  As new techniques exploiting the Earth's ambient seismic noise field are
developed and applied, such as for the observation of temporal changes in
seismic velocity structure, it is crucial to quantify the precision with which
wave-type measurements can be made. This work uses array data at the Homestake
mine in Lead, South Dakota and an array at Sweetwater, Texas to consider two
aspects that control this precision: the types of seismic wave contributing to
the ambient noise field at microseism frequencies and the effect of array
geometry. Both are quantified using measurements of wavefield coherence between
stations in combination with Wiener filters. We find a strong seasonal change
between body-wave and surface-wave content. Regarding the inclusion of
underground stations, we quantify the lower limit to which the ambient noise
field can be characterized and reproduced; the applications of the Wiener
filters are about 4 times more successful in reproducing ambient noise
waveforms when underground stations are included in the array, resulting in
predictions of seismic timeseries with less than a 1\% residual, and are
ultimately limited by the geometry and aperture of the array, as well as by
temporal variations in the seismic field. We discuss the implications of these
results for the geophysics community performing ambient seismic noise studies,
as well as for the cancellation of seismic Newtonian gravity noise in
ground-based, sub-Hz, gravitational-wave detectors.
