This is the second of three papers describing an `absolute' calibration of the GONG magnetograph using an end-to-end simulation of its measurement process. In the first paper, we described the GONG instrument and our `end-to-end' simulation of its measurement process. In this paper, we consider the theory of calibration, and magnetograph comparison in general, identifying some of the significant issues and pitfalls. The calibration of a magnetograph is a function of whether or not it preserves flux, independent of its spatial resolution. However, we find that the one-dimensional comparison methods most often used for magnetograph calibration and comparison will show dramatic differences between two magnetograms with differing spatial resolution, even if they both preserve flux. Some of the apparent disagreement between magnetograms found in the literature are likely a result of these instrumental resolution differences rather than any intrinsic calibration differences. To avoid them, spatial resolution must be carefully matched prior to comparing magnetograms or making calibration curves. In the third paper, we apply the lessons learned here to absolute calibration of GONG using our `end-to-end' measurement simulation.

中文翻译：

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使用端到端仪器模拟校准 GONG 磁图 II：校准理论

这是三篇论文中的第二篇，描述了使用测量过程的端到端模拟对 GONG 磁力仪进行“绝对”校准。在第一篇论文中，我们描述了 GONG 仪器及其测量过程的“端到端”模拟。在本文中，我们考虑了校准理论和一般的磁力图比较，确定了一些重要问题和陷阱。磁力仪的校准取决于它是否保持磁通，而与其空间分辨率无关。然而，我们发现最常用于磁力图校准和比较的一维比较方法将显示具有不同空间分辨率的两个磁力图之间的显着差异，即使它们都保持通量。文献中发现的磁力图之间的一些明显差异可能是这些仪器分辨率差异的结果，而不是任何固有的校准差异。为了避免它们，在比较磁图或制作校准曲线之前，必须仔细匹配空间分辨率。在第三篇论文中，我们使用我们的“端到端”测量模拟将这里学到的经验应用于 GONG 的绝对校准。