![enter image description here](https://i.stack.imgur.com/gCOwu.jpg)

I am currently at my brother's graduation ceremony at Adelaide University, and in the Professor's/Post-grad seating area, sits a man fully in green. What does this special gown mean?

(Apologies for the awful picture)![enter image description here](https://i.stack.imgur.com/AaI6e.jpg)