This is the last of three papers describing an `absolute' calibration of the GONG magnetograph using and end-to-end simulation of its measurement process. The simulation begins with a MURaM 3D MHD datacube and ends with a `synthetic magnetogram' of the corresponding magnetic field values as they would be observed by GONG. We determine a calibration by comparing the synthetic magnetic field measurements with the MURaM magnetic field values that produced them. The previous two papers have described the GONG measurement process (both instrument and data processing), our simulation of it, and the theory of magnetogram comparison and calibration. In this paper, we address some final points on calibration, combine all of this work into a set of calibration curves, and consider the results. We also review the results of the previous two papers for locality of reference. Our calibration indicates that GONG magnetograms underestimate weak flux by a factor of over 2 near disk center, but that factor decreases to about 1 as the line-of-sight approaches the limb. A preliminary investigation of the generalizability of these results suggests other instruments will be affected in a similar way. We also find that some differences in previous magnetograph comparisons are artifacts of instrumental resolution which do not reflect an intrinsic calibration difference, and the measurements are more similar than sometimes thought. These results are directly applicable to question of solar wind prediction model accuracies, particularly in the search for the cause of the common discrepancy between predicted solar wind magnetic flux at 1 AU and values measured in situ by current satellite missions.

中文翻译：

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使用端到端仪器模拟校准 GONG 磁图 III：比较、校准和结果

这是三篇论文中的最后一篇，描述了使用 GONG 磁力仪的“绝对”校准及其测量过程的端到端模拟。模拟以 MURaM 3D MHD 数据立方体开始，以 GONG 将观察到的相应磁场值的“合成磁图”结束。我们通过将合成磁场测量值与产生它们的 MURaM 磁场值进行比较来确定校准。前两篇论文描述了 GONG 测量过程（包括仪器和数据处理）、我们对其的模拟以及磁图比对和校准的理论。在本文中，我们解决了校准的一些最终要点，将所有这些工作组合成一组校准曲线，并考虑结果。我们还回顾了前两篇论文的结果以供参考。我们的校准表明 GONG 磁图低估了磁盘中心附近的弱磁通超过 2 倍，但随着视线接近肢体，该因​​子降低到大约 1。对这些结果的普遍性的初步调查表明，其他工具也会以类似的方式受到影响。我们还发现，以前磁力仪比较中的一些差异是仪器分辨率的伪影，不反映内在校准差异，并且测量结果比有时想象的更相似。这些结果直接适用于太阳风预测模型精度的问题，