We propose a method for estimating the reflection coefficient of a subvertical boundary and the the quality factor of the medium between a receiver and the subvertical boundary. The method uses surface waves from transient deterministic sources and is inspired by the occurrence of non-physical arrivals in seismic-interferometry results due to intrinsic losses in the medium. The quality-factor estimation with our method can be used as an alternative to and confirmation of results from the spectral-ratio method. We demonstrate our method on data from ultrasonic laboratory measurements.