aareadme.txt for cassini

This directory holds annual ASCII files of Cassini cruise phase
1-minute-averaged magnetic field data taken during the interval
between mid-1999 when near-continuous magnetic field observations
were begun and the mid-2004 insertion of Cassini into Saturn
orbit.  There are no planetary encounter data included.  The
data are in RTN coordinates.  

The data are mostly from the fluxgate magnetometer (FGM). The table
at vhm.txt identifies the 52 days in 2000-2004 for which the data are 
solely from the vector helium magnetometer (VHM).  Days not in the 
table contain only FGM data.

The data were produced from raw (L1A) data at the PDS/PPI node using 
software provided by the Cassini MAG team, and employing the latest 
calibration available.  PDS/PPI produced both 1-sec vectors and 1-min 
averages.  The MAG team reports that while range-0 data are well 
calibrated for both FGM and VHM, higher range data need improvement.  
See
http://www.igpp.ucla.edu/cgi-bin/ditdos?volume=COMAG_0XXX&folder=DOCUMENT/DATA_QUALITY&file=RANGE_CHANGES
for details.  In particular, this documentation reports that FGM was
in range=0 for the following extended intervals (plus other brief intervals):

1999/230/05 - 1999/245/07 (YYYY/DDD/HH, inclusive)
1999/245/09 - 2000/037/12
2000/039/00 - 2000/053/18
2000/053/20 - 2000/056/01
2000/057/23 - 2002/334/13
2002/334/17 - 2003/292/18
2003/292/22 - 2004/046/11
2004/046/15 - 2004/088/08
2004/088/12 - 2004/136/06
2004/136/11 - 2004/174/01
2004/174/06 - 2004/182/17

This directory also contains a PDS Label file that enumerates many
attributes of the data files and the words of the records of the data
files.  This file is called herein fmg_rtn_1m_cruise.lbl
Briefly, the parameters are, in sequence:
Time YYYY DOY HH MM for averages built from MM:00 to (MM+1):00
BR, R component in RTN, nT
BT, T component in RTN, nT
BN, N component in RTN, nT
BTOTAL, Field magnitude, nT
RANGE, Heliocentric radial distance of spacecraft, AU
LATITUDE, Heliocentric latitude of spacecraft, deg.
LONGITUDE, Longitude of spacecraft, East from Sun-Aries line, deg.
X_IHG, Inertial Heliographic X component of sun-to-spacecraft vector, AU
Y_IHG, Inertial Heliographic Y component of sun-to-spacecraft vector, AU
Z_IHG, Inertial Heliographic Z component of sun-to-spacecraft vector, AU
NPTS, number of 1-sec values in 1-min averages

(Note that IHG is what NSSDC/SPDF typically refers to as HGI.)
 
Two changes were made to the PDS/PPI-provided files.
First, PDS time tags of the format YYYY-MM-DDTHH:MM:DD were replaced
by FTPBrowser time tags of the format YYYY DDD HH MM.  Secondly,
minutes with no data had no record in the PDS-provided files but
have records, with all fill values except the time tags, in the 
FTPBrowser version.

An FTPBrowser interface to these data, providing plots and lists
of some or all parameters for arbitrary times is available at
http://omniweb.gsfc.nasa.gov/ftpbrowser/cassini_min.html

The 1-sec data are available from PDS/PPI at http://pds-ppi.igpp.ucla.edu/
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Related data and directories:
SPDF Data and Orbits Services <http://spdf.gsfc.nasa.gov/>

SPDF Contact: Natalia Papitashvili <Natalia.E.Papitashvili@nasa.gov>,


Please acknowledge NASA's Space Physics Data Facility, for data usage.

Authorizing NASA Official: Dr. R.E. McGuire, Head, SPDF, NASA Goddard Space Flight Center
                        301-286-7794, e-mail:  Robert.E.McGuire@nasa.gov
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