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Preflight ground flat-field calibration is significant to the development phase of space astronomical telescopes. The uniformity of the flat-field illumination reference source seriously decreases with the increasing aperture and the telescope’s field of view, directly affecting the final calibration accuracy. To overcome this problem, a flat-field calibration method that can complete calibration without a traditional flat-field illumination reference source is proposed on the basis of the spatial time-sharing calibration principle. First, the characteristics of the flat field in the spatial domain taken by the space astronomical telescope are analyzed, and the flat field is divided into large-scale flat (L-flat) and pixel-to-pixel flat (P-flat). They are then obtained via different calibration experiments and finally combined with the data fusion process. L-flat is obtained through star field observations and the corresponding L-flat extraction algorithm, which can obtain the best estimation of L-flat based on numerous photometry samples, thereby effectively improving calibration accuracy. The simulation model of flat-field calibration used for accuracy analysis is established. In particular, the error sources or experimental parameters that affect the accuracy of L-flat calibration are discussed in detail. Results of the accuracy analysis show that the combined uncertainty of the proposed calibration method can reach 0.78%. Meanwhile, experiments on an optic system with a Φ142mm aperture are performed to verify the calibration method. Results demonstrate that the RMS values of the residual map are 0.720%, 0.565%, and 0.558% at the large-, middle-, and small-scale, respectively. The combined calibration uncertainty is 0.88%, which is generally consistent with the results of the accuracy analysis.
Preflight ground flat-field calibration is significant to the development phase of space astronomical telescopes. The uniformity of the flat-field illumination reference source seriously decreases with the increasing aperture and the telescope’s field of view, directly affecting the final calibration accuracy. To overcome this problem, a flat-field calibration method that can complete calibration without a traditional flat-field illumination reference source is proposed on the basis of the spatial time-sharing calibration principle. First, the characteristics of the flat field in the spatial domain taken by the space astronomical telescope are analyzed, and the flat field is divided into large-scale flat (L-flat) and pixel-to-pixel flat (P-flat). They are then obtained via different calibration experiments and finally combined with the data fusion process. L-flat is obtained through star field observations and the corresponding L-flat extraction algorithm, which can obtain the best estimation of L-flat based on numerous photometry samples, thereby effectively improving calibration accuracy. The simulation model of flat-field calibration used for accuracy analysis is established. In particular, the error sources or experimental parameters that affect the accuracy of L-flat calibration are discussed in detail. Results of the accuracy analysis show that the combined uncertainty of the proposed calibration method can reach 0.78%. Meanwhile, experiments on an optic system with a Φ142mm aperture are performed to verify the calibration method. Results demonstrate that the RMS values of the residual map are 0.720%, 0.565%, and 0.558% at the large-, middle-, and small-scale, respectively. The combined calibration uncertainty is 0.88%, which is generally consistent with the results of the accuracy analysis.
Zusammenfassung Wir stellen die Untersuchung der Homogenität der Strahldichte einer Ulbricht-Kugel mit großer Apertur vor, die mit einer InGaAs-Kamera im Wellenlängenbereich des SWIR gemessen wurde. Ein in der PTB entwickeltes Verfahren wird verwendet, um die Ungleichförmigkeit der relativen spektralen Empfindlichkeit der verwendeten Infrarotkamera zu korrigieren. Es werden verschiedene Konfigurationen untersucht und die Eignung der untersuchten Ulbricht-Kugel zur Charakterisierung von IR-Kameras geprüft. Es wurde festgestellt, dass die Ulbricht-Kugel eine Homogenität ihrer Strahldichte von ±1 % im integralen Wellenlängenbereich von 0,9 µm bis 1,7 µm aufweist.
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