More pictures of hydrophone work

Twenty five years separates these two photographs. On the left, Mr Isaac S. Blonder is pictured in 1975 with an array of equipment attached to hydrophones. In an intriguing experiment, underwater sounds from a variety of marine organisms were played through underwater loudspeakers, while another machine waited to record any response. That response itself would then be played back into the water, in the hope that any animal in Loch Ness would interpret its own vocalisations as a challenge. The oars remained at the ready!

On the right, in 2000, a digital recording of ambient noise is being made as part of a series of background noise recordings. If any unusual acoustic signals are recorded on the underwater camera unit one mile (1.6 km) away, they will be compared with these data.

"Take one of me, Ike!"   Dick Raynor at the other end of the boat, apparently ready to walk home if necessary... Listening to underwater sounds in Loch Ness is complicated by the reception of noise from nearby communications systems. In 1975 we recorded what were at first interpreted as the sounds of "mating crustaceans",( - that is "crust"aceans, not "cet"aceans -) but later transpired to be teleprinter noise from the CANTAB trans-atlantic cable which runs close by. In many locations,  noise is a problem when using long hydrophone cables. The operators hope that by going "deep" they will avoid surface noise, but the long cable acts as an antenna for both electro-magnetic and mechanical signals. There is more about Ike Blonder at