Aerodynamik
However, at the risk of repeating myself, it is the experience that the observer brings along that counts.
You are repeating yourself and quite needlessly, we've already established that:
a) Civvies bring different skills and experience
b) Some (by far the minority) very experienced officers do not make good air observers
To be honest I don't think that civvies recruited directly is a great idea, some relevant experience in a policing role is vital.
And, believe me, a 500hr PPL could not do a perfectly good job they would spend most of their time concentrating on the fact that their brains were screaming in abject terror and trying to find a way out of their heads - especially at night and/or in poor wx.
Zorab
I concur completely with Zorba
They're clearly just doing it to wind you up, now.