Above-low-cloud aerosol (ACA) has important impacts on low clouds bellow. Based on the satellite data from 2007 to 2010, this study analyzed the relationship between ACA optical depth (OD), ACA occurrences and low cloud integrated color ratio (CR) over tropic Atlantic region where ACA frequently occurs. The results show that, the integrated attenuated CR (IACR) of low cloud is about 30%-50% larger over smoke region in smoke outbreak seasons than other regions or seasons. However, the IACR of low cloud over dust region shows small difference between dust outbreak seasons and other seasons. It indicates that above-low-cloud smoke aerosol can introduce stronger color effect than dust. The integrated corrected CR (ICCR) of low cloud tends to decrease with increasing above-cloud dust OD, while the low cloud ICCR shows weak relationship with above-low-cloud smoke OD. And, the above-low-cloud dust aerosol could introduce strong microphysics effect, that is, the low cloud droplet size may decrease with increasing burden of dust aerosol above.
In this paper, a new idea is put forward under the background that static high voltage DC power is commonly used to replace lightning in the femtosecond laser-guided lightning simulation experiment. We use a single chip microcomputer as the controller to generate controllable Pulse Width Modulation(PWM) wave signal,then through PWM control high voltage.So controllable high voltage in the femtosecond laser-guided lightning simulation experiment is formed by the method of weak voltage(namely PWM) controlling high voltage. In the experiment, the period and duty ratio of PWM output by the single-chip microcomputer are indirectly controlled by controlling the internal timer counter A, optocoupler and SCR are used as the safe isolation module between high and weak voltage. The experimental results show that the controllable high voltage in the femtosecond laser-induced high voltage discharge experiment can be easily and effectively obtained by adding a controller to control. At the same time, it can help us to analyze the influence of the different high voltages on the experimental parameters of femtosecond laser guided high voltage discharge.
A ground-based Fourier transform spectrometer has been established in Hefei, China to remotely measure H2O, CO2, CH4 and CO based on near-infrared solar spectra. The continuously retrieved time series of total column results for H2O, CO2, CH4 and CO are presented on April 2nd, 2018. The observation results show the variation of total column of CO2, CH4 and CO. The total columns of H2O, CO2, CH4 and CO are 1.35×10 23, 8.91×1011, 4.08×10 19 and 4.09×10 18 molecules/cm2, respectively. In order to reduce the systematic error of the instrument, we also calculate the column-averaged dry air mole fraction by the oxygen molecule as the internal standard. The column-averaged dry air mole fraction of H2O, CO2, CH4 and CO are 5289.43, 415.04, 1.907 and 0.178ppm, respectively. Furthermore, we analyze the atmospheric transmittance by using MODTRAN 5.0 based on the retrieved results. The comparison results show that the atmospheric transmittance has gaps in the absorption band
Laser ablation absorption spectroscopy (LAAS) is an analytical technique by combining diode laser absorption spectroscopy (DLAS) with laser ablation (LA) technique. It has been developed to atomize various samples and distinguish elements and isotopes directly without chemical separation. This article reviews the principle and recent research highlights of LAAS technique.
A new method, named FSI (Fourier Shear Interferometry), is suggested to calculate the phase derivative by Fourier transform of the lateral shear fringes. After filtering intensity spectrum AF2 (fx, fy)in the spectrum of the shear fringes, the cross term of the fringe’s intensity, i.e., A(x,y)A(x + s, y)exp[i▵xφ(x,y)], is obtained by the reverse Fourier transform, and then ▵φ(x, y) can be easily obtained if only |▵φ(x, y)|less than or equal to π. The numerical simulation results demonstrate feasibility and accuracy of the suggested method.
The beam spreading, induced by atmospheric turbulence and thermal blooming when a high-energy laser beam propagates through the atmosphere, is numerically calculated and analyzed. The simple scaling relation between the beam quality factor and the characteristic parameters of atmospheric effects is obtained, and can be given by the expression β2u = 1 + 0.636N1.558. Moreover, when the distortion parameter N is less than one, the beam spreading is mostly dependent on the linear effects because of the weak thermal blooming effects. However, with the thermal blooming effects strong gradually, the beam spreading induced by the combined effects of turbulence and thermal blooming increases rapidly.
By using the time-dependent propagation computer code, adaptive compensation for thermal blooming effects, which are induced by collimated high-energy laser (HEL) beam propagation through the atmosphere, is numerically calculated and analyzed under different conditions. The numerical results show that, with the definite adaptive optics (AO) system, the scaling parameter NJY'NFB is available to evaluate the effect of adaptive compensation efficiently. Moreover, we get the scaling relation between the scaling parameter ND/NFB and the far-field Strehi ratio, which is can be described by Strehl=1/[1+AND/NFB+B (ND/NFB) C] where A, B and C are fitting parameters. We also get the threshold of adaptive phase compensation instability (PCI) through analysis ofthe scaling relation above. In addition, we discuss the difference between adaptive compensation and whole-beam compensation.