Hi BOAC,
I agree with notso up to a point. The skylight filter is hopless. Trouble is that the UV is not that much good either, especially at altitude
Although the polariser does exactly as notso states,
I think you will find if you are shooting through multi layered glass you will get terrible moire patterns.
Most of my aerial work is done from around 500ftAGL and I prefer to use no filters whatsoever, I simply correct any colour issues using photoshop.
Any half decent photo editing software will alow you to do this.
Good Shooting !!