The meaning of SWALE and SWOOPED INTO SOFTER VISION

The passage below is from Fathoms: The World in the Whale Hardcover by Rebecca Giggs.

A group of us slept lightly in the dunes, arrayed like question-marks and commas on the white sand. Our minds cast to the cetacean huffing beyond the swale, then swooped into softer visions. The sounds of surfers arriving in the dark woke me. I brushed a pearly skin of sand off my cheek, my shoulder, one thigh.

In this US and I are volunteers who wants to help save a stranded whale. What I want to ask is the meaning of the 2nd sentence.

Here the volunteers took a light sleep, and in their sleep their mind first goes to the whale’s huffing coming beyond the swale, a narrow depression.

Do I read right?

And then their mind was quickly taken back into softer, that is, less harshy visions. Here visions seems to mean mental image.

In bold faced part, does my interpretation make sense?

If not can you give me a better one?

Thanks a lot.