For the past 20 years, state of the art geomagnetic core field models have relied heavily on magnetic measurements made from space-based instrumentation. These models have revealed rapid global magnetic field variations on sub-decadal timescales originating in Earth’s core. With the end of the CHAMP mission in 2010 and the launch of Swarm in late 2013, there has been a 3-year gap in high-quality satellite measurements of the geomagnetic field. Geomagnetic field models have therefore relied on ground observatory data to fill in this gap period. However, ground observatories are unable to provide a truly global picture of the core field and its temporal changes. Many satellites in operation carry vector fluxgate “platform” magnetometers for attitude control, which can offer an alternative to relying on ground observatory measurements during the gap period. However, these instruments need to be carefully calibrated in order to provide meaningful information on Earth’s core field. Some previous studies attempted to calibrate such instruments with a priori geomagnetic field models. This approach has several disadvantages: (1) errors in the model will introduce errors in the calibration parameters, and (2) relying on an a priori model may not be feasible in the post-Swarm era. In this paper, we develop a novel approach to build a time-dependent geomagnetic field model from platform magnetometer data, by co-estimating their calibration parameters with the internal field parameters. This method does not require an a priori geomagnetic field model, but does require a dataset of previously calibrated data. We use CHAMP, Swarm, and ground observatory measurements to supply this dataset, and incorporate platform magnetic measurements from DMSP and Cryosat-2 during the gap years. We find that the calibration parameters of DMSP and Cryosat-2 can be reliably estimated, and these missions provide meaningful information on rapid core field variations during the gap period.

中文翻译：

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地磁场和在轨磁通门磁力计校准参数的联合估计

在过去的 20 年里，最先进的地磁核心场模型严重依赖于空间仪器的磁测量。这些模型揭示了起源于地核的次年代时间尺度上全球磁场的快速变化。随着 2010 年 CHAMP 任务的结束和 2013 年底 Swarm 的发射，高质量的地磁场卫星测量出现了 3 年的空白。因此，地磁场模型依靠地面观测数据来填补这一空白期。然而，地面观测站无法提供核心场及其时间变化的真正全球图景。许多运行中的卫星携带矢量磁通门“平台”磁力计用于姿态控制，这可以提供在间隙期间依靠地面观测站测量的替代方案。然而，这些仪器需要经过仔细校准才能提供有关地球核心场的有意义的信息。之前的一些研究试图用先验的地磁场模型校准此类仪器。这种方法有几个缺点：（1）模型中的错误会在校准参数中引入错误，（2）依赖先验模型在后 Swarm 时代可能不可行。在本文中，我们开发了一种新方法，通过将其校准参数与内部场参数共同估计，从平台磁力计数据构建时间相关地磁场模型。该方法不需要先验地磁场模型，但需要先前校准数据的数据集。我们使用 CHAMP、Swarm 和地面天文台测量来提供此数据集，并在间隔年期间合并来自 DMSP 和 Cryosat-2 的平台磁测量。我们发现可以可靠地估计 DMSP 和 Cryosat-2 的校准参数，并且这些任务提供了关于间隙期间快速核心场变化的有意义的信息。