Atmospheric transmittance can critically affect the accuracy of measuring infrared characteristics exhibited by targets. On the whole, the existing measurement of atmospheric transmittance has complied with the engineering calculation results of the MODTRAN software by applying several vital parameters (e.g., temperatures, air pressures and water-vapor content). In general, the error of such a method exceeds 20%, and it is significantly impacted by local weather. In this study, a ratio correction method was adopted to decrease the error in measuring atmospheric transmittance. The correction factor was determined by comparing the directly measured value from the infrared images of reference blackbody at different temperatures with the calculated value of the MODTRAN. Subsequently, the correction factor could be exploited to correct atmospheric transmittance. The experiment for measuring infrared radiation was performed, and the radiance inversion error was reduced by more than 10% after the correction of atmospheric transmittance. Furthermore, the correction factor calculated from LWIR images could be extrapolated to other bands. Besides, the inversion accuracy of the infrared radiation characteristics significantly increased. Thus, the multi-band applicability of the correction method was verified.
Thermal blooming can have a major impact on high energy laser (HEL) beam propagation in the atmosphere. Previous analyses about this effect are mainly focus on monolithic beam. In this paper, the numerical framework of atmospheric propagation of coherently combined beams is established. The corresponding time-dependent wave optics simulation code is also developed and utilized to investigate the propagation properties of coherently combined beams under various thermal blooming conditions. For the purpose of comparison, the simulations of atmospheric propagations of incoherently combined and monolithic beam are also included. In the end, the effect of fill factor is investigated in a preliminary manner. The beam propagation efficiency (BPE) as the performance metric of coherently combined beam is employed in this paper. The results show that the thermal blooming places a significant limit on the ability of coherently combined beams. The BPE is degraded significantly under the strong thermal blooming condition. Consequently, coherent beam combining is ineffective under typical atmospheric conditions.
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