The Question and Answer section for Robert Browning: Poems is a great resource to ask questions, find answers, and discuss the novel.
The speaker describes the long barren landscape as a "grey sea". I think this speaks to the mood and texture to the poem. There is a sense of emptiness to this.
I'm not sure what poem you are referring to and what your question is.
We see the dimly lit imagery of sea, the moon, sand and light reflection in this poem. It is very peaceful and almost surreal.