Above map provides an overview of groundbased tracking stations in the ESA ESTRACK and the US AFSCN network that are near or on the final trajectory of UARS. For relevant trackings tations, times of Advance of Sight (AOS) or Loss of Sight (LOS) are indicated. UARS is depicted at the point of reentry (see previous post) as indicated by SSC.
From the NASA talk by Johnson, they pinpointed the 04:00 +/- 1 minute UTC time and 14.1 S, 170.2 W location of UARS's demise using detections and non-detections by "a number of sensors".
As can be seen on the map, none of the regular tracking stations had direct coverage of the reported reentry location, begging the question where the "large number of detections" NASA's Johnson was talking about comes from. UARS could first have shown up at the Kaena Point tracking facility in Hawaii at 4:07 UTC. At that time, it would have been without groundbased tracking for quite some time already (over half an orbit).
Of course, we cannot exclude that a temporary tracking facility (e.g. an AEGIS ship) was employed in Polynesia at the time, providing additional data.
Also, a reader of this blog wrote to me with the suggestion that the US Navy's sensitive network of hydrophones could have picked up a signal when wreckage hit sea surface. I have no idea how feasible that is.
I still feel space-based observations were possibly involved (see my earlier post here), but are not being publicly acknowledged. The early warning satellites DSP F20, DSP F16 and SBIRS Geo-1 would have had coverage of the reentry location.
(note added: if anyone knows of additional tracking stations along the trajectory, info is welcome)
Note added 29 Sept 2011
Dan Fischer raised the option in the comments that Infrasound detections could be involved. Indeed, this is a possibility (I consulted a Dutch infrasound researcher for an opinion here, and he thinks it is feasible, especially if sonic booms were involved) even though the distances to infrasound arrays involved are large.
A number of infrasound arrays are scattered over the Pacific area, listening for possible atomic detonations in breach of the Nuclear Test Ban treaty. A map of them can be found here. In the wider area, such arrays are located on Tahiti (French Polynesia), Hawaii, the Marquesas and New Caledonia. The UARS reentry location is within this triangular area. Below is a map of infrasound detection arrays located in the Pacific around the published UARS reentry location.
Edit late 29 Sept: Dutch infrasound researcher Läslo Evers just notified me he has checked the Tahiti and New Caledonia infrasound records for the reentry - he finds no sign of it.