00:00
Calibration only, no Huygens signal at 2040 MHz
Onsala
19:01:10
22:15:00
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2005
21:46:10
Wettzell
22:15:00
Comment
DWE: Real time RSR detection
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GBT
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Parkes
Huygens DWE
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10 UTC-GRT
10:18:15
GBT
Huygens!
just(~
noise
-171 dBm)
Flux density  125 Jy
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Huygens Frequency: GBT + Parkes
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Huygens Frequency: GBT + predicts
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Huygens Frequency: Parkes + Predicts
predicted
impact
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Parkes: Huygens Impact on Titan
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Zonal Wind Retrieval
Doppler shift:
where
vLS
fR    f 0
c
    
vLS  (v des  v NS  v EW  v C )  nLS
= radial velocity between transmitter and receiver
1
 vEW 
(vLS  vC  cosC  vdes  cosdes  vNS  cosNS )
cosDWC
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Doppler Components
GBT
(1) Raw Doppler
(2) Only Huygens
Motion
(3) Huygens Descent
Velocity
(4) Huygens Horizontal
Velocity
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Zonal Wind Velocity
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Zonal Wind Height Profile
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DWE: Preliminary Results
• Zonal winds above boundary layer are
PROGRADE
• Huygens drifted 3.95º (~175 km) eastward
• Low-velocity layer between 60-100 km
– Stong positive/negative wind shear
– ‘Unexpected’, but evident in some models
• Considerable turbulence above 100 km
• Near surface winds are weak (~ 1-2 m/s)
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