Shooting through perspex

Tried a couple of shots through a perspex screen with the result shown. Is there a way to counteract the artifacts shown on the photo ?

perhaps a polarising filter although that wont take out the inevitable dirt and scratches. If it did work of course it wont help after the event.

I did wonder about that Ken. I don't know why they need a perspex screen as high as it is. A 4ft screen topped with wire mesh, big enough to poke a lens through but small enough to stop a child climbing through would have been ideal.