Research On Sky Background Spectral Radiance Measuring System For Self-adapting Object Track

With the development of space technology, the photodetection of spatial object becomes an important research direction for all over the world. While spatial object is detected by the subearial equipment, the radiometric information received by detection system includes the atmospheric scattering and absorption of solar radiation by gas molecule and aerosol, besides the self-emitted radiation of spatial object. Both of the scattering and absorption make up of the sky background radiance. The majority of subearial photodetection equipment distinguishes the spatial object by comparing the radiant intensity and the spectrum between object and sky background. The spectral radiance difference between spatial object and sky background directly decides the detecting quality. Thereby the precision measurement of sky background spectral radiance is the prerequisite and foundation for detecting spatial object and ground-to-air remote sense.The traditional sky background spectral radiance measuring instrument mostly adopts fixed operation mode. It only measures the given district of sky background. By reason of the whole measuring process is independent of the flightpath, thereby it is not able to achieve realtime measure for sky background spectral radiance of spatial object flightpath. On account of the shortage of measuring accuracy and punctuality, an automatic sky background spectral radiance measuring system for self-adapting spatial object track is proposed. The spatio-temporal coincidence relation between measuring equipment and spatial object is established by this system. The automatic measurement for sky background spectral radiance is realized. The system is able to satisfy the requirement of measuring accuracy and punctuality for spatial object detecting field. The primary coverage of this paper is as follows:First, the frame and component of aerosphere are introduced. The absorption and scattering of gas molecule and aerosol in the atmosphere are analyzed. This paper explains the atmospheric influence for sky background spectral radiance and introduces the transmission model of atmospheric radiation, such as MODTRAN.Second, an automatic sky background spectral radiance measuring system for self-adapting spatial object track is devised. This system has twin shaft frame. The horizontal axis and vertical axis are drived by straight flow moment dynamo. The photoelectric encoder is used for real-time measurement for pitch angle and azimuth angle. The system is able to display the real-time position information by the Global Position System (GPS), such as longitude, latitude, altitude and so on. The system includes measuring radiovisor system, which can establish reference direction by measuring fixed star. The receiver of system consists of integrating sphere and optical fiber spectrograph, which can enhance the accuracy and punctuality of data acquisition.Third, the wavelength calibration, the radiation standard transmission and the spectral radiometric calibration have been used for ascertaining the spectral response of the system. The spectral response can applied to data acquisition and data processing, which inverts digital quantity to sky background spectral radiance. The calibration result indicates that the maximum wavelength error is0.31nm, and the uncertainty of spectral radiometric calibration is2.96%.Fourth, the guiding measuring experiment fulfill in external field by using this system. The measurement of the system compares with the analog calculation which is provided by MODTRAN. The comparative result indicates that both of the two measurement curve shapes are analogical, and the sky background spectral radiance characteristic which is measured by the system is in agreement with the actual characteristic of sky background. The system is able to achieve automatic spectral radiance measuring.