it's unreal engine 2, which you'd think would mean there was something for that, but people are generally only interested in models generally, not maps, so there's no tools for this, and every ue2 game seems to differ just enough to make its sdk useless for getting anything out of another ue2 game. best bet seems to be something like "ninja ripper" but i have had pretty shit results with that so far (that's the "just rip whatever the fuck i am rendering right now" stuff and has all the problems you would expect plus exciting ones you would not expect).
splinter cell 3 does actually have a level editor but that's for the multiplayer, which is actually a separate game, and doesn't help with the cooked singleplayer maps
someone leak me the splinter cell 3 dev repo