Environmental Oxygen Monitoring in Confined Spaces by a Mobile Sensor System Based on OA-ICOS and PSO-SVM Without Pressure Control

In this article, a mobile oxygen (O2) sensor system based on off-axis integrated cavity output spectroscopy (OA-ICOS) was developed for environmental oxygen monitoring in confined spaces using a 760-nm distributed feedback (DFB) laser without pressure control. In order to improve the detection sensitivity, wavelength modulation spectroscopy with second harmonic detection (WMS-
$2{f})$
strategy was employed. The relationship between gas concentration and waveform parameters, such as the amplitude and linewidth of the
$2{f}$
signal, was investigated. Additionally, the particle swarm optimization-support vector machine (PSO-SVM) algorithm was applied for O2 concentration inversion under different pressures. The performance of the method was verified under different pressures through experiments. Compared with the traditional nonlinear fitting method, the PSO-SVM algorithm has higher accuracy and approximate sensitivity. Based on Allan deviation analysis, the limit of detection (LoD) of the sensor system was ~0.019% at a 1 s averaging time, which can be further improved to 0.002% at an optimum averaging time of 180 s. Environmental O2 monitoring in different laboratories was performed, and the reliability of the sensor system was verified. The proposed detection technique can achieve accurate O2 detection in environments with varying pressures, presenting extensive prospects for application in environmental monitoring, breath analysis and industrial applications.