You should always set manual focus and for most aerial shots this will be set at infinity however the problem you are experiencing when panning etc is more likely to be due to the compression used in AVCHD recordings. The critical issue is how much of the frame changes between frames (ie when panning), because AVCHD uses a keyframe-based compression. That means that it records full image information (albeit still compressed) only every so often, and in between these "key frames," only frame to frame differences are recorded. It furthermore limits the recording to particular data rate (variable up to 35Mbits/second for example), so if there's a lot of change happening between frames, a lot of data can get thrown out. On the other hand, if most of the image is the stationary, with only a small subject in motion, detail remains pretty good all over. The various hacks that allow higher constant bit rates reduce this effect however the GH2 will revert back to the factory variable bit rate when the HDMI is connected for video monitoring. The GH3 is somewhat better in this regard as it will record at high bit rates even with hdmi connected and .mov will also fair better than avchd, motion detail will still reduce with more image detail in moving shots, do a fast pan and you will see the detail reduce.
