Since I am on the agenda for the RAINEX conference call next
Tuesday about expendables, I thought the following message
and graphic may be helpful to decide on how to proceed with
the GPS dropsonde order, i.e., new versus old sondes.  

According to Terry Hock, our Dropsonde Engineer, the new
sondes will provide a much better dataset.
The new sondes contain an improved GPS receiver; winds are 
picked up more quickly after being dropped from the airplane 
and data are received all the way down to the surface of the 
ocean (as shown in the attached graphics).  While the reliability of 
the old sondes was around 85-90%, Terry considers the success rate 
of the new sonde to be close to 100%, eliminating the need for 
calibration.

Terry was also quite certain that EOL would have no problem 
getting 450 of the new sondes from Vaisala if we order the sondes 
no later than end of February.  

Terry will join us on Tuesday for the phone call in case there are 
additional questions.

Brigitte


------------------------------
Many of the electronic parts currently used in the dropsonde are now
obsolete or nearly so.  The usable stock of parts at Vaisala is
quickly diminishing and thus a redesign is necessary.  The other
factor, performance although not a requirement for redesigning the
sonde is an issue because of recent advances in GPS technology. 
Especially in hurricanes, the current GPS dropsonde data sets often
have drop outs in the lowest levels of the profile.  An off the shelf
OEM GPS receiver and antenna built by u-blox has been incorporated
into a Vaisala dropsonde by our engineers.  A small number of these
were dropped by the NOAA Hurricane Hunters during this past year's
hurricane season.  The performance difference between the current
Vaisala dropsonde and a u-blox sonde is quite dramatic (see attached
graphic).  Additionally, Europe is close to realizing their own GPS
satellite configuration called, Galileo.  By some quirk in electronics
this system will render the current Vaisala GPS dropsonde useless. 
This will occur in phases of degradation in data quality starting in
the summer of '05 with total obsolescence by years end.

Vaisala has agreed to incorporate the u-blox solution into their
standard GPS dropsonde product.  As with everything Vaisala does this
comes at a price and that price is roughly $100 per sonde, as stated
above.  Given the dramatic performance payoff and reliability of data
every researcher to date who has seen these data (mostly those at HRD
and the Hurricane Center) have agreed that this is a small price to
pay.