I was going to mention that, actually. Pressure pattern flying involves flying an accurate physical altitude (using a rad alt over the ocean) and using the pressure altimeter to determine the pressure change over a period of time. The pressure change (due to flying through a pressure pattern) can be shown mathematically to relate to the crosswind (not headwind), and thus drift, aircraft has experienced. It's a technique which was used by aircraft for long range over-water navigation, before area navigation systems such as INS/IRS/GPS were developed.
When I was studying it, I was always curious at how they obtained rad alts at high level - or if they simply flew below 5000'. Now I know.
