Although sound travels better in a moist atmosphere, fog is to dense so absorbs sounds, especially high pitched sounds.

I have lived by the sea all my life and within hearing distance of foghorns including the Portsmouth harbour entrance marker horn and the Bristol Channel navigation horn which can be heard at 46 mile minimum distance. Just because it is foggy it does mean it is relatively quiet, the sound is absorbed so it is perceived as being quieter, the foghorn has to be able to cut through that effect.

If you read the article and other articles about sound waves you will understand that long soundwaves travel around and often through obstacles far better than short soundwaves this point to the fact that low frequency sound is less disturbed and distorted by the environment than high frequency sound allowing it to travel further. This can be heard on wide band radio.

I recognise that to produce low frequency sound you need a larger chamber than high frequency sound. My point is manufacturers are kidding themselves by making louder whistles with higher frequency sounds instead of increasing the efficiency of lower frequency whistles. The fact is the manufactures are going against hard scientific fact and misleading people with their sales pitch in the process.

My original post was reflecting on why manufacturers feel the need to do this. the reason is the average person does not understand the process of sound so they perceive that a loud high pitched ear bleeding sound is more effective when they blow a whistle than one with a lower pitched sound, using our own failings in hearing to mislead use, probably through the lack of understanding, of which is the best sound.

A well researched and engineered whistle at 70dB would be far better than one at 105dB. This is borne out by the human voice compared to the storm whistle.