Polarization that reflects the directional characteristics of electromagnetic wave, provides unique information of electromagnetic wave other than intensity. In the interactions between electromagnetic wave and atmospheric particles, polarimetry is able to effectively improve the abundance and accuracy of satellite remote sensing observation, thanks to its high sensitivities to the physical properties of particles. And polarization can significantly enhance the detection capability of the complicated atmospheric components, such as cloud and aerosol. For the first time, four types of polarimetric satellite sensor were introduced for earth observation, including directional polarimetric camera, push-broom polarimetric imager, whisk-broom polarimetric imager and multi-channel polarimetric radiometer. The related and representative Chinese polarimetric sensors are listed, with their characteristic parameters introduced and detection abilities analyzed. Then, typical calibration methods of polarimetric satellite sensors are introduced, including pre-launch laboratory calibration, onboard calibration and in-orbit calibration. Given the advantages of extra observing dimension and accuracy, high sensitivity to particulate size and shape, and enhancement on retrieving weak atmospheric signal, polarimetric satellite sensors have the abilities to obtain comprehensive and accurate aerosol and cloud parameters over the earth. These spaceborne polarimetric sensors have broad application opportunities and enormous potentials in the fields of atmospheric remote sensing, including monitoring atmospheric fine particulate matters PM2.5, observation and retrieval of essential climate variables, monitoring and assessment of extreme environmental events, evaluation of aerosol ecological effects and high-precision atmospheric correction for earth observation.

The Chinese GF-5 satellite was launched successfully in May 2018, which was equipped with a directional polarization camera (DPC). The DPC sensor’s radiometric characterization may be affected by many factors, such as the vibration during launch, the outgassing when instrument leaves atmosphere, the ageing of the optics and circuit system, resulting in a certain deviation between the in-flight performance and the preflight radiometric calibration. Based on the in-flight calibration method for polarization measurements of DPC, using the sunlight reflected within the sun’s glitter over ocean, the DPC measurements were adopted during its commissioning phase. The preliminary result shows that the measured degree of linear polarization values are consistent with the theoretically values, with small average deviations of －0.03, －0.04, －0.01 for 490, 670, 865 nm bands, respectively. It indicates that the DPC’s polarimetric characterization have not been changed significantly after launch. This method is based on natural target, and it can be used to monitor the temporal polarimetric sensitivity of DPC.

Radiometric calibration of the directional polarization camera (DPC) with high-precision is very important for quantitative scientific application of acquiring an accurate description of aerosol distributions and microphysical properties. Using Fourier series analysis method, a polarization rate measurement model is established to eliminate the measurement error introduced by the absolute direction in the angle of linear polarization of the reference light source, so that the polarization property is measured with high accuracy. Combining radiometric and polarimetric calibration model of DPC, radiometric calibration uncertainty caused by polarization property decreased from 8.8% to 2.2% after correction. Using an integrating sphere light source with large aperture and high-precision two-dimensional turntable platform, adopting sectional viewing field measurement method, the entire pixels response non-uniformity is measured and corrected, and the precision of relative radiometric calibration coefficient is better than 0.5%. To transfer the spectral radiance value, the standard lamp and diffuse reflection reference board system is introduced. According to analysis and evaluation of various factors, radiometric calibration accuracy of the entire waveband is better than 5%.

System-level polarized calibration is an important link in the development of directional polarization camera(DPC), which is of great significance for improving quantitative detection applications such as atmospheric aerosols and cloud phases. The polarization response calibration model is established combining with matrix optics and radiation theories, and key impact parameters are calibrated. An integrating sphere reference light source with large aperture and sectional viewing field measurement is used to eliminate the influence of the optical wedge plate on the non-consistency of the field view of DPC three partial channel, and high precision measurements of the high and low frequency relative transmittances are achieved. By using the Fourier series analysis method, the measurement model of the polarization degree of full view is established, and the measurement error introduced by the polarization azimuth absolute position of the reference light source is eliminated, which guarantees the precise measurement of polarization degree. The variable polarization light source and integrating sphere radiation source with large aperture are used for the comparison and precision analysis, the DPC full view polarization calibration uncertainty is better than 0.5%, and the DPC measured polarization degree uncertainty under natural light is better than 0.05%, which confirms the precision and reasonability of polarization remote sensor with wide field of view polarization radiation response calibration model. This system-level polarized calibration method can meet the requirements of high-precision polarization observation scientific application of wide field optical polarization remote sensor.

On-orbit radiometric calibration of spaceborne differential optical absorption spectrometer can be conducted based on the bi-directional scattering distribution function (BSDF) and the sun. The EMI BSDF is the ratio of EMI radiance and irradiance calibration function. Radiometric calibration of observation path is completed on the ground. Radiometric calibration of calibration path can be realized by the sun. Then EMI BSDF is obtained, and the on-orbit radiometric calibration is conducted. The results between the EMI and TROPOMI show that the accuracy of the radiance calibration is 5%～6.5%.

The relative spectral respone is one of the basic parameters for detection and evaluation of the performance of the directional polarization camera. A set of devices to measure relative spectral response of the directional polarization camera was assembled, which consisted of laser pumping xenon light source monochromator, depolarizer, reference detector and 45° beam splitter. The synchronization measurement method of beam splitter was utilized to reduce the instability of the light source. On the basis of monochromator and data acquisition system developed by different development platforms, an automatic testing system for the relative spectral response was developed by using ActiveX and dynamic link library technology to solve problems of complex testing process and long testing time. This automatic testing system has reduced the impact of time stability, and improved accuracy and efficiency of the measurement. Taking 490 nm and 865 nm channel of the directional polarimetic camera as an example of application, the experiment of relative spectral response in instrumental level measurements was carried out. The experimental results showed that the accuracy of the ratio between measured range value of the center wavelength and the average value of the bandwidth of directional polarimetic camera is within 0.11%, which meets the responsivity non-uniformity calibration requirement of less than 0.6%.

Environmental trace gases monitoring instrument (EMI) was launched on May 9th, 2018, which can effectively acquire global ultraviolet-visible signal of atmosphere scattering. EMI raw digital number(DN) is called level 0 data. For quantitative application of EMI sensing data, spectral calibration, geometric positioning and radiometric calibration are required. Then the level 1 data is obtained. The level 1 data is used as input for scientific atmospheric retrieval algorithms. Retrieval results are applied to quantitatively monitor the global air quality changes and the transmission of pollutant gases distribution, which could get spatial and temporal distribution and variation of key global atmospheric composition and pollutants (such as NO2, SO2, O3, etc.).

The absolute radiation calibration and long-term stability monitoring of the optical remote sensor can be realized by the ratioing radiation on-board calibrator, in which the diffuser illuminated by the sun is used as the reference light source, and the on-orbit degradation of the solar diffuser is corrected by the ratioing radiometer(RRM). The radiation response characteristics of the RRM is one of the main factors affecting the accuracy of the on-orbit calibration. The radiation response characteristics of the RRM is evaluated. The absolute responsivity is obtained, and the response nonlinearity and response instability are measured. The results show that the uncertainty of absolute response calibration is better than 2.88%, the nonlinearity is better than 0.93%, and the instability is better than 0.52%, which satisfies the requirements of on-orbit calibration applications.