Dynamic distributed sensing of strain and temperature is the key for real-time structural health monitoring (SHM) across a wide range of geo-engineering challenges, for which Brillouin Optical Time Domain Analysis (BOTDA) and Rayleigh Coherent Optical Time Domain Reflectometry (COTDR) are promising candidates. A noise model with specific parametric simulation of the two systems has been developed. Noise in both laser(s) and detector is independently simulated to identify the key noise sources. In this simulation, although averaging can significantly enhance the signal-to-noise ratio (SNR) in the two systems, it is a barrier to dynamic sensing due to its time-consuming accumulation procedure. The sequence of averaging in the signal processing workflow can vary the SNR for the two systems. The system components should be optimized to reduce the averaging times to achieve the required system specifications, especially the dynamic sensing performance.