Special issue-Research of optical transmission in the atmosphere and its applications
Atmospheric parameter model and its application in the calculation of atmospheric raditaive transfer
2019, 48(12): 1203001. doi: 10.3788/IRLA201948.1203001
[Abstract](545) [PDF 1103KB](63) [Cited by] ()
The calculation accuracy of atmospheric radiative transfer depends greatly on the precision of atmospheric parameters. The establishment of a local atmospheric parameter model plays an important role in the calculation of atmospheric radiative transfer for the photoelectric engineering. By using the data of currently available, including balloon-sounding data, satellite observation data, and some surface observation data at different areas in China, a preliminary model of atmospheric parameters was established, including the daily average, monthly average and yearly average profiles from the ground to 120 km of atmospheric temperature, humidity, air pressure, and density, as well as the monthly average of the ground visibility, covering the 91 observing stations in China. These parameters were integrated in the Combined Atmospheric Radiative Transfer calculation software (CART) to calculate atmospheric transmittance and atmospheric background radiation. The spatial distribution of atmospheric parameters of 5 stations and the monthly distribution of atmospheric thermal background radiation and its geographical distribution in China were shown in the paper.
2019, 48(12): 1203002. doi: 10.3788/IRLA201948.1203002
[Abstract](731) [PDF 1635KB](48) [Cited by] ()
The actual effect of laser propagation in the atmosphere is not only related to its own propagation mechanism, but also closely related to atmospheric factors. Therefore, to accurately evaluate the effect of laser atmospheric propagation, it is not only necessary to carry out the mechanism research and establish the mathematical model of laser atmosoheric propagation, but also mecessary to carry out measurement, analysis and prediction of the optical characteristics of the atmosphere in the propagating process. Considering the complexity of the real atmospheric environment and the interaction of many factors, most of the researches adopt the physical experiment or the numerical simulation with controlled parameters to quantitatively reveal the influence of various atmospheric factors on laser propagation. Based on a large number of field measurements and the physical correlation analysis, the research of atmospheric optical characteristics focuses on the parametric modeling of optical turbulence. The development of the performance evaluation technology for the high energy laser was briefly introduced when propagating in the atmosphere at home and aboard, and its development trend for the practical application of high energy laser system in the future was pointed out.
2019, 48(12): 1203003. doi: 10.3788/IRLA201948.1203003
[Abstract](608) [PDF 1272KB](38) [Cited by] ()
Quantitative identification of cloud is very important in meteorological satellite data retrieval, and the result of cloud detection affects the accuracy directly. In fact, the cloud detecting technology is actually a process of distinguishing the objects and background, and the purpose of detection is to extract cloud features. Therefore, much signals processing and system algorithms have been applied to the technology of cloud detection. The matching pursuit algorithm (MP) is a very effective algorithm for feature extraction, which is developed in recent years, and the Orthogonal Matching Pursuit algorithm (OMP) can improve the signal-to-noise ratio more effectively. In this paper, Orthogonal Matching Pursuit algorithm and multi-channel threshold method were combined to carry out relevant research on cloud detection of MODIS data. Based on the MODIS cloud detection results, it could be proved that the integrative algorithm of multi-channel threshold combined with the Orthogonal Matching Pursuit algorithm would be more effective to cloud detection.
2019, 48(12): 1203004. doi: 10.3788/IRLA201948.1203004
[Abstract](563) [PDF 1703KB](44) [Cited by] ()
The total atmospheric transmittance is an important parameter reflecting the optical properties of the atmosphere. In the fields of atmospheric radiation, remote sensing, air quality monitoring and opto-electronic engineering, it is necessary to make a deep study on the atmospheric transmittance. In this paper, the methods of acquiring atmospheric transmittance were discussed in detail, and the latest progress and related problems of different acquisition methods were analyzed. The characteristics of software based simulation and direct measurement were compared and analyzed, and at the last, the future research was also prospected.
2019, 48(12): 1203005. doi: 10.3788/IRLA201948.1203005
[Abstract](381) [PDF 1488KB](23) [Cited by] ()
The scattering phase function is an important parameter for studying the optical transmission characteristics in aerosols. Four approximate scattering phase functions commonly used in Monte Carlo simulations in atmospheric radiation propagation were compared. Aiming at the problem that the parameters of the Two-Term Henyey-Greenstein (TTHG) phase function were difficult to determine, a TTHG scattering phase function based on particle swarm optimization was proposed. This function can well fit the Mie scattering phase function, especially at backscatter angles greater than 90. Compared with the phase functions such as HG, HG* and RHG, the phase function proposed in this paper can better approximate the actual scattering and obtain more accurate Monte Carlo simulation results.
