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The Spaceborne Directional Polarimetric Camera (SDPC) is dedicated to obtain an accurate information of clouds and microphysical properties of aerosol particles via multi-angle, multi-spectral and multi-polarization observations. It images the Earth with 110° field of view (FOV) in 3 polarimetric spectral bands and 5 non-polarimetric spectral bands from visible to near infrared. Due to its wide FOV telecentric optical system and multi-channels, polarization sensitivity of optical components (PSOC) and non-uniform response of pixels (NURP) are the main uncertainty factors of polarimetric calibration.In this paper, a polarimetric calibration model of SDPC has been constructed for increasing the measurement accuracy. Combined an integrating sphere with a polarization generator as source, PSOC can be measured in high accuracy by using the Fourier series analysis method which reduces the impact form the alignment error of the generator. The sectional viewing field measurement method is used to acquire NURP while the large aperture integrating sphere served as reference source. Subsequently, the data of NURP have been corrected by the relative transmittance of high frequency and low frequency respectively for polarized channels. The result of validation experiment shows that the polarization measurement errors in 0°, 15°, 30°, and 45° half field of view (HFOV) are all less than 0.5% when the degree of linear polarization of reference source is larger than 0.1.

We propose a space benchmark sensor with onboard SI (Syst&egrave, me International) traceability by means of quantum optical radiometry. Correlated photon pairs generated by spontaneous parametric down-conversion (SPDC) in nonlinear crystals are used to calibrate the absolute responsivity of a solar observing radiometer. The calibration is systematic, insensitive to degradation and independent of external radiometric standards. Solar spectral irradiance at 380&ndash, 2500 nm is traceable to the photon rate and Planck&rsquo, s constant with an expected uncertainty of about 0.35%. The principle of SPDC calibration and a prototype design of the solar radiometer are introduced. The uncertainty budget is analyzed in consideration of errors arising from calibration and observation modes.

In order to satisfy the requirements of pre-launch laboratory calibration with high accuracy for polarization remote sensor, an innovative high precision polarimetric calibration instrument with adjustable degree of linear polarization (DoLP) in a wide dynamic range called adjustable polarization light source (APOLS) has been developed. APOLS consists of a collimated light source (CLS) and a polarization state adjuster (PSA). The PSA contains four parallel K9 glass plates, which can be orientated from 0° to 65° accurately controlled by electromechanical driving mechanism whose rotation accuracy is better than ±5″. Regarding the DoLP of APOLS, its adjustment range is from 0 to 0.72 within the spectral range from 460 to 2000 nm. The theoretical model of APOLS was established to describe the DoLP produced by multiple refraction of transmitted light. Meanwhile, the major systematic factors contributing to the DoLP uncertainty such as refractive index and absorption of K9 glass, incident angle, instability and parallelism of light source were analyzed. By using the spectro-polarimetric analyzer (SPOLA), the uncertainty evaluation experiments of APOLS were carried out. The results showed that when the DoLP value was in the range of 0.26 to 0.72, the uncertainty was less than 0.5%, and when the DoLP value was in the range of 0.003 to 0.26, the uncertainty was in the range of 8.5993% to 0.5534%. Moreover, the uncertainty was in the range of 0.0027% to 0.0032% when the uncertainty of the CLS was not considered. The consistency evaluation between APOLS and SPOLA ranged from -0.36 to 0.6 indicates the experimental results are satisfying. It can be concluded that the APOLS significantly improved the dynamic range and accuracy of the polarimetric calibration instrument.

Out-of-band response (out-of-band light leaks) is a significant uncertainty factor in multi-spectral remote sensing instruments radiometric calibration. In this paper, a method using a spectrum-tunable reference light source (STIS) which possess new functions of continuous and discrete spectral coverage to measure, correct and validate the 443 nm band of a multi-spectral camera has been mentioned. Adjusting STIS output two discrete radiance spectrum with its spectral width of about 50 nm in the out-of-band spectral region to directly measure out-of-band radiance responsivity. Correcting out-of-band response via spectral radiance measured by reference spectral radiometer and out-of-band radiance responsivity with the help of out-of-band response correction model. Validating out-of-band response correction accuracy via contrasting the relative departure between band-weighted radiance measurement of 443 nm band with out-of-band response correction and reference spectral radiometer measurement, under the conditions of measuring the test continuous spectrum produced by STIS. The result shows that the relative departure between the band-weighted radiance and the reference is decreased from 8.8 to 3.1% before and after the out-of-band response correction. The results demonstrate that STIS is suitable for measuring, correcting and validating the out-of-band response of multi-spectral remote instruments.

Polarization observation of sky radiation is the frontier approach to improve the remote sensing of atmospheric components, e.g., aerosol and clouds. The polarization calibration of the ground-based Sun-sky radiometer is the basis for obtaining accurate degree of linear polarization (DOLP) measurement. In this paper, a DOLP calibration method based on a laboratory polarized light source (POLBOX) is introduced in detail. Combined with the CE318-DP Sun-sky polarized radiometer, a calibration scheme for DOLP measurement is established for the spectral range of 440–1640 nm. Based on the calibration results of the Sun-sky radiometer observation network, the polarization calibration coefficient and the DOLP calibration residual are a nalyzed statistically. The results show that the DOLP residual of the calibration scheme is about 0.0012, and thus it can be estimated that the final DOLP calibration accuracy of this method is about 0.005. Finally, it is verified that the accuracy of the calibration results is in accordance with the expected results by comparing the simulated DOLP with the vector radiative transfer calculations.

We have developed a method to design and calibrate the high-precision variable polarization light source (VPOLS) with an accuracy better than 0.0013. According to the design model, a novel technique for the calibration of the VPOLS based on the autocollimator and the optical auxiliary apparatus was presented and discussed; moreover, the degree of linear polarization (DOLP) comparison tests of the VPOLS compared with Spectro-polarimetric Analyzer (SPOLA) have been carried out. Experimental results show good consistency between the numerical calculated DOLP values of the VPOLS and the measured values of the SPOLA.