Random Noise and Its Impact on Measurement Precision Employing RZPN Code Modulation of Fiber Lasers

The Return-to- Zero (RZPN) Pseudo Noise modulation technique is a promising approach for making range resolved measurements of CO2 within the planetary boundary layer (PBL) using low cost, commercial, off-the-shelf, components. While it enables the use of high duty cycles with CW laser systems it also modifies the background count rate with unexpected consequences on signal retrieval. The on and offline signals are derived by cross correlating the return signals with the appropriate transmit kernels. Noise counts that result when actual data undergoes cross correlation have a much larger impact on measurement precision than one would expect given the signal to noise ratio. A discussion of the RZPN technique will be presented including the results of a detailed analytical study comparing retrievals using various codes ranging from 127 through 4095 bits. An assessment on how these codes treat random background counts, their resulting impact upon specie retrievals and measurement precision will be addressed.