The Background Noise Environment During the 2013 Target and REverberation eXperiment

Abstract

This paper presents an analysis of the time- and frequency-domain properties of a multiday series of background noise during the Target and REverberation eXperiment (TREX13) that took place off the coast of Panama City, FL, USA. Background noise was measured at two locations approximately 5 and 6 km south-east of the location of the R/V Sharp where monostatic reverberation was measured. The median spectral density level estimated for a frequency band centered at 2.7 kHz with a bandwidth of 1800 Hz was comparable to the median level at 3.5 kHz averaged over a bandwidth of 100 Hz; both were estimated to be 60 dB re 1 $\mu$ Pa $^2$ /Hz when averaged during the day or night. In contrast, the level at 4.5 kHz, estimated by averaging over a bandwidth of 100 Hz, increased by 14 dB at night. While the data suggest a degree of consistency in the background environment for the purposes of modeling, when assessing levels in the 80–8000 Hz frequency band, time of day was found to be influential. The median spectral levels presented may be used to assess the influence of background noise at a given time of day. Biological noise likely from fish was revealed to be a significant contributor to background noise at night, and daytime background noise levels were primarily influenced by wind.