The extraction of polarization features is the key to the further application of remote sensors. For conventional remote sensing, the evaluation method of polarization characteristics is polarization sensitivity, which needs to be obtained through polarization testing. For polarization remote sensing, it is necessary to obtain the polarization characteristics of the instrument through polarization calibration. Polarization correction requires not only the measurement of the polarization characteristics of the target, but also the calibration of the polarization characteristics of the instrument, and the ultimate goal is to eliminate the polarization response of the instrument. Therefore, it is necessary to carry out research on polarization feature extraction and correction technology. This paper mainly discusses the difficulties and technical approaches of current polarization feature extraction and correction, analyzes the key technologies and related progress, and provides important reference value for further improving the quantitative acquisition of target information.
KEYWORDS: Diffraction, Segmented mirrors, Telescopes, James Webb Space Telescope, Error analysis, Optics manufacturing, Sensors, Signal detection, Visibility, Signal processing
Two-Dimensional Dispersion Fringe Sensing (TDDFS) is an efficient method for coarse phasing of segmented mirrors. Modeling and simulations based on double-aperture diffraction are used to study dispersion fringe in two directions. In the dispersion direction, the nonlinear least squares fitting method is used to extract the piston error. The theoretical capture range is ±96μm which is verified compared with the simulation results, and the detection accuracy can be reached to λ/10. However, the nonlinear least squares fitting method cannot effectively detect piston errors within one wavelength. In the diffraction direction, the principal maximum extraction method is used to measure the piston error, which is suitable for the piston error detection with a small range within one wavelength. In order to reduce the influence of the extraction error of the center line, we propose a corrective method. The results show that the accuracy of the modified principal maximum extraction method can reach 30nm. The two methods can effectively meet the requirements of the piston detection of the large-aperture segmented mirror telescopes.
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