I want the numerical value of PSD of the probe pulse of the OTDR. How can I get the value of PSD? Also, what is the value of the maximum PSD of the probe pulse?
Maybe you could use the well-known proportion related with pulse length and period to normalize the spectra obtained with the OSA connected with your OTDR... Or you mean some another kind of PSD say in terms of vibration and phase OTDR?
if i understand it right, the pulse modulation will not have a strong influence on OTDR diode's spectra (but, sure, depends on modulation method), so you maybe need to refer to the OTDR diode's datasheet to know how does it really look like. The pulsed spectra will be lower than the diode's spectra in continuous mode due to the pauses between pulses. As i understood, you also have the FBG between OTDR and OSA? if it is so, you need to find the overlap of its function with the diode's spectra.