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Dr. David H. AtkinsonDept. Electrical & Computer Engineering
University of Idaho8 April 2005
Measuring the Zonal Winds on Titan:
The Huygens Probe Doppler Wind Experiment
Transmitter Ultrastable Oscillator (TUSO)
Radar Altimeter Antennas
GCMSAtmosphericStructure Instrument
Descent Imager
Surface SciencePackageCommand
Data ManagementUnit (CDMU)
Accelerometers
Titan: Pre-Cassini/HuygensN2, CH4, andH2 atmosphere cause a mild greenhouseeffect that raisesthe surface temperature by+21K.
High altitude optically thickorganic haze absorbs solarvisible but istransparent to IR, coolingsurface tempby about 9K.(anti-greenhouseeffect).
Huygens’ Scientific Payload
• ACP - Aerosol Collector and Pyrolyser (G. Israel, France)– Collection of aerosols for chemical-composition analysis.
• GCMS - Gas Chromatograph and Mass Spectrometer(H. Niemann, NASA GSFC)
– gas chemical analyser designed to identify and quantify various atmospheric constituents.
• DISR - Descent Imager & Spectral Radiometer (M. Tomasko, U. Arizona)
– images and spectral measurements. Also spectra of the surface material will be acquired.
• DWE - Doppler Wind Experiment (M. Bird, U. Bonn)– Wind measurements using Probe/Orbiter radio signal
• HASI - Huygens Atmosphere Instrument (M. Fulchignoni, Italy)
– physical and electrical properties of the Atmosphere
• SSP - Surface Science Package (J. Zarnecki, UK)– physical properties of the surface at the impact site
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
Ultra-stable Oscillators (USOs)• TUSO on Huygens Probe
• RUSO in Huygens Receiver on Cassini Orbiter
DWE Hardware
DWE from Earth: Geometry
0°
15°
30°
45°
60°
75°
-15°
-30°
-45°
-60°
-75°
Track ofSub-Earth
Point
Track of OrbiterProbe
180°210°240° 150° 120°
• 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
Huygens VLBI Network
Facility Start UTC Stop UTC Comment
GBT 09:31:10 12:15:00 DWE: Real time RSR detection
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
Wettzell 21:46:10 22:15:00
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)