EP 8.2: DPG, Berlin - March 7, 2005

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EP 8.2 DPG, Berlin - March 7, 2005

• The Huygens Doppler Wind Experiment
• Initial Results

Michael Bird (Radiostronomisches Institut,
Universität Bonn) And the DWE Team
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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 gt radial velocity
• Input parameters
• Huygens descent speed, meridional speed
• Huygens starting position
• Cassini position velocity

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Huygens Descent Paths on Titan
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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 Doppler PCO1
TUSO/RUSO
TCXO/TCXO
3 hours
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No power!
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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

?20º
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Huygens Radio Tracking Net
1018 UTC-GRT
1230 UTC-GRT
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Huygens VLBI Network
Facility Start UTC Stop UTC Comment
GBT 093110 121500 DWE Real time RSR detection
VLBA Fort Davis 093110 134500
VLBA North Liberty 093110 131500
VLBA Owens Valley 093009 144914 DWE No nodding on Titan continuously
VLBA Pie Town 093011 141504 DWE No nodding on Titan continuously
VLBA Los Alamos 093110 140000
VLBA Brewster 093110 144800
VLBA Kitt Peak 093110 141500 DWE
VLBA Mauna Kea 093110 160000 DWE
Parkes 122623 160000 DWE Real time RSR detection
Hobart 111310 160000
Ceduna 101310 160000
Mopra 101010 160000
Kashima 093110 160000
Shanghai 100110 160000
Urumqi 113110 160000 Calibration only, no Huygens signal at 2040 MHz
ATCA 100110 160000 Calibration only, no Huygens signal at 2040 MHz
Onsala 190110 221500
Wettzell 214610 221500
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GBT
Parkes
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101810 UTC-GRT
GBT
just noise
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101815 UTC-GRT
GBT
Huygens! ( -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
Error Analysis
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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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DWE Preliminary Results

• Zonal winds above boundary layer are PROGRADE
• Low-velocity layer between 60-80 km
• Stong positive/negative wind shear
• Unexpected, but evident in some GCMs
• Considerable turbulence above 100 km
• Near surface winds are weak ( 1-2 m/s)