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Dual Cavity Inter-Compensate Absolute Radiometer (DCICAR)

Posted on:2006-01-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:W FangFull Text:PDF
GTID:1102360155975981Subject:Optics
Abstract/Summary:PDF Full Text Request
Absolute radiometer is an instrument based on the principle of substitution of electrical power for radiation power during total solar irradiance measurements, which can be independent of other radiometric scale. The development of absolute radiometer with high accuracy is necessary for long term and uninterrupted solar irradiance monitoring and getting high accurate solar irradiance data.The further study of the solar irradiance's cycle, rule, trend, and the effect on the climate change will offer the evidence for forecast of long term change of whether and climate. Therefore, a Dual Cavity Inter-Compensate Absolute Radiometer (DCICAR) with two cavities put side by side was developed on the basis of the history and experience of the solar irradiance measurement and different kinds of absolute radiometers development in nearly two decades,The two cavities of DCICAR face the same FOV and are also in the same temperature environment, and can be used for measuring the solar irradiance alternately. The measurement results can be compared and validated with each other. So the effect on the result caused by the temperature drift of heat sink is reduced, and the precision is improved.The conical cavity of DCICAR adopts a new technology that the conical part and the cap brim for heat conduct are fabricated as one whole body. Through trials and errors time after time, appropriate thermal capacity and thermal impedance are chosen to reduce the heat conduct coefficient. At the end the time constant reaches 5~7s, hence one measurement time reaches <1.5min, which is half of the previous radiometers.The heat balance equation is established, various correct factors that can affect the accuracy of the measurement of DCICAR are determined or calculated, and then the correct factor is given out. The absorptivity of the conical black cavity is measured with a full hemisphere reflectance measurement instrument, which is developed to measure the absorptivity of mirror reflection and diffuse reflection simultaneously in a high precision. Its linearity has been validated and its uncertainty is calculated. The uncertainty is 0.012%.The various uncertainty items are calculated to compose the total measurement uncertainty and to get the expanded uncertainty. The uncertainty of DCICAR under one solar constant is 0.11%.In the end the determination of the spectrum range and the repetition of DCICAR are described in this paper. The repetition is better than 0.06% within the spectrum range of 0.2~50um.Then compared with SIAR-1 (Solar Irradiance Absolute Radiometer) demonstrated in the Ninth International Pyrheliometer Comparisons (IPC-IX) organized by Physikalisch-Meteorologisches Observatorium Davos/ World Radiation Center (PMOD/WRC) at Switzerland during the period from 25 September 2000 to 13 October 2000, DCICAR is well coincident with World Radiometric Reference (WRR). The correct factor of channel A of DCICAR relatively to WRR is 0.99972, and the channel B's is 0.99917.
Keywords/Search Tags:solar irradiance, absolute radiometer, DCICAR, time constant, uncertainty, comparison
PDF Full Text Request
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