This paper reports high-accuracy measurements of geocoronal Balmer alp
ha line profiles and demonstrates that the profiles are well fit with
a model which includes cascade excitation by solar Lyman series radiat
ion from n > 3 in addition to the direct excitation of n = 3 by solar
Lyman beta. The increase in the signal-to-noise of our data is made po
ssible by the use of the Fabry-Perot annular summing technique impleme
nted at our Fabry-Perot facility at the University of Wisconsin's Pine
Bluff Observatory. The new sensitivity has allowed us to make a detai
led examination of line profile asymmetries and to conclude that they
are compatible with predictions that of the order of 10% of the geocor
onal Balmer alpha emission is caused by the cascade process. Cascade e
xcitation alters the observed profile because it produces Balmer alpha
emission along fine structure paths yielding slightly shifted wavelen
gths not present in direct Lyman beta excitation, which is the predomi
nant excitation mechanism for geocoronal Balmer alpha. We discuss how
fine structure excitation affects studies of non-Maxwellian exospheric
hydrogen velocity distributions and effective temperatures through Ba
lmer alpha line profile measurements. In a broader context, we conside
r how inclusion of the cascade excited emission in future radiation mo
dels can enhance their accuracy and their potential for assisting in t
he isolation in the data of shorter-term solar geophysical effects and
longer timescale changes in exospheric hydrogen densities.