PDS_VERSION_ID        = PDS3
LABEL_REVISION_NOTE   = "VERSION 2, RDR+Project Team, 2006-07-17"
RECORD_TYPE           = STREAM

OBJECT                = TEXT
  INTERCHANGE_FORMAT  = ASCII
  PUBLICATION_DATE    = 2006-03-01
  NOTE                = ""
END_OBJECT            = TEXT
END

This dataset contains data from the Huygens Doppler Wind Experiment (DWE) 
obtained during the Huygens Mission at Titan.

In addition to the data themselves, the datasets contain a wide variety of 
supporting files and documentation for the Archive user.
The data set has been organized in six principal directories one level below
the root:
DOCUMENT, INDEX, DATA, GEOMETRY, CALIB, CATALOG.

Caveat
======

(A) The Huygens trajectory

The knowledge of the Huygens trajectory is of primary importance for the
payload data analysis.
The official trajectory reconstruction is the result of a common effort; 
it is produced from a subset of the Huygens experiments and housekeeping data 
by the Huygens Descent Trajectory Working Group (DTWG). The DTWG input files  
and the derived trajectory is archived within the Huygens DTWG data set. 
The Huygens Probe auxiliary data ((e.g. aerodynamic coefficients, 
Probe physical properties, parachute characteristics) are archived 
within the Huygens housekeeping (HK) data set. 
Warnings: It should be pointed out that the reconstruction 
of descent trajectory of the Huygens probe is not coherent with 
the altitude profile retrieved from the Huygens radar altimeter. 
Different approaches/methods for descent trajectory reconstruction 
resulted in altitude and velocity profiles that show discrepancy, 
not consistent with uncertainty range relevant to models and measurements. 
The reason for this discrepancy is at present still under investigation. 
Results of future analysis could imply the need to reconsolidate the 
trajectory. 

(B) Time information

Any user of the Huygens data must be aware of the following:
1. The T0 time, official start of the descent, is known with
an accuracy of 0.125 seconds. 
Its official UTC value is 2005-014T09:10:20.828 .
2. Time can be displayed differently from one Huygens data 
set to another, as shown in the two tables a) and b).
Time units SEC, MSEC and HH:MM:SEC indicate that the time 
is given w.r.t. T0, whereas UTC indicates that it is independent 
from the precise value of T0.


a)
===================================================================================
Huygens data set                                      | ACP | GCMS |SSP | HASI    |
Time unit in the data products                        | UTC | UTC  |SEC | MSEC    |
Time unit for the keyword START_TIME                  | UTC | UTC  |UTC | UTC     |
Time unit for the keyword SPACECRAFT_CLOCK_START_COUNT| MSEC| MSEC |SEC |HH:MM:SEC|
Time unit for the keyword NATIVE_START_TIME           | SEC | SEC  |SEC | MSEC    |
===================================================================================

b)
===================================================================================
Huygens data set                                      | DISR| DWE  |HK  | DTWG    |
Time unit in the data products                        | N/A | UTC  |UTC | UTC     |
Time unit for the keyword START_TIME                  | UTC | UTC  |UTC | UTC     |
Time unit for the keyword SPACECRAFT_CLOCK_START_COUNT| SEC | N/A  |SEC | N/A     |
Time unit for the keyword NATIVE_START_TIME           | N/A | N/A  |SEC | N/A     |
===================================================================================


For more information about the data please contact the PI team:

        c/o Dr. Michael K. Bird
        Argelander-Institut fuer Astronomie der Universitaet Bonn
        Abteilung Radioastronomie
        Auf dem Huegel 71
        D-53121 Bonn, Germany
        mbird@astro.uni-bonn.de

For further information about the dataset and about the PDS please 
contact the Atmospheres Node of the Planetary Data System:

        Lyle Huber
        NASA PDS
        New Mexico State University
        Las Cruces, USA
        lhuber@nmsu.edu

For more information about the dataset and about the ESA Planetary 
Science Archive please contact the European Space Agency at the 
European Research and Technology Center (ESTEC), Noordwijk, The Netherlands:

        Olivier Witasse
        ESTEC/ESA
        owitasse@rssd.esa.int