Aiming at the detection of benzene concentration in the atmosphere, a power-modulation scheme with laser wavenumber tuning is proposed in mid-infrared integrated-path differential absorption (IPDA) lidar. Based on the differential absorption lidar (DIAL) theory, we design the configuration of power-modulation IPDA lidar. Its central measurement and reference wavenumber are selected as 3090.3cm-1 and 3137.7cm-1, and the power-modulation scheme of IPDA lidar is proposed through interband cascade laser (ICL) current-driving characteristic. The simulation model of power-modulation mid-infrared IPDA lidar is constructed, and then its theoretical analysis is carried out. Furthermore, the retrieval algorithm for benzene concentration is presented, and then the concentration precision as 1/f noise with different frequencies is analyzed with FFT retrievals of 1000. The detection performance of lidar such as signal-to-noise ratio (SNR) and relative error for path length and visibility is compared between direct current (DC) driving and altering current (AC) driving, i.e. power-modulation scheme. The results show that the uncertainty of concentration is consistent with the effect of 1/f noise, that the SNR increases with the increase of visibility or the decrease of path length and the relative error decreases with the increase of visibility or the decrease of path length, and that the SNR will increase with the increase in frequency, and the relative error will decrease under the same path length and visibility. Therefore, the power-modulation mid-infrared IPDA lidar can be more effective for probing benzene concentration.
The laser induced breakdown spectroscopy (LIBS) technology coupled with a principal component analysis and relevance vector machine (PCA-RVM) was used for rapidly detect the concentration of heavy metal Cr in soil. The PCA-RVM was obtained by optimizing the relevance vector machine (RVM) with PCA.LIBS spectrum of 14 soil samples with different concentration of elements were collected and used for the model training and prediction. 10 of those were selected as training sample sets to build the PCA-RVM model, and the others as test sample sets for model evaluation. Comparing with the prediction results of PCA-RVM model with that obtained using RVM and support vector machines (SVM) model, the analytical accuracy improved by 84.17% to RVM and 92.62% to SVM at the maximum, respectively. Indicating that the PCA-RVM model can effectively improve the detection accuracy and repeatability of LIBS analysis of elemental concentration in soil.
The phase transition of water vapour is typically accompanied by a change in the water vapour isotopes. The dynamics, transpiration, and condensation of water vapour in the atmosphere can also be revealed by measuring water vapour isotopes in the atmosphere. This information is crucial for understanding the water cycle in the atmosphere. Fourier Transform Infrared (FTIR) spectroscopy is widely used to monitor atmospheric trace gases. This study is based on near-infrared solar absorption spectra collected by portable Fourier Transform Infrared spectrometer (FTS) to observe the column concentration results of H2O and HDO. And the column isotope ratio δD is calculated by H2O and HDO results. The fitted root-mean-square errors (RMSE) of the spectral retrieval window of H2O and HDO were 0.107% and 0.175%, respectively. And the mean retrieval error for H2O and HDO was (0.59 ± 0.21) % and (0.94 ± 0.20) %, respectively. The calculated error of δD was 0.0035‰, which shows a high level of observational accuracy. The time series of δD obtained from September 2016 to December 2017 with a varied in the range of -5.69‰ to -369.19‰. And the lowest δD observed in January with a mean value of (-249.63 ± 32.35) ‰ and the highest δD observed in July with a mean value of (-38.61 ± 2.43) ‰, the time series show a clear seasonal variation. The observations demonstrate the capability of the FTIR spectrometer to observe the stable isotope and isotope ratio δD of atmospheric water vapour with accuracy and precision.
In this paper, the effects of turbulence intensity and transmit-receive matching angle residuals on detection performance of spaceborne coherent wind lidar were studied and analyzed. The antenna efficiency equation was derived and simulated in the target plane by Monte Carlo and Backpropagated local oscillator (BPLO) methods. Normalized CNR was defined as a measure. The antenna aperture corresponding to the maximum normalized CNR was considered optimal. We simulated the optimal aperture with different mismatch angles of 0 µrad, 2 µrad, 4 µrad, and 6 µrad under weak, intermediate, and strong turbulence intensities respectively. From the simulation results, it is concluded that:as the turbulence intensity and angular residual increase, the coherence length and the optimal antenna aperture decreases. Besides, under strong turbulence, the effect of mismatch angle on the normalized CNR is weakened and the appropriate range of antenna aperture is narrow. The optimal antenna aperture is about 400 mm under the condition of weak or intermediate turbulence.
Turbulence effect is one of the key factors limiting underwater optical transmission communication. Eddy light underwater transmission can provide a new way to realize ultra-wideband and high speed underwater optical information transmission. This paper studies the scintillation index of the modified Bessel Gaussian beam propagating in ocean turbulence, analyzes the influence of wave source parameters and ocean turbulence parameters on the propagation quality of the modified Bessel Gaussian beam, and studies the transmission characteristics of the modified Bessel Gaussian beam propagating in underwater turbulence by designing experiments. The influence of turbulent flow induced by water diffusion with different temperature and salinity differences on beam propagation is considered. The theoretical and experimental results show that smaller width parameters will reduce the scintillation index of the beam under the same ocean turbulence environment. In the selection of ocean turbulence parameters, the larger turbulent kinetic energy dissipation rates and the smaller temperature salinity fluctuation equilibrium parameters can also effectively improve the beam transmission performance, and the scintillation index increases with the increase of turbulence intensity. The research results of this paper have important reference value for the research of vortex light transmission and communication
