In the movie "First contact", near the end:
We see Cochrane, Riker and Laforge in "The Phoenix" for humanity's first warp drive launch. This action will lead to first contact with the Vulcans, who are passing through the sector at the moment the warp drive engages. The Vulcans detect the warp drive signature and decide that it is time for them to visit Earth. Just before engaging the warp drive, Data, inside the Enterprise, fires 3 photon torpedoes at the Phoenix, but misses it, which causes confusion among the Borg. Then, The Phoenix engages the warp drive and comes back to Earth the same way. A moment later, we see the Vulcan ship landing on Earth at the Phoenix launch site.
How come the Vulcans were not able to detect:
1- The photon torpedo launch seconds before the warp drive?
2- The enormous Enterprise E orbiting Earth at their arrival?