###### Abstract
Unlike previous studies in the wavelength range of 1.300-1.400 \(\upmu\)m, [PERSON] et al. (2013) measured the internal temperature under various pressures and temperature conditions in a three-zone electric furnace using the new H\({}_{2}\)O absorption wavelength regions of 2.474 and 2.482 \(\upmu\)m. Here, the temperature was derived from two H\({}_{2}\)O absorption signals in each scan range by using two lasers with wavelengths of 2.474 and 2.482 \(\upmu\)m [11]. In addition, [PERSON] et al. (2014) measured the temperature using the CO\({}_{2}\) absorption wavelength region of 4.174 to 4.184 \(\upmu\)m in the mid-infrared region, unlike the above mentioned study, in which the temperature was measured using H\({}_{2}\)O absorption wavelengths in the near-infrared region [12]. [PERSON] et al. (2017) used two lasers at H\({}_{2}\)O absorption wavelength regions of 2.482 and 1.343 \(\upmu\)m to measure the H\({}_{2}\)O concentrations and temperatures in the CH\({}_{4}\)/air flame [13]. Recently, applied temperature measurement methods based on the two-line thermometry method have been developed [14; 15]. This applied temperature measurement method typically consists of a temperature binning and tomography method for analyzing non-uniform temperature and concentration fields, and an intensity-modulation spectroscopy method for increasing the sensitivity of temperature measurement in high temperature/high pressure environments. These methods also used each absorption from two lasers to fundamentally increase the temperature measurement sensitivity. Temperature measurement by TDLAS was started with the two-line thermometry method using two absorption signals, as described above. Previous studies have measured the temperature using two absorption signals separated from each other within a single scan range of one laser. In addition, the temperature was also obtained from two absorption signals in each scan range using two lasers. Because the two absorption areas derived from the two absorption signals change sensitively according to the temperature change, it is difficult to accurately analyze the two sensitive absorption areas when the absorption signals partially or completely overlap; this results in an error in the temperature readings. For these reasons, most studies have used two absorption signals that were separated from each other. This corresponds to the \"appropriate spectral separation\" in the line selection method for measuring the temperature, summarized by [PERSON] et al. [16]. However, the two H\({}_{2}\)O absorption signals separated from each other within a single scan range of one laser are limited to the wavelength region of 1.300-1.400 \(\upmu\)m, in which the H\({}_{2}\)Oabsorption is most abundant. Temperature measurements systems using multiple lasers are complex and have increased costs. A situation in which the two H\({}_{2}\)O absorption signals overlap within a single scan range in the near-infrared region of 1.300-1.400 \(\upmu\)m can be advantageous if the temperature and concentration can be measured simultaneously. First, there are several high-sensitivity absorption lines that were not previously selected because of the overlapping of H\({}_{2}\)O absorption signals in the near-infrared region. Second, the TDLAS method scans an absorption signal with the corresponding wavelength by modulating a waveform with a constant period and amplitude. Thus, the wavelength scan range decreases as the frequency modulation (constant period) increases. However, high-frequency modulation is essential for measurement in fast flow fields, such as large-scale combustion systems [17]. Therefore, it is easy for the partially overlapped H\({}_{2}\)O absorption signals to be contained in a narrow wavelength region in the single scan range of a high-frequency modulation. However, despite these advantages, studies on the measurement of temperature and H\({}_{2}\)O concentration using two partially overlapped H\({}_{2}\)O absorption signals under general normal pressure conditions are insufficient.