48 G.M.R. Manzella and MFS-VOS Group
45' N;=:====;=
4D'N
35' N
30' N
O'
lD'E
2O'E
3O'E
Fig.3.4 MFS-VOS tracks during the period September 1999 - May 2000.
strateg ies and software for MFS-VOS. Instead of transmitting a unique message
containing position and data, it was decided to transmit two messages of 512 bits,
the tirst containing a series of positions from which the one corresponding to the
XBT launch can be calculated by interpolation, the second containing the launch
time and data. The old ARGOS software was able to select up to 15 signiticant
points ofaXBT profile, and each temperature value point was constituted by 8
bits. The new software was calculating always 15 significant points from surface
up to 460 m. The surface temperature va1ue was coded in 9 bits. The other points
were calculated as difference with respect to the previous value. In this way it was
possible to code this difference with 7 bits. A CRC, a software check, was added in
order to check the accuracy ofthe entire message. A certain care was taken in order
to avoid the rounding errors. Table 3.3 provide a comparison between the accuracy
of the new code with respect to the previous one.
ARGOS transmission
Old software MFS-VOS software
Depth accuracy (O - 20Om)
2m
lm
Depth accuracy (below 20Om)
2m
2m
Time
2min48sec
2min
Sea surface temperature
0.1333°e
O.I°e
Temperature
0.1333°e
0.1 °e
Table 3.3 Comparison between the previous ARGOS software and the one developed for
MFS-VOS.