With regard to "Angel One", I can only speculate that the sensors can be tuned to actively scan for the emission spectra of a particular material. Presumably the ship aims a sensor beam at the surface that will reflect off platinum in a distinctive way. This was effective in "Angel One" because there was no native platinum (or, at least, no refined platinum on the surface), so the foreign platinum of the merchant's insignia stood out.
This particular sensing technique would not be useful for detecting ships. Presumably you could send an active pulse that would "light up" materials common in ship hulls, but if the beam has to be fairly focused, you would have little luck finding a ship in all of space. Furthermore, I got the impression in "Survivors" that Worf's failure to detect a ship floating in a Lagrange Point was a sign of incompetence: Picard, Riker, and Worf himself all seemed to think that he should have spotted a ship in such a location.
Furthermore, while the type of scan used to detect platinum in "Angel One" must have been able to detect a small object at a distance of thousands of kilometers, the same technique might not have been so effective at the greater ranges (hundreds of thousands of kilometers) that would likely be required when scanning space for ships.
Starship shielding or other field effects might also interefere with such a scan.
Basically, locating the platinum in "Angel One" was like using a metal detector to find a needle in a haystack. Similarly, a metal detector would not necessarily be as useful for finding a needle in a city park unless you already had a good idea where to look.
Last edited by Ted C
on 2006-12-05 12:43pm, edited 1 time in total.
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