## 1 Introduction
In such lasers, the optical frequency changes in stepwise manner from pulse to pulse using a fixed value (\(\sim\)2-20 MHz) determined based on the laser cavity length. The first OFDR systems based on a self-sweeping fiber laser (see [19] and references therein) previously showed satisfactory characteristics. The OFDR system had spatial sampling of \(\sim\)200 \(\upmu\)m, sensitivity of about \(-\)79 dB (or \(-\)86 dB/mm), and a test line length of up to \(\sim\)9 m. The sensing tasks related to measuring a spatial distribution of physical quantities with OFDR systems are of general interest for various practical applications. However, due to insufficient sensitivity of first OFDR systems based on self-sweeping lasers, the first results were far from realization of distributed measurements in lines under test (LUTs) based on conventional passive fibers. In order to increase levels of measured signals, a LUT consisting of an array of non-resonant was used. The FBGs reflection maxima did not match the tuning range of the probe laser. However, the sensitivity of the reflectometer was sufficient enough to register the probe radiation scattered via the non-resonant FBGs and demonstrate the possibility of quasi-distribute temperature measurements. In particular, it was shown that the correlation analysis makes it possible to determine the temperature of each FBG in the array. An additional optimization of the OFDR system interferometer was important to increase the visibility of the interference spectra for measuring weak scattered signals [19]. It was shown that the optimization can improve the system sensitivity down to \(-\)110 dB/mm. As a result, the possibility of truly distributed temperature measurements with an OFDR system based on RLS with the self-sweeping laser radiation was also demonstrated. Moreover, the signal processing techniques are of great importance for the development of OFDR systems designed to measure weak signals, such as RLS. Different noise sources introduced through the laser instabilities, measurement system components, and the environment fluctuations can make it difficult to extract information about the magnitude of the scattering amplitude in LUTs. When an OFDR system is used to measure changes in temperature or strain along a sensing line, additional analysis of measured reflectograms is required. Thus, the development of approaches for OFDR signals processing is of great interest. In the present work, we investigate the influence of the input data processing procedure in an OFDR system based on a self-sweeping laser on the resulting reflectograms and noise level. An Er-doped self-sweeping laser with continuous-wave (CW) intensity dynamics [20] was used as a probe radiation source. The main feature of the probe source was the generation of relatively long (-ms) and highly coherent mode pulses. Long pulse duration enables improvement of the processing algorithms because there is a possibility of long accumulation of measured signals. It should be noted that such a possibility was not considered in previous OFDR systems based on pulse self-sweeping lasers (for example, [19]) because of the much shorter single-frequency generation time. It is found that averaging in the time domain leads to a significant decrease in the noise floor level (NFL). In particular, an increase in the number of averaging points from 1 to 430 decreases the NFL by 30 dB. For low numbers of averaging points (1-2), the level of RLS appears to be lower than the NFL; thus, long signal accumulation significantly improves the system performance. Finally, averaging in the frequency domain can be carried out via scanning the central frequency; however, this approach leads to a loss of information on the spectral composition of the RLS signal. The described analysis methods can be useful in the development of distributed sensors based on Rayleigh OFDR systems.