EP 8.2: DPG, Berlin - March 7, 2005 The Huygens Doppler Wind Experiment: Initial Results Michael Bird (Radiostronomisches Institut, Universität Bonn) And.

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

7 March 2005 2EP 8.2: DPG, Berlin

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

7 March 2005 3EP 8.2: DPG, Berlin

Huygens Descent Paths on Titan

7 March 2005 4EP 8.2: DPG, Berlin

DWE Hardware

• TUSO on Huygens Probe

• RUSO in Huygens Receiver on Cassini

Ultra-stable Oscillators (USOs)

7 March 2005 5EP 8.2: DPG, Berlin

Huygens Doppler: PCO#1TUSO/RUSO

TCXO/TCXO

3 hours

7 March 2005 6EP 8.2: DPG, Berlin

No power!

7 March 2005 7EP 8.2: DPG, Berlin

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

0°

15°

30°

45°

60°

75°

-15°

-30°

-45°

-60°

-75°

Track ofSub-Earth

Point

Track of OrbiterProbe

180°210°240° 150° 120°

20º

7 March 2005 8EP 8.2: DPG, Berlin

Huygens Radio Tracking Net

10:18 UTC-GRT 12:30 UTC-GRT

7 March 2005 9EP 8.2: DPG, Berlin

Huygens VLBI NetworkFacility 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

7 March 2005 10EP 8.2: DPG, Berlin

GBT Parkes

7 March 2005 11EP 8.2: DPG, Berlin

10:18:10 UTC-GRT

GBT just noise

7 March 2005 12EP 8.2: DPG, Berlin

GBT Huygens!(~ -171 dBm)

Flux density 125 Jy

10:18:15 UTC-GRT

7 March 2005 13EP 8.2: DPG, Berlin

Huygens Frequency: GBT + Parkes

7 March 2005 14EP 8.2: DPG, Berlin

Huygens Frequency: GBT + predicts

7 March 2005 15EP 8.2: DPG, Berlin

Huygens Frequency: Parkes + Predicts

predictedimpact

7 March 2005 16EP 8.2: DPG, Berlin

Parkes: Huygens Impact on Titan

7 March 2005 17EP 8.2: DPG, Berlin

Zonal Wind Retrieval

LSCEWNSdesLS nvvvvv

)(

)coscoscos(cos

1NSNSdesdesCCLS

DWC

EW vvvvv

xx

vx

EW

)err(

0fc

vf

LS

R Doppler shift:

Error Analysis:

7 March 2005 18EP 8.2: DPG, Berlin

GBT

(1) Raw Doppler

(2) Only Huygens Motion

(3) Huygens Descent Velocity

(4) Huygens Horizontal Velocity

Doppler Components

7 March 2005 19EP 8.2: DPG, Berlin

7 March 2005 20EP 8.2: DPG, Berlin

7 March 2005 21EP 8.2: DPG, Berlin

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)