The components such as water vapor and aerosol in the atmosphere can lead to the blurring of high-resolution satellite remote sensing images, and the image quality will be seriously undermined. By means of multispectral imaging technology, an atmospheric correction instrument and the satellite main camera can obtain the atmospheric parameters in the same region at the same time, and the atmospheric correction for remote sensing images is carried out to improve the image quality. In the field of spectral imaging, CCD detectors are applied by most traditional cameras. However, with the rapid development of technology, CMOS detectors have been able to compete with CCD in terms of quantum efficiency, noise level, dynamic range and other key performance parameters, and have the tendency to gradually replace CCD detectors. To fill the gap of domestic scientific CMOS detectors in the field of space spectral imaging, we design a set of CMOS imaging electronics systems with high reliability and signal-to-noise ratio based on the scientific CMOS detector HR400 of Gpixel for the multispectral imaging requirements of a correction instrument project. Besides, a dynamic time-delay imaging method is proposed according to the characteristics of its filter wheel imaging, which solves the problem of polarization azimuth deviation caused by the variation of exposure time and provides a reference for the design of similar instruments.

The system architecture is based on field programmable gate array (FPGA) and static random access memory (SRAM) buffer. The driver design and image acquisition technology of CMOS detectors is discussed in detail. To address the problem that the variation of the exposure time of the filter wheel multispectral cameras will lead to the difference in the polarization azimuth, the influence of the imaging position on the polarization azimuth is analyzed first. Then, combined with the working principles of the rolling shutter CMOS detectors, a time-delay imaging method is proposed, which can be dynamically adjusted according to the exposure time. The driving schedules are designed to complete the simulation verification, and the position error of the imaging center in the dynamic time-delay imaging method is analyzed. In the stage of image storage, a 2×2 binning method is devised to improve the image signal-to-noise ratio. Finally, a test platform is built to test the imaging quality of the camera, and the signal-to-noise ratio and dark noise of the imaging system are also tested. An experiment is conducted to compare the polarization azimuth before and after using the dynamic time-delay imaging method.

For the filter wheel of multispectral polarization cameras, if the incoming light spot is taken as the starting point of imaging, the imaging center positions of the same channel are not consistent under different exposure time. The angle positions of the motor change with the variation of exposure time in the actual imaging. The increase in the difference in exposure time is accompanied by the enlargement of the difference in the polarization azimuth angle of the actual imaging (Fig. 2). The time sequence simulation of the dynamic time-delay imaging method shows that the different delay time before imaging can ensure the positions of the imaging exposure center are consistent under different integral time (Fig. 7). The angle position errors of the motor with dynamic delay compensation are about ±0.087°, which is mainly affected by the motor positioning error, with weak influences from other error sources (Table 1). The image quality test results show that the temporal dark noise is 71.6 (equivalent electron number) and the SNR is 588.1 when the system light intensity is 80% of saturation light intensity, meeting the requirements of the camera (Table 2). In addition, with the addition of delay compensation, the maximum deviation of polarization azimuth angle measured under different exposure time is less than 0.22°, which is greatly improved compared with the method without delay compensation. The time-delay imaging method can significantly reduce the polarization azimuth difference caused by exposure time (Table 3).

In this paper, an imaging electronics system based on the scientific CMOS detector HR400 of Gpixel is established according to the functional requirements of multispectral cameras and the characteristics of aerospace applications. The system structure is introduced in detail, and the driver design and image acquisition technology of CMOS detectors are discussed in particular. To address the problem of polarization azimuth difference caused by the variation of exposure time of the filter wheel of multispectral cameras, we analyze the influence of imaging position on polarization azimuth. The greater difference in exposure time is coupled with the greater difference in the polarization azimuth angle of actual imaging. Then, a time-delay imaging method is proposed, which can be dynamically adjusted according to the exposure time. The angle position errors of the motor with dynamic delay compensation are about ±0.087°, mainly affected by the motor positioning error, and the influences from other error sources are less strong. Experimental results show that the time-domain dark noise of the imaging system is 71.6 (equivalent electron number), and the signal-to-noise ratio is 588.1 when the system light intensity is 80%, which meets the requirements of camera imaging. The maximum deviation of polarization azimuth angle measured at different exposure time is less than 0.22°. Therefore, the system is expected to provide some valuable references for the in-orbit application of domestic CMOS imaging sensors and the design of similar satellite-borne remote sensing instruments.