Melvyn Mason: radio buoys and explosions at sea

Electronics technician Melvyn Mason describes the use of radio sonobuoys in the 1960s for seismic refraction studies at sea, central to the revelation of plate tectonics.

I'm Mel Mason, I'm an electronics technician and I joined the Department in 1966 as part of setting up a new development team, or an increased development team - especially with electronic instrumentation for geophyscial instruments for the department. Seismic refraction at sea is a system whereby we use sound waves to determine a rock velocity, sound velocity of a rock. This allows scientists to determine the sort of rock that lies beneath the crust. The way that it is done is that you let off a large explosion to produce a sound source. That sound then travels through the sea but also is refracted into the rock layers. And the speed at which this sound travels through the rock layers gives the scientists an idea of the type of rock that it is. And the signals are detected by hydrophones suspended beneath sonobuoys, which are then sent back to the ship via a radio signal but also internally recorded when the buoys are out of radio range. 

Here we have the buoy ready for deployment: the aerial has been attached, the navigation light has been fitted and the hydrophone will be attached to this connector here. The buoy electronics itself attached underneath this plate here is bolted onto the buoy with a single 'O' ring seal to make it waterproof. below the buoy would be a pole of similar length to the aerial with a lead weight to stabilise the buoy to keep it in the upright position. This is the lifting strop which we use for recovery, attached to this would be what we call a stray line with floats that allow you to grab it, attach this to a lifting crane to haul it out of the water on retrieval. This buoy is number 4, which means that it's channel number 4 on the radio receiver. 

Here we have the ship recorder, these are the clock traces form the ship clock up here, this is the hull geophone detecting the shock instant and you'll see in a minute that we start to get groundwaves received from the sonobuoys, from these two traces here. It takes some time but here they come, and then this is the direct wave of travelling through the water.

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