The atmospheric extinction coefficient can be measured to obtain essential information, such as particle spectrum distribution and chemical composition of aerosols. It has an important application value in atmospheric environment monitoring, visibility measurement, and outdoor testing of optoelectronic equipment. Solar radiometer is a high-precision atmospheric extinction coefficient measurement device. However, due to its passive measurement, solar radiometer finds it difficult to measure the extinction coefficient in low visibility and during nighttime. Lidar uses an active light source to measure the extinction coefficient, with a long detection distance and an ability to obtain the distribution of atmospheric extinction coefficient profiles. However, based on the principle of backscatter measurement, the extinction-to-backscatter ratio needs to be assumed, and the optimization effect of optical parameters affects its inversion results. Therefore, it is necessary to study the transmission extinction coefficient measurement method based on active light sources.

The visibility transmissometer is usually the most typically employed instrument when using active light sources for extinction coefficient measurement. It can be categorized into four types, namely, single end, double end, triple end, and variable baseline. The double-ended transmissometer places the transmitting and receiving devices at both ends of the baseline. However, this requires light source with a high stability and is easily affected by window pollution. The triple-ended transmissometer uses two receiving systems to measure the same radiation source on different atmospheric attenuation paths. Two receiving systems are assumed to have the same pollution and parameters. Therefore, the stability and high-precision measurement of the long-term system cannot be guaranteed. It is often used to expand the measurement range of the instrument. The single-ended transmissometer sets the transmitting and receiving devices at the same end of the baseline, while the other end uses an optical reflector to bend back the beam, making it easy to achieve synchronous measurement. It can eliminate the correlation of light source jitter and reduce the sensitivity of the system to window pollution, but it cannot avoid the influence of backward scattering. The variable-baseline transmissometer measures the same radiation source on multiple different atmospheric attenuation paths using the same receiving device. This reduces the influence of lens pollution, environmental changes, and other factors, consequently improving the measurement accuracy of the instrument. Therefore, this paper analyzes the advantages and disadvantages of various methods to conduct research on a multiband extinction coefficient measurement using halogen lamps as radiation sources based on the variable-baseline measurement method. Quantitative analysis was conducted on the signal resolution, noise characteristics, dynamic range, random noise, response temperature sensitivity, and background radiation of the photoelectric detection circuit. Basic parameters, such as detection photocurrent, movement distance, measurement duration, and sampling rate, were established. Quantitative analysis was then conducted on the performance characteristics of three typical signal processing methods (least squares method, spectrum peak search method, and sampling integration method) in synchronous and quasi-synchronous measurements. The results confirmed the advantages of the spectrum peak search method and the sampling integration method in quasi-synchronous measurement. The spectrum peak search method can reduce the measurement errors caused by spectral differences at both ends compared with the commonly used phase-locked amplification technology. Moreover, it does not require reference signals from the transmitting unit and has strong independence and a wider application range. The results provide a theoretical basis for achieving high-precision extinction coefficient measurement through a variable-baseline method.

This paper analyzes the impact of photoelectric measurement from four aspects. In the analysis of the system detection circuit, starting from the extinction coefficient resolution and measurement range, the photocurrent demand and the range of researchable movement distance were established, and the reliability of the circuit was ensured through noise characteristic analysis. In the analysis of digital signal processing methods, the application of three typical signal processing methods (least squares method, spectrum peak search method, and sampling integration method) in transmissometers was studied. It was found that the least squares method is more suitable for synchronous measurement, while the spectrum peak search method and the sampling integration method are more suitable for quasi-synchronous measurement. Based on this, the measurement time and sampling rate of each point were established, and a preliminary evaluation of the accuracy of extinction coefficient measurement affected by random noise was completed. In the analysis of background radiation impact, the system can suppress the changes in background radiation. Furthermore, in the analysis of the influence of environmental temperature and humidity, the advantages of multi-baseline measurement in resisting environmental temperature and humidity changes were confirmed, but the temperature impact cannot be ignored yet.

This paper studies a multi-baseline and multiband atmospheric extinction coefficient measurement method. The development of the system detection circuit is completed based on the requirements of extinction coefficient resolution and measurement range. By analyzing the influence of random noise on transmittance measurement, the least squares method is shown to be more suitable for synchronous measurement, while the spectrum peak search method and the sampling integration method are both suitable for quasi-synchronous measurement. By studying the influence of environmental temperature and humidity on transmittance measurement, the advantages of multi-baseline measurement in resisting environmental interference were confirmed in practice. At the same time, the detection circuit system cannot completely avoid the influence of environmental temperature and background radiation. The research results indicate that the detection photoelectric current should not be less than 1.27×10^-7 A, the distance of each movement should not be less than 1 m, the duration of each measurement point should not be less than 40 s, and the sampling rate should not be less than 10 kHz. During the current research baseline distance of 5-20 m, the spectrum peak search method or the sampling integration method used for quasi-synchronous measurement can achieve an extinction coefficient measurement accuracy <0.8% as affected by random noise.