Did Denethor see Frodo captured in the Palantir?

[Inziladun]

Originally Posted by shadowfax

Did Sauron actually know that Aragorn had captured the Corsair ships?

I think Sauron did not know. His attention seems to have been so focused on Minas Tirith that he was blind to all else. He knew of Aragorn, of course, but he would have been forgiven for naturally assuming Aragorn would immediately head for Minas Tirith to rally forces against him.