A review of low-frequency (LF) (20–200 Hz) physical noise models and measurements shows long-term persistent directional characteristics associated with distant shipping lanes and density patterns. Short-term averages show a temporally dynamic field composed of resolved distant shipping and uncorrelated background noise. These results emphasize the importance of the coherent contribution from coastal shipping to the midocean noise field. Vertical directionality measurements, such as those by Anderson et al. [Technical note 800, Naval Ocean Systems Center, San Diego, CA (1972)] show a broad angular distribution of noise intensity near the horizontal at low frequencies and a peaked distribution about the horizontal at high frequencies. This broad angular distribution near the horizontal is consistent with sound propagating downslope by means of a bottom reflectivity which favors lower frequencies. Since the frequency variation of the noise intensity near the horizontal was found smooth for basins with diverse geographic locations and variable populations of ships, then, in addition to surface ships, environmental noise such as wind driven noise may influence the vertical directionality.