this is great!! i didn't think tha author would put physics thought into this! especially tele-com side.
so basically visible spectrum for dragon's eyes is wider than human's right? it's not wrong that wind dragon say "watching us using light" because basically there is two radio frequencies emited, first is lower frequency (usually few hundreds MHz) to detect any objects in range, second is microwave frequency (few GHz) to track specific object detected by first frequency, this second frequency is emited 'pointedly' to that specific object, while first frequency is emited to 'all direction'. so it's right way to say 'watched' rather than 'detected', if we only use lower frequency, they will be just 'detected'. but... i wonder if that dragon's eyes were alright, cuz EM emmited by radar is usually have a large energy density... i wonder if that dragon saw a very bright light from the ship.
you may see in movies, that radar antenna is spinning, that use lower frequencies! while in some movies you may see the antenna is tracking plane, that is when the radar using microwave freq! what's collected from radar (this is my thought): range, object's speed, object's direction, object's size
well i'm still studying, so my explanation may incorect. well my point is that visible spectrum for dragon is wider than human's