There's a bunch of work with sentinel sar sats and a few others tracking marine VHF and radar emissions. I can't go much into the newer efforts though unfortunately.
Thank you for your suggestions! I'm mainly looking at how we can use AIS data to gain knowledge about the maritime domain, with an emphasis on fisheries in the north (norwegian sea and the rest of the arctic) , but as there is so many interesting cases here I constantly go down side paths admittedly, especially if you pull in things like operations research and the newer advances of deep learning.