@iDew
thanks... i tried to get the depth clearer by improving the lower part of the dunes, i must admit that i tried to add the lightest color before, but it either gets too jaggy or too detailed to the point that it seems like ground, and not relief anymore.

As for the scene, i thought of a connection that might seem convincing when making the piece. It can be abandoned there in the desert, because as i said: something went very wrong with it. The machine just doesn't gather as it's meant to do so people threw it in a desert 'cause no one could deactivate it properly.

But again, 'twas just something i thought when making that piece, in the end it's just there because i wanted to, no special motive whatsoever, i imagined the scene that way. 
 

I really liked this piece overall, But there are few things that were disturbing my eye:

1. The depth of the dunes is not clear enough. I suggest adding the lightest moon color to some of the "lightest" dunes.

2. The perspective is a bit strange, try to improve the lower part of the dunes.

3. It's like the bot is just standing there without any connection to the scene. What is it trying to gather when he looks to that way?

But again, overall, I think you did a very good piece, the dithering here is done nicely and the use of only these 4 colors from the challenge is amazing. I also liked the clouds very much.

Good luck in the challenge :)