One thing that gave me pause is calling this "coherent noise". I'm used to "coherency" being a property between two different "channels" or sources of signal.

One thing that gave me pause is calling this "coherent noise". I'm used to "coherency" being a property between two different "channels" or sources of signal. Here, I guess it is being used to mean coherency between the X and Y dimensions. Is that right? If so, I think this is not truly coherent noise but rather mimicry. We see large "patches" in X-Y because the 1/f increases the relative power in lower frequency. It is thus a "natural accident" to have low frequency in X and Y form some patches somewhere. But, it's not a coherent effect. I'd be curious to learn if I'm misunderstanding the use of the term.