| 摘要 |
<p>An improved technique for acoustic sensing involves, in one embodiment, launching into a medium, at least four pulse-modulated electromagnetic-waves, each of said pulse-modulated electromagnetic waves having an associated frequency, the frequency separation between the first and second of said waves being different from the separation between the frequencies of the third and fourth of said waves. The energy scattered by the medium is detected and, in one embodiment, may be used to determine a characteristic of the environment of the medium. For example, if the medium is a buried optical fiber into which light pulses have been launched in accordance with the invention, the presence of acoustic waves within the region of the buried fiber can be detected.</p> |
