Abstract
Abstract Each of the three satellites of the European Space Agency Swarm mission carries an absolute scalar magnetometer (ASM) that provides the nominal 1-Hz scalar data of the mission for both science and calibration purposes. These ASM instruments, however, also deliver autonomous 1-Hz experimental vector data. Here, we report on how ASM-only scalar and vector data from the Alpha and Bravo satellites between November 29, 2013 (a week after launch) and September 25, 2014 (for on-time delivery of the model on October 1, 2014) could be used to build a very valuable candidate model for the 2015.0 International Geomagnetic Reference Field (IGRF). A parent model was first computed, describing the geomagnetic field of internal origin up to degree and order 40 in a spherical harmonic representation and including a constant secular variation up to degree and order 8. This model was next simply forwarded to epoch 2015.0 and truncated at degree and order 13. The resulting ASM-only 2015.0 IGRF candidate model is compared to analogous models derived from the mission’s nominal data and to the now-published final 2015.0 IGRF model. Differences among models mainly highlight uncertainties enhanced by the limited geographical distribution of the selected data set (essentially due to a lack of availability of data at high northern latitude satisfying nighttime conditions at the end of the time period considered). These appear to be comparable to differences classically observed among IGRF candidate models. These positive results led the ASM-only 2015.0 IGRF candidate model to contribute to the construction of the final 2015.0 IGRF model.
Highlights
Every 5 years, the International Association of Geomagnetism and Aeronomy (IAGA) releases a new update of what is known as the International Geomagnetic Reference Field (IGRF) model
Worth noting is the fact that the scalar misfits for the absolute scalar magnetometer (ASM)-V parent model are nearly identical to those obtained for the vector fluxgate magnetometer (VFM) and N-VFM parent models. This reflects the fact that all three models rely on the same ASM scalar data. This result is less obvious, since the models are constrained by their respective ASM-V or VFM vector data
Using ASM-V experimental vector data acquired on board the Swarm satellites, a very valuable 2015.0 IGRF candidate model, and an valuable 2015–2020 SV test model, could be derived
Summary
Every 5 years, the International Association of Geomagnetism and Aeronomy (IAGA) releases a new update of what is known as the International Geomagnetic Reference Field (IGRF) model. The Swarm mission is the fifth Earth Explorer Mission in the Living Planet Programme of ESA (see Friis-Christensen et al (2006), for general background information) It consists of a constellation of three nominally identical satellites. It is located at the tip of the satellite’s boom, 2 m further away, and its nominal role is to provide absolute measurements of the magnetic field intensity, for both science and VFM calibration purposes. It can deliver experimental vector mode data, which are the data used here (see Léger et al (2015), for more information on the ASM experimental vector mode).
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