The variation in the response of solar full-disc magnetographs

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Table 1.

Overview of the instruments examined in this study.

Instrument	Period [year.month.day]	Spectral line	Image size	Pixel scale ^(a)
			[pixel]	[arcsec]
SPM	1992.11.19–2003.09.21	Fe I 8688 Å	1788 × 1788	1.14
MDI	1996.03.19–2011.04.11	Ni I 6768 Å	1024 × 1024	1.98
VSM ^(b)	2003.08.23–2009.11.27	Fe I 6302 Å	2048 × 2048	1.125
	2009.12.18–2017.10.27			1
HMI	2010.04.30–present	Fe I 6173 Å	4096 × 4096	0.504

Notes.

^(a)

The nominal spatial resolution is, for each instrument, about twice the pixel scale, though for ground-based telescopes such as SPM and VSM, this spatial resolution is never reached due to atmospheric seeing.

^(b)

The CCD camera of VSM was upgraded in the gap between 2009.11.27 and 2009.12.18, giving the change in pixel scale.

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