The above determination is a weak function of the assumed Doppler shift,
which depends on the corotation velocity and the electron temperature.
How far do the uncertainties on these parameters affect the determination
of the 
?
The relative uncertainty
due to the Doppler shift at a given frequency f is
where 
. In the outer torus, the corotation velocity
slightly lags strict corotation [Hill, 1980]. With
large parameter ranges bracketing the expected values, 100 km/s 
120 km/s
and 
K 
K, we obtain 
. Note
that 
is expected to increase with latitude
[Meyer-Vernet, Moncuquet and Hoang, 1995], so that 0.05 is probably an upper limit. We deduce that
the cold plasma frequency
is determined with a 5% relative accuracy, to which a 3% uncertainty
must be added because of the limited frequency resolution of the receiver.