try picking points on the horizon to track. you will also need to track for rotation to level out the horizon. try to pick points that are reasonably far appart, but stay within the frame for the duration that you need to track.
once you stablilize the shot, you will need to re-introduce smooth horizontal movement of the camera as it passes over the land.
i took a stab at it, and in a few minutes found two decent points just below the horizon. i tracked position and rotation and got ok results and applied directly to the footage.
then just scaled the footage up about 5%, added motion tile to expand the footage a bit (mirror edges checked) and parented to a null.
i rotated the null slightly to level out the horizon and then keyframed the null position to bring the pan back into the shot.
you can try to enabling frame blending (frame mix) for the footage to help smooth some of the jumpy pixels a bit... it will have a more dramatic effect if the original footage is interlaced (it looks progressive, but it is hard to tell once it is scaled).