Application of Monin-Obukhov Similarity Theory to a Near Shore Atmospheric Acoustic Model: A Measurement Informed Evaluation

Abstract

An understanding of sound propagation from industrial activities, airports, wind farms, and a variety of other sources can be assisted by acoustic modeling. Modeling airborne sound propagation over long distances usually requires making a number of assumptions pertaining to the state of the atmosphere and terrain in addition to those in the governing equations and numerical methods. One set of assumptions about the lower atmosphere is Monin-Obukhov Similarity Theory (MOST)–a system used to estimate vertical profiles of air temperature, humidity, and wind speed. In this work, MOST air temperature profiles are compared against long-term air temperature profile measurements up to seven meters in elevation over water and marsh grass surfaces. In addition, the Crank-Nicholson Parabolic Equation (CNPE) method is used to compare acoustic sound pressure level predictions between MOST-informed and air temperature measurement informed sound speed profiles. Applications of MOST meeting the conventional stability parameter condition for validity were found to be roughly as successful over land as over water. However, at night over the marsh, MOST was 35% less likely on average to meet the validity condition whereas over the water it was only 13% less likely. Acoustic model predictions using MOST temperature profiles diverge from those using measured profiles under negative temperature gradients as a result of a sharp increase in the predicted temperature below 1 m in elevation.