Here we used the basic spreading loss acoustic models and a semi empirical shallow water model known as Colossus for transmission loss predictions and compared with in situ measurements of explosions originated from underwater rock blasting activities performed in shallow waters of a coastal bay area in Brazil. Sound propagation in shallow waters can have great variability due to many different characteristics of these environments and its described by numerous interactions with both the sea surface and sea floor which influence the propagation of acoustic energy through reflection, scattering and absorption.
#Define colossus series
This study is the first of a series designed to obtain accurate information on underwater noise pollution and its potential impact on biodiversity in the Port of Cartagena. The loading of cargo containers was identified as the main source of impulse noise. A GIS map was drawn up with the spatiotemporal distribution of the basal sound pressure levels by coupling the acoustic data with the vessel’s GPS positions to identify the sources of the impulsive noise of interest and their temporal characteristics. An autonomous vessel was equipped with a smart digital hydrophone with a working frequency range between 10 and 200 kHz and a received voltage response (RVR) of, approximately, −170 dB re 1V/µPa. This paper describes the method used and results of the spatial monitoring of both the baseline noise level and the impulsive noise sources in the Port of Cartagena. Recording underwater impulsive noise data is an important aspect of mitigating its environmental impact and improving maritime environmental management systems. The reflection coefficients are calculated from the Morse- Mackenzie relations for loss per bounce. The M-S model is also extended to treat arbitrary negative and bilinear sound-speed gradients by using new general expressions for skip distance, near-field anomaly, and reflection coefficients. The M-S model is compared with Rogers' semiempirical model based on numerical calculations of the normal-mode solutions to the wave equation for propagation in shallow water. The M-S model yields good predictions when applied properly it is not to be used for all environments. The chief criticisms of the model have been that it could not be adjusted for arbitrary negative sound-speed gradients, and that it uses empirical bottom loss values.
#Define colossus free
With a few free parameters, including water depth, about 100,000 measurements from 100 Hz to 10 kHz were fitted within stated error bounds. The M-S model, a semiempirical model based on extensive measurements taken off the Atlantic Coast, uses several concepts (1) refractive cycle, or skip distance (2) deflection of energy into the bottom at high angles by scattering from the sea surface and (3) a simplified Rayleigh two-fluid model of the bottom for sand or mud sediments. This report reviews the Marsh-Schulkin (M-S), or Colossus, model of acoustic transmission loss in shallow water in light of new information and techniques that have emerged since its introduction in 1962.
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