I am performing a system identification by striking an experimental model with an instrumented impact hammer and measuring the strain response.
The timebase for the recorded signals is 5 microseconds and the hammer pulse width is typically around 200 microseconds. The data are recorded for 20 milliseconds prior to the hammer hit and for 60 milliseconds after.
Prior to the hammer hit, the strain signal is non-zero with both low and high frequency noise present. The low frequency noise is of most concern as this affects the quality of the system impulse response function that I subsequently compute.
Unfortunately when completing the tests I did not record a zero-reference prior to each hammer hit. Thus my questions are:
1) What methods are available for removing the low-frequency line noise from the entire signal given that the strain response is also of low-frequency.
2) Is is possible to use the first 20 milliseconds to construct a longer zero-reference signal that I may then subtract from the recorded data? If so, how?