Measurement and error analysis of the atmospheric transmissivity in M' band based on radiative transfer
2019, 48(12): 1203006. doi: 10.3788/IRLA201948.1203006
[Abstract](485) [PDF 1379KB](17) [Cited by] ()
The atmospheric infrared radiance was measured at Ali, Delingha and Huairou observing station using a self-made measurement system in the infrared M'(4.605-4.755 m) band. Based on the blackbody calibration and the radiative transfer equation, a simplified relation between the effective output value, the average zenith atmospheric transmissivity and the zenith angles can be obtained. Atmospheric infrared radiation of different zenith angles at three Astronomical Station were measured and scanned, and the above formula was used to fit the average atmospheric transmissivity of the M'band. The measurement results show that the weighted average values of the atmospheric transmissivity in the three places are 0.805, 0.758 and 0.650 respectively, with the fluctuations of 0.081, 0.250, and 0.073 respectively. The average transmissivity simulated by MODTRAN software was respectively 0.851, 0.805, 0.615, which was close to the results from the measurement. The error analysis shows that the propagation error decreases with the increasing effective output value. The theoretical error of indirect measurement method was analyzed to be less than 10%. This paper provided a on-site and real-time measuring method of the atmospheric infrared transmissivity independent of meteorological data.
Research on simulation of earth background radiation in infrared early warning satellite detection waveband
2019, 48(12): 1203007. doi: 10.3788/IRLA201948.1203007
[Abstract](552) [PDF 1646KB](30) [Cited by] ()
Aiming at the problem that remote sensing data of detection band of infrared early warning satellite(IEWS) is difficult to obtain, the earth background radiation simulation method of IEWS detection waveband based on retrieving earth surface temperature was studied. The earth surface temperature distribution maps were generated by using a generalized single-channel algorithm for retrieving earth surface temperature of the FY-3/MERSI datasets. On this basis, the earth infrared radiation model was constructed, which fully considered the influence of altitude, atmospheric model, surface type and other factors on earth surface radiation. The joint programming of MATLAB and MODTRAN was used to calculate the surface radiation corresponding to each pixel, and realize the generation of earth background radiation image of IEWS detection band. The simulation results show that the simulated images have high resolution, and can accurately reflect the earth background radiation characteristics of IEWS detection waveband. The research result provides scene data support for studying IEWS operational effectiveness evaluation and target recognition technology.
2019, 48(12): 1203008. doi: 10.3788/IRLA201948.1203008
[Abstract](571) [PDF 1568KB](36) [Cited by] ()
In order to implement measurement of the close wind field accurate and real-time, a laser anemometer based on CW coherence detection was designed with eye-safe band 1.55 m. The system optical path employed the all-fiber structure to enhance the operational stability. The telescope adopted a coaxial transmission structure with effective aperture of 70 mm and focusing distance of 80 m. The backscattered signals were processed by using the on-board programmable gate array chip on the A/D capture card and spectral centroid algorithm was also designed for wind velocity estimation. The anemometer realized high real-time and reliability. The long-term radial wind speed measurement results proved that the laser anemometer output signal was stable with a time resolution of 1 s and the lower limit of the wind measurement range was about 0.915 m/s. Compared with a calibrated pulsed coherent wind lidar, the correlation coefficient of wind speed data measured by the two devices was 0.997, the standard deviation was 0.090 m/s, and the maximum difference was 0.480 m/s.
2019, 48(12): 1203009. doi: 10.3788/IRLA201948.1203009
[Abstract](515) [PDF 1908KB](23) [Cited by] ()
In order to better detect the vertical profile of the tropospheric atmospheric water vapor, some improvements have been made to the established 935 nm differential absorption lidar. Taking the dual-channel receiving measure, the near-field channel telescope is also a beam expander that emitted laser light. The polarizing beamsplitter and quarter wave plate were used to isolate emitted light and echoed light in near-field channel, cassegrain telescope was applied in the far-field channel(main channel), thereby the near-ground dead zone of the lidar was reduced. The wavelength was shifted to 936.0-936.5 nm. The power of seed laser and the purity of the emission spectrum was increased, thereby the detection accuracy was improved. The detection span range was extended from 600-2 000 m to 250-3 000 m, and the random error was 5%.
Measurement and analysis of atmospheric infrared background radiation of typical astronomical observatories
2019, 48(12): 1203010. doi: 10.3788/IRLA201948.1203010
[Abstract](915) [PDF 504KB](37) [Cited by] ()
The intensity of background radiation directly determines the sensitivity limit of the infrared telescope system and directly affects the system design. Background radiation is also an important index to reflect the astronomical observing conditions and performance of observatory stations. The atmospheric infrared background radiation of Ali, Delingha Observatory and Huairou Observatory astronomical observatories were measured, particularly the first-hand data of atmospheric infrared background radiation were obtained for the Ali astronomical observatories. The measured results show that the atmospheric infrared background radiation intensity and the diurnal variation of the radiance on the Ali astronomical observatories are the smallest among the three stations, and the average values of the highest radiance is 1.3010-6 Wcm-2sr-1. The maximum diurnal variation of Ali's radiance mean value is only 18%. Therefore, the lowest infrared background radiation limits is Ali astronomical observatories. The second is Delingha Observatory. Finally, the measured radiance in sky sweeping was compared with the MODTRAN software simulated radiance. It is found that there is quite a difference between the simulation results and the actual measurement in the high altitude areas of the Qinghai-Tibet Plateau, whether it is the standard atmospheric mode or the actual atmospheric mode.