In support of monitoring technologies to evaluate the potential environmental effects of offshore energy devices, this project attempts to ultimately improve upon traditional acoustic sensing techniques by developing a cost-effective compact array of acoustic vector sensors that characterizes, classifies, and provides accurate location information for anthropogenic and natural sounds. The NoiseSpotter consists of three acoustic vector sensors arranged in a three-dimensional array deployed as a seafloor mooring. Each vector sensor measures acoustic pressure and the three-dimensional particle velocity vector associated with the propagation of an acoustic wave, thereby inherently providing bearing information to an underwater source of sound. Here, performance characteristics of the NoiseSpotter are presented, along with an analysis of its abilities as an operational passive acoustic monitoring system to characterize sources of sound. Data are presented from controlled acoustic transmissions in a quiet environment and an energetic tidal channel in the presence of non-acoustic flow noise. NoiseSpotter performance is demonstrated through its modular design, ease of deployment/recovery, ability to remove signal contamination by flow noise and the ability to geolocate acoustic sources of interest.