Iridium Communications Satellite Constellation Data for Study of Earth's Magnetic Field. (27th July 2021)

• Record Type: Journal Article
• Authors: Anderson, Brian J.; Angappan, Regupathi; Barik, Ankit; Vines, Sarah K.; Stanley, Sabine; Bernasconi, Pietro N.; Korth, Haje; Barnes, Robin J.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 22:Number 8(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-07-27
• Subjects: geomagnetism -- Iridium Communications Inc. -- satellite constellation -- space magnetometry -- geodynamo -- magnetic field; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2020GC009515
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: Characterization of Earth's magnetic field is key to understanding dynamics of the core. We assess whether Iridium Communications magnetometer data can be used for this purpose since. The 66 Iridium satellites are in 86° inclination, 780 km altitude, circular orbits, with 11 satellites in each of six orbit planes. In one day the constellation returns 300, 000 measurements spanning the globe with <2° spacing. We used data from January 2010 through November 2015, and compared against International Geomagnetic Reference Field (IGRF‐11) to inter‐calibrate all data to the same model. Geomagnetically quiet 24‐h intervals were selected using the total Birkeland current, auroral electrojet, and ring current indices. The z ‐scores for these quantities were combined and the quietest 16 intervals from each quarter selected for analysis. Residuals between the data and IGRF‐11 yield consistent patterns that evolve gradually from 2010 to 2015. Residuals for each day were binned in 9° latitude by 9° longitude and the distributions about the mean in each bin are Gaussian with 1‐sigma standard errors of ∼3 nT. Spherical harmonic coefficients for each quiet day were computed and time series of the coefficients used to identify artifacts at the orbit precession (8 months) and seasonal (12 months) periods and their harmonics which were then removed by notch filtering. This analysis yields time series at 800 virtual geomagnetic observatories each providing a global field map using a single day of data. The results and CHAOS 7.4 generally agree, but systematic differences larger than the statistical uncertainties are present that warrant further exploration. Plain Language Summary: The shape of Earth's magnetic field is used for navigation, resource exploration, and space hazard predictions. Changes in the field provide clues to motions of the molten iron core 1, 800 miles (∼3, 000 km) deep. In recent years the magnetic poles have moved rapidly, making it especially important to track the field. Advances in satellite and launch technologies have enabled launches of satellites in greater numbers than ever before to near‐Earth space. The 66 Iridium Communications satellites, launched originally in the late 1990s and recently replaced with the Iridium NEXT constellation, have operated continuously since 1997 and are planned to continue to 2030 or beyond. Each original and NEXT Iridium satellite is equipped with a magnetometer as part of the satellite systems. We developed techniques to analyze magnetic field data from these satellites to detect small changes in Earth's magnetic field. The large number of Iridium satellites allows us to map Earth's magnetic field in just one day. This offers numerous practical and scientific benefits to understand the interior workings of our home planet. Key Points: Iridium satellite avionics magnetometers provide global coverage in measurement of Earth's magnetic field Coverage from 86°S to 86°N latitude with ∼2°longitude/latitude resolution is achieved in two hours Uncertainties as low as 3 nT in the global mapped fields are achieved for each of 260 geomagnetically quiet days from 2010 to 2015