Noise

Including instrument noise and environmental noise.

Instrument noise:

Fading noise

Still need some backscatter energy to make data reliable.

Show the higher amplitude level in short distance. The amplitude change to a lower level because of interference of wave.

We could use multiple laser frequencies to mitigate the noise level. sacrifice spatial resolution to significantly reduce the noise.

If the instrument is unstable, there will be laser drifting noise. Independent to the channel.

Could be easily removed using many signal processing method.

we could only measure: \(\|\delta \phi\|<\phi\);

\[\|\delta \varepsilon_{xx}\|<\frac{\lambda}{4nL_G\xi}\]

Convert to strain rate:

\[\|\dot{\varepsilon}\|=\frac{\|\delta\varepsilon_{xx\|}}{dt}=\dots\]

It is different from geophone(maybe it will be similar in intensity-based system, but different in phase-based system)

Maximum pulse rate != output sampling rate. Down-sample is OK if we do not lose information.

GL should be much larger than pulse width or there will be some non-linear components in measurement.