"So Noah awoke from his wine, and knew what his younger son had done to him" (Genesis 9:24).
An illicit sexual act is
indicated. While Noah was drunk, he had no idea what was occurring

The situation begins with Noah becoming drunk and being violated

The perpetrator, Canaan, is named in verse 22 as Ham's son

Ham was the first on the scene after his son's perverse act, guessed what had happened, and reported it to his brothers to seek counsel about what they should do. Later, when Noah awakes, there is no doubt in his mind that Canaan had defiled him, and he curses him for it.