The primary diagnostic tool for UVCS will be the resonantly scattered Ly-
profile. Its width is a direct measure of the velocity distribution of neutral
hydrogen atoms along the line of sight. Except at very great heights, this
will be the same as the proton velocity distribution due to rapid charge transfer.
The Ly-
intensity relative to the disk
intensity is primarily sensitive to the velocity of the observed gas away
from the sun, which shifts the absorption profile of coronal 
away from
the chromospheric Ly-
emission profile (doppler dimming). Knowledge of
the electron density from the UVCS White Light Channel, LASCO, or other white light coronagraph is
needed for interpretation of the Ly-
intensity, as well as a knowledge
of the hydrogen neutral fraction.
The next most important diagnostic will be the intensities of O VI 
1032 and 
1037
and their ratio. Close to the sun
these lines are collisionally excited, their ratio is 2:1, and their intensity
is proportional to 
. At greater heights, resonant scattering
of transition region emission begins to dominate, and the line ratio and intensities change.
Because 
1037 is pumped by a nearby C II line, the line ratio is velocity-sensitive
up to about 250 km/s.
The intensity relative to the disk intensity drops as the bulk velocity
increases. Similar methods can be used with the Mg X and Si XII doublets.
Third, UVCS will measure the profile of electron-scattered Ly-
. Its width determines
the electon temperature, 
.
Other spectral lines will also be important, particularly [Fe XII] 
1242.
This will be combined with the other strong lines and occasionally with fainter
lines such as Ly-
, He II 
1085, and O V 
630 to determine
the electron temperature and elemental abundances.