Research Of The Blackbody Cavity And Nonequivalence Of Spatial Cryogenic Radiometer

Optical radiation measurement accuracy is improved by at least tenfold on theground by Cryogenic Radiometer and laser, and measurement results could betraceable to the International System of Units. Because of greatly imp roved thermalproperties of OFHC copper, the sensitivity and response time constant of radiometerwere optimized greatly in a very low temperature (4K-30K). Learning fromCryogenic Radiometer on the ground, Spatial Cryogenic Radiometer is intend to bebulided, and the current spatial optical measurement accuracy will be improvedtenfold with stable sunlight as light source. A0.02%and0.1%level of uncertaintywill be achieved for solar total power and spectral power, respectively. Opticalradiation measurements which can be traceable to SI will be achieved in space.Firstly, the structure and working principle of spatial cryogenic radiometer wereelaborated. Through the establishment of a mathematical model of optical powermeasurements, nine factors were found. After a rough classification and distributionof total uncertainty, two main factors—the absorptivity and nonequivalence N wereattended which are very important but not yet explored in depth. This two mainfactors were researched theoretically and experimentally in depth in this paper.In order to get a ultra-high-precision measurement of solar total power, theradiation should be almost completely absorbed. The Monte-Carlo method was usedto calculate the absorptivity of black cavities, and the calculation results directed the research of the shape of cavities. A almost perfect cavity was designed theoretically.In order to measure the absorptivity of blackbody cavities precisely, a newmeasurement method was proposed which included a standard whiteboard, a standardblackboard and blackbody cavity. After several measurements, the measurementaccuracy can be enabled.On the research of nonequivalence, a finite element mode l was establishedaccording to experimental results in vacuum. From the ANSYS thermal analysis, wefound that multilayer cavity structures can be simplified to monolayer structure.Then, through solving SIAR’s heat conduction equations, we found that in orderto fully grasp the response characteristics of the blackbody cavity, elements’ responsecharacteristics were important. This is an effective method for the calculation ofnonequivalence which is due to different optical or electrical loading areas. Throughthe calculation of elements’ response in FE analysis, the response of the blackbodycavity can be grasped.Finally, the FE method was used to solve the TSP and HS cavities’ response.Due to the lack of experimental data, the TSP and HS cavities’ FE model were basedon the assumption. The calculation aim of Spatial Cryogenic Radiometer was not foraccurate results, but for clear calculation ideas and effective calculation methods. Theaim of this part of work is to establish a solid theoretical basis for subsequentresearch.