Dynamic Ambient Noise Model (DANM) Evaluation Using Port Everglades Data
NAVAL RESEARCH LAB STENNIS SPACE CENTER MS ACOUSTIC SIMULATION SECTION
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Measured omnidirectional noise at a shallow water site near Port Everglades and radar tracks for local ships were used to evaluate a new ambient noise model, the Dynamic Ambient Noise Model DANM, developed for use on board Navy systems. For four consecutive days of data, the daily means of the modeled noise levels were higher than the data. The most likely cause of mismatch was two factors associated with the ship sources. The first was the relative assignments of ship classes to the radar track vessels for input to the model. The vessels were assigned classes by speed with no means to discriminate between large vessels traveling at low speeds and recreational vessels that do not contribute significantly to the noise field. The second factor was the source level model within DANM, which is implemented with no speed dependence. A dependence was introduced into the model through the ships class assignments, but would be more properly implemented within the model itself, and may be necessary for accurate predictions near a port. The lack of speed-dependent source levels and the source level curves themselves may be the causes of the frequency dependence seen in the modelmeasurement mismatch. Model predictions with all radar vessels assigned to the minimum source level resulted in lower but better modelmeasurement agreement. This spread of about 10 dB in daily means with different source level assignments confirms that source level assignments for dynamic shipping are critical to accurate model predictions. There was frequency dependence to the mismatch, with the model matching better at higher frequencies. Shear propagation is unaccounted for in the propagation models used by DANM and is a likely source of error for this environment at the lower frequencies.
- Physical and Dynamic Oceanography
- Marine Engineering