Abstract
We discuss three factors: short range sediment variability, bio-attenuation, and seafloor roughness. In a previous presentation (ASA 2013), we have shown that statistical distributions of bottom loss values derived from measured transmission loss (TL) are nearly invariant to measured sediment properties such as sound speed, density, and porosity. To test if this surprising result was caused by under-sampling of sediment cores, three TL runs were done in 2014 when cores were collected at 1 km intervals. The results of these showing short range variations will be discussed. Among the stations in our HFBL database we have found possible evidence for bio-attenuation due to fish (anchovies) swim bladder resonance (Diachok-Wales, JASA 2005). Finite element modeling of a TL station has shown that seafloor roughness can explain the observed frequency dependence of HFBL values (Isakson, report to NAVO). All these will be discussed.
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