  Umbral flashes are periodic brightness increases routinely observed in the
core of chromospheric lines within sunspot umbrae and are attributed to
propagating shock fronts. In this work we quantify the shock heating energy of
these umbral flashes using observations in the near infrared He I triplet
obtained on 2014 December 7 with the SpectroPolarimetric Imager for the
Energetic Sun (SPIES), which is a novel integral field unit spectrograph at the
Dunn Solar Telescope. We determine the shock properties (the Mach number and
the propagation speed) by fitting the measured He I spectral profiles with a
theoretical radiative transfer model consisting of two constant property
atmospheric slabs whose temperatures and macroscopic velocities are constrained
by the Rankine-Hugoniot relations. From the Mach number, the shock heating
energy per unit mass of plasma is derived to be 2 x 10^{10} erg g^{-1}, which
is insufficient to maintain the umbral chromosphere. In addition, we find that
the shocks propagate upward with the sound speed and the Mach number does not
depend on the temperature upstream of the shocks. The latter may imply
suppression of the amplification of the Mach number due to energy loss of the
shocks.
