  Protostellar outflows provide a means to probe the accretion process of
forming stars and their ability to inject energy into their surroundings.
However, conclusions based on outflow observations depend upon the degree of
accuracy with which their properties can be estimated. We examine the quality
of Atacama Large Millimeter/submillimeter Array (ALMA) observations of
protostellar outflows by producing synthetic $^{12}$CO(1-0) and $^{13}$CO(1-0)
observations of numerical simulations. We use various ALMA configurations,
observational parameters, and outflow inclinations to assess how accurately
different assumptions and setups can recover underlying properties. We find
that more compact arrays and longer observing times can improve the mass and
momentum recovery by a factor of two. During the first $\sim$0.3 Myr of
evolution, $^{12}$CO(1-0) is optically thick, even for velocities $|v|\ge 1$ km
s$^{-1}$, and outflow mass is severely underestimated without an optical depth
correction. Likewise, $^{13}$CO(1-0) is optically thick during the first
$\simeq 0.1$ Myr. However, underestimation due to shorter observing time,
missing flux, and optical depth are partially offset by the assumption of local
thermodynamic equilibrium and higher excitation temperatures. Overall, we
expect that full ALMA $^{13}$CO(1-0) observations of protostellar sources
within 500 pc with observing times $\gtrsim 1$ hrs and assumed excitation
temperatures of $T<20$K will reliably measure mass and line-of-sight momentum
to within 20\%.

Solar and Stellar Astrophysics