I've been reading ULB manuals and patents I'm still confused about the ducting of acoustics in the water. I understand that temperature and salinity levels, water surfaces, ocean bottoms, etc. can cause the sound to be refracted, or reflected or whatever; and I keep reading that water will attenuate the ULB pings at roughly 5 to 7 dB per km, depending on depth, salinity, temperature, etc..
Where that attenuation component gets dramatically reduced, is when the acoustic signal gets trapped within a temperature/salinity incline. The spherical component of its radiation is focused within this trap with a far larger component of the radiation able to continue the journey to the point of reception/detection.