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HDDS needs to be updated with the correct attenuation length for the new UPV design that includes wave-shifting fibers and therefore , much less attenuation . In this part of the paper we assume equal efficiency in S and P polarizations ; any common attenuation factor is also dropped if system contrast is the quantity of interest . This data , along with the USAF natural attenuation data from Site 32 , will be used to define the plume and to help document the extent to which biodegradation is occurring . Subsequent analysis revealed a power-law dependence of the effective attenuation coefficients on Z , i.e. dga / dp Zn , where n = 1.25 . However , because a berm is wider than a wall ( thus , requiring more land than a wall when constructed ) and because the 1 to 3 dB ( A ) additional attenuation is , at best , only barely perceptible to the human ear , a berm 's acoustical advantage does not necessarily guarantee its choice versus a wall .