Citation: | Ning Yonghui, Shi Junxia, Liu Chunxiang. Design and data processing of TDICCD real-time radiation correction system[J]. Opto-Electronic Engineering, 2019, 46(12): 190112. doi: 10.12086/oee.2019.190112 |
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Overview: As to the radiation calibration process of the TDICCD mosaic imaging system in space, it rotates the focus panel of the camera 90 degrees, and then takes photos to the ground radiation calibration field, getting the real-time calibration images of the TDICCD mosaic system. It corrects the TDICCD PRNU with 1-spot algorithm based on the real-time calibration images, and calculates the differences among the pixels and the channels. It verifies the performance of the real-time pixel correction algorithm in space, and enhances the specifications of the TDI-CCD mosaic system.
When rotating the camera focus panel, for all the pixels of TDICCD pointing to the same spot-scene group in the ground calibration field, it makes sure that the real-time radiation calibration could get better results if the ground calibration filed is of the same attribute in reflectivity. We analyse the control method of the imaging period, give the final calculation method by the use of the calibration imaging data, and finally describe the relationship between the calibration field range and the valid calibration imaging data positions. These descriptions give a detail design method of the real-time calibration correction system in space.
The proposed method can distinguish the strange pixels and the normal pixels in TDICCD mosaic system, which gives processing methods separately when using 1-spot algorithm to implement the TDICCD real-time calibration correction system. Considering the efficiency of the TDICCD pixel correction parameters got in ground calibration, a tactic is designed to enhance the reliability of the real-time pixel correction parameters; meanwhile, we design the diagram of the real-time calibration algorithm and the control flow in Xilinx FPGA, which gives a detail description of the pixel correction parameters storage and applications methods.
FPGA is used to calculate and save the parameters, and an optimization design is implemented to improve the system stability and reliability. We enforce the simulation experiments in lab with respect to the real-time radiation calibration algorithm, and give a comparison among different imaging calibration cases, such as ground calibration experiments, real-time calibration simulation experiments, and no calibration experiments. The results show that the real-time radiation correction algorithm could improve the performances of the PRNU in TDICCD mosaic system, and the PRNU of the TDICCD mosaic camera system in-channel reaches 2.01% after real-time calibration. This method is useful in real-time radiation calibration, and could get a better result in project.
Diagram of camera real-time radiation calibration by rotating camera 90 degrees. (a) Normal imaging mode; (b) Real-time radiation calibration
The valid moment of the real-time radiation calibration image data below 64 integrated grades
The structure diagram of real-time calculation to the pixel correction parameters in FPGA at 1-point correction mode
Comparison of parameters at different modes. (a) Multi-spectral (blue) correction parameters of multi-TDICCD at ground-based radiation calibration mode; (b) Multi-spectral (blue) correction parameters of multi-TDICCD at lab-based real-time radiation calibration mode; (c) Average response curve of single TDICCD in PAN spectrum before calibration; (d) Average response curve of single TDICCD in PAN spectrum after calibration in lab
Experimental imaging results of real-time radiation calibration in lab