Probably Bristow (sorry - I replied to an old page so didn't see the response!) I'd guess from his location, but those figures are standard North Sea figures as you will see from this link:
http://www.helidecks.org/download%20...0p%20r%20h.pdf
To the best of my knowledge, the various values are empirically based and not as a result of formal 'SHOLs type' trials. The future trend in the North Sea is to move away from P/R/H figures and towards a more useful measurement of total motion severity.