Research On Infrared Radiation Signature Of Missile Plume And Cloud Scene

The infrared radiation of missile during boosting phase and mid-course radiate mainly from its plume, and its background is most likely to be cloud. In order to distinguish attacking missile from cloud background effectively, it's necessary to study the infrared radiation signature of missile plume and that of cloud background. The infrared signature of cloud depends on the multiple scattering of water droplets or ice crystals within clouds. This project is supported by foundation of spaceflight supporting technology. Its intention is to study the infrared signature of missile plume and that of cloud, to establish radiation models for real time scene simulation in missile early-warning system.This dissertation is composed of two parts. Firstly, in order to distinguish missile form cloud background, algorithm for true temperature of missile plume and its emissivity were studied. Two new data processing algorithms for multiple wavelength pyrometer were put forward. One algorithm is approach method based on brightness temperature (AMBT). The other one is continuous measuring method based on brightness temperature (CMBT). Secondly, in order to distinguish cloud background, the multiple scattering of water droplets and ice crystals in clouds were calculated. Emissivities and transmissivities of clouds were also computed. In order to calculate radiation brightness of cloud at a distance, a new algorithm to speedup the calculation of radiation transfer equation, build-up factor algorithm was proposed.Finished research works including:â… . Put forward a new multi-spectral data processing method, AMBT. In order to avoid guessing the relationship between emissivity and wavelength, according to the relationship among brightness temperature, true temperature and wavelength, it's known that true temperature is equal to brightness temperature when the wavelength approaching to zero. Thus, the calculated true temperature can be derived through non-linear least squares fitting between brightness temperatures at different channels and the corresponding wavelengths. Simulation experiments were made at high temperature (1500~3000K), intermediate temperature (500~1500K) and at low temperature (160~500K) corresponding to the two atmospheric windows from 3 to 5 micron and from 8 to 12 micron. Actual measured data were used to validate the effectiveness of AMBT. Then stochastic noise was superimposed to evaluate its influence on the precision of AMBT. Simulation results prove that AMBT is more accurate used at low temperature than to be used at high temperature. This method can obtain true temperature of most engineering materials at a distance. Influence of stochastic noise on AMBT is uncertain. So we can use AMBT to estimate the preliminary value for other algorithms avoiding the blindness of estimation.â…¡. Described another new multi-spectral data processing method, CMBT. Supposing linear relation exists between emissivity and temperature at chosen wavelength during narrow waveband and in short measuring period, through processing measured data at two different time, spectral emmissivites at different wavelength can be obtained. Simulation results prove that CMBT can bear high random noise. All the calculation results are satisfied. Actual measured data was processed by CMBT and shows that CMBT is of high precision. This algorithm can be used in practical measurement and get better results.â…¢. Use superellipsoid equation to simulate nonspherical particles with arbitrary shapes and calculate their equivalent radius. Mie theory is used to calculate scattering of global particles, while T-matrix method is used to calculate scattering of nonspherical particles. Equivalent radius is very important in T-matrix method. Till now, most of the algorithms for equivalent radius of nonspherical particles are using integral on curved surface. They are inconvenient and time consuming. Using superellipsoid equation can shorten the calculating time for equal-volume-sphere radius and equal-surface-area-sphere radius. Program of the improved T-matrix method was compiled using FORTRAN language. Scattering parameters of ice crystals in cirrus was calculated. The computation results were compared with that of reference and proved that the improvement for T-matrix method is successful. Relations between scattering parameters and equivalent radius were analyzed. Modified Gamma distribution parameters'influence on the scattering signature of clouds was also researched.â…£. A new algorithm of calculation of radiation transfer equation, build-up factor algorithm was proposed. In order to calculate infrared signature of clouds at a distance, radiation transfer must be taken into account. Algorithms of calculation of radiation transfer equation, such as successive iterative method and Monte Carlo method, are time-consuming and couldn't be used online. As build-up factor algorithm, single scattering was calculated firstly. Then a build-up factor was defined to estimate the contribution of multiple scattering. The total scattering of particle system is the sum of single scattering and multiple scattering. Then the radiation brightness of cloud can be calculated. This algorithm can speedup the calculation of radiation transfer equation, calculate multiple scattering quickly. The results of this algorithm were compared with that of successive iterative method and that of LOWTRAN. Results show that to get the same calculating precision, build-up factor algorithm is much faster than successive iterative method and can be used in online simulation.