Ground flat-field calibration of a space astronomical telescope using a spatial time-sharing calibration method

Jianing Zheng; Jianing Zheng; Xu He; Xu He; Ning Zhang; Jingtian Xian; Jingtian Xian; Xiaohui Zhang

doi:10.1364/AO.498846

Applied Optics
Vol. 62,
Issue 30,
pp. 7938-7951
(2023)
•https://doi.org/10.1364/AO.498846

Ground flat-field calibration of a space astronomical telescope using a spatial time-sharing calibration method

Jianing Zheng, Xu He, Ning Zhang, Jingtian Xian, and Xiaohui Zhang

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Jianing Zheng, Xu He, Ning Zhang, Jingtian Xian, and Xiaohui Zhang, "Ground flat-field calibration of a space astronomical telescope using a spatial time-sharing calibration method," Appl. Opt. 62, 7938-7951 (2023)

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Table of Contents Category
- Imaging Systems, Image Processing, and Displays
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About this Article
History
- Original Manuscript: June 30, 2023
- Revised Manuscript: September 26, 2023
- Manuscript Accepted: September 27, 2023
- Published: October 12, 2023

Abstract

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 $\Phi {142}\;{\rm mm}$ 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.

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Data availability

Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.

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Uncertainty Source	Uncertainty (%)
L-flat calibration accuracy	0.45
P-flat calculation uncertainty	0.4
Data fusion uncertainty	0.5
Combined uncertainty	0.78

Device	Parameter
0.1 m integrating sphere	$Φ = 100 m m$ ; spherical orifice: $Φ = 38 m m$ ; uniformity: approximately 1%
Light source	OSRAM halogen lamp; electric power: 50 W; stability: $< 0.1 %$ (1 h)
Collimator	$Φ = 150 m m$ ; $F - r a t i o = 10.67$ ; $F O V = {0.8}^{\circ}$ ; spectrum transmittance: $> 80 %$ (450–750 nm)
Multipinhole mask	Etching on chrome-plated glass; $Φ = 21.5 m m$ ; $18 \times 24$ array; hole size: $40; \pm 0.5 µ m$ (central), $25 \pm 0.5 µ m$ (otherwise)
1.2 m integrating sphere	$Φ = 1200 m m$ ; spherical orifice $Φ = 500 m m$ ; nonuniformity: approximately 1.21% (within $\pm 20^{\circ}$ FOV)
2D turntable	Azimuth and pitch angle adjustment
Telescope	Nikon AF-S800: $Φ = 142 m m$ ; $F - r a t i o = 5.6$ ; CCD detector: Basler pia2400-17gm; pixel size(µm): 3.45; image pixels: $2050 \times 2448$

		RMS of Residual Map (%)
Serial Number	Maximum Deviation of Residual Map (%)	RMS1	RMS2	RMS3
1	2.86	0.558	0.565	0.720
2	2.89	0.564	0.559	0.726
3	2.83	0.586	0.588	0.701

Uncertainty Source	Uncertainty (%)
L-flat calibration accuracy	0.45
P-flat calculation uncertainty	0.4
Data fusion uncertainty	0.5
Combined uncertainty	0.78

Device	Parameter
0.1 m integrating sphere	$Φ = 100 m m$ ; spherical orifice: $Φ = 38 m m$ ; uniformity: approximately 1%
Light source	OSRAM halogen lamp; electric power: 50 W; stability: $< 0.1 %$ (1 h)
Collimator	$Φ = 150 m m$ ; $F - r a t i o = 10.67$ ; $F O V = {0.8}^{\circ}$ ; spectrum transmittance: $> 80 %$ (450–750 nm)
Multipinhole mask	Etching on chrome-plated glass; $Φ = 21.5 m m$ ; $18 \times 24$ array; hole size: $40; \pm 0.5 µ m$ (central), $25 \pm 0.5 µ m$ (otherwise)
1.2 m integrating sphere	$Φ = 1200 m m$ ; spherical orifice $Φ = 500 m m$ ; nonuniformity: approximately 1.21% (within $\pm 20^{\circ}$ FOV)
2D turntable	Azimuth and pitch angle adjustment
Telescope	Nikon AF-S800: $Φ = 142 m m$ ; $F - r a t i o = 5.6$ ; CCD detector: Basler pia2400-17gm; pixel size(µm): 3.45; image pixels: $2050 \times 2448$

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Applied Optics