Research On The Traceability And The On-orbit Emissivity Measurement Method Of Space Primary Standard Blackbody

Infrared remote sounders are moving toward having high-spectral resolution and high quantification.In particular,in the fields of climate change observation and numerical weather prediction,the timely detection of decadal climate signals above natural variability requires measurements with a high level of accuracy.For example,the climate change observation requires the thermal infrared radiance with combined uncertainties better than 0.1 K(k=3)in radiance temperature,and the stability better than 0.04 K in every ten years.It poses unprecedented challenges to the design of infrared remote sounders,which requires not only the highly stable infrared detectors,but also high-accuracy on-orbit radiation calibration sources.This high level of uncertainty,proven on orbit,has not yet been accomplished by space-based high resolution infrared sounders.At the same time,the determination of satellite sensors uncertainty during prelaunch calibration cannot be assumed to be valid over the operational lifetime of the instrument.Demonstration of adequate instrument uncertainty levels during the mission requires that diagnostics be performed on-orbit,confirming that the uncertainty budgets obtained during prelaunch calibration are still tenable.An on orbit primary standard blackbody radiation source was developed to meet the application requirements by achieving the temperature stability of better than 0.01 K and the uncertainty of better than 0.15 K.Seven kinds of miniature phase change fixed points(MFPs)are designed and embedded into the rear of blackbody cavity.The MFPs defined by the International Temperature Scale of 1990(ITS-90)are used to calibrate the temperature,so that the blackbody temperature is traced to the ITS-90.A long-term experimental results are shown that the Ga MFPs is better than 3 mK(k=1)during more than 3 years.The uncertainty of seven kinds of MFPs,including Water,Gallium,Gallium-Indium,Gallium-Tin,Gallium-Zinc,Phenyl salicylate and butanedinitrile,is better than 10 mK(k=2).Two kinds of emissivity measurement method working on orbit are proposed to achieve emissivity measurement of the on-orbit blackbody source.The emissivity measurement methods are based on the controlling surrounding radiation and based on the normal-hemispherical reflection characteristic of blackbody,respectively.In a word,the on-orbit primary standard blackbody has been set up based on the MFPs as the temperature standard and the emissivity of blackbody cavity measurement.The emissivity measurement method based on controlling the surrounding radiation is implement to install a heated halo in front of the blackbody,so that the background radiation arrived at the blackbody is mostly from the heat halo.The blackbody radiation is then measured with the heated halo at two different temperatures.The blackbody emissivity is obtained based on the amount of radiation reflected from the heated halo in two different temperature.This method is used to measure the emissivity of four kinds of the high emissivity coatings,including Pyromark,811-21,JSC-3 and carbon nanotube.The results are 0.901,0.964 and 0.979,0.997,respectively.The surface microstructures of four coatings,obtained by scanning electron microscopy,are strong correlation with the value of the emissivity.The emissivity of the on-orbit primary standard blackbody radiation source are measured with spectral band(8 ?m~14 ?m)and spectral resolution form.The results are consistent with each other,the difference of the results is less than 0.06% at the same wavelength.The uncertainty is 0.29%(k=2).An improved emissivity measurement method based on the normal hemispherical reflection characteristic is proposed.A quantum cascade laser as a light source is used to illuminate the blackbody cavity.The laser power reflected by the blackbody cavity in hemisphere is estimated by measuring the reflected laser power in normal direction and the relationship between the normal and the hemispherical reflection of the blackbody.The blackbody emissivity is the ratio of the laser power reflected by the blackbody to the laser output power.The emissivity of on orbit primary standard blackbody radiation source are measured,the difference between the blackbody emissivity results measured by this method and the other two methods is less than 0.06% at the same spectrum,and the standard uncertainty of the method is 0.38%(k=2).The accuracy of the radiation from the on orbit primary standard blackbody radiation source was verified by studying the comparison method between the on orbit primary standard blackbody radiation source and the standard blackbody in the vacuum low background infrared hyperspectral radiance temperature measurement standard facility(VRTSF).The high-resolution,high-spectral radiation values of the standard blackbodies are used to compare with the on orbit primary standard blackbody radiation source by Fourier transform infrared spectrometer.The standard uncertainty of the VRTSF in 10 ?m is 0.036 K@190 K,0.026 K@300 K,0.030 K@400 K.Laboratory calibration verified the validity of the radiation value of the space primary standard blackbody radiation source in the temperature range of 273 K to 313 K.The difference between the theoretical calculation radiation values and the actual measurement results at different wavelength are less than 10 mK at each temperature points.The results show that the temperature stability of the blackbody is better than 10 mK.The temperature uniformity of the blackbody bottom is better than 10 mK at different temperatures,and the axial temperature uniformity is better than 38 mK.The uncertainty of the blackbody is 84 mK(k=2).The validity of the values of the space blackbody radiation source during on orbit operation time is guaranteed through the research of the blackbody on-orbit temperature calibration and emissivity measurement techniques.This is of great significance to improve the quantification level of infrared remote sensing instrument.