These shots do show the nice forms of the dunes, and the 2nd shot gives us a nice look at the ripples. Considering the conditions, you got nice results. I studied these two for a while to see what it was that seemed slightly compositionally 'off' to my eye. The two things I came up with are the leading lines taking my eye out of the pic - mid bottom in the first pic, and mid left in the 2nd - and the slight busy nature of the first shot. Those are small points, of course, but when your photography is at a high level, a few nit-pick points might be useful.