http://www.youtube.com/watch?v=dZQT6lV-rsg", it's even more massively complicated than I thought it was. As usual, Hollywood takes something that might be interesting and blows it so far out of proportion that it's barely even fun to watch.
Even aside from the massive problems of hacking into every single phone in the entire city on a whim, I don't believe cell phones could be used as sonar. I don't think that they have the ability to generate an audio tone with a high enough frequency to be inaudible.
Plus, the phones don't have sonar processing software on them, unless Morgan Freeman remotely jail-broke every single one of them and installed the program (I'm pretty sure there's not an app for that.:p). If that's not possible, the phones would have to transmit the raw audio data.
Every phone in the area continuously transmitting just digital data of positions and sizes of objects would be a huge burden on the network. Continuous audio would require even more massive bandwidth, and certainly break the network. I'm not even talking about the massive back-end computation that would be required to interpret that audio data into a sonar image.
Even with a massive network of remote sensors, I don't think you'd ever be able to get an image of that resolution, and certainly not in anything resembling real time.
You would have to know the exact location and altitude of every sensor in relation to every other sensor, and use the data from each overlapping field to stitch together a coherent 3D model of a fairly large amount of terrain.
Seems a bit ambitious for someone with the equivalent of an Associates degree.
