  We present the reconstruction of neutrino flavor ratios at astrophysical
sources. For distinguishing the pion source and the muon-damped source to the
3$\sigma$ level, the neutrino flux ratios,
$R\equiv\phi(\nu_\mu)/(\phi(\nu_e)+\phi(\nu_\tau))$ and
$S\equiv\phi(\nu_e)/\phi(\nu_\tau)$, need to be measured in accuracies better
than 10%.
