Its AUC,
Late channel from my understanding are the EM responses that occur after a certain period of time. Actually I had a look and couldn't find a good explaination of it, they are "late" but "late" compared to what... the "early" ones :-)
Articles just seem to refer to them as "early", "late" or just as numbers 1-9, 20-28....
It some sort of weird geophysics lingo.
