I would assume, in the Lois and Clark world, that Superman can be picked up on radar. In Dead Lois Walking, after he's broken Lois out of prison and they're escaping by car, they listen to the radio and hear Jefferson Cole telling the public to look out for the 'mad dog killer' and that Superman is also under suspicion. There's this exchange:

Quote
LOIS
So they're watching the sky, too.

CLARK
I knew they would. It's why we're not flying.
That says to me that radar would detect him.


Wendy smile

Just a fly-by! *waves*