GPS particle detectors track space radiation over two decades
Cross calibration combines data from 25 satellites The post GPS particle detectors track space radiation over two decades appeared first on Physics World .
Researchers in China have successfully cross-calibrated radiation detectors on 25 GPS satellites, utilizing data collected over a two-decade period. This study has resulted in a comprehensive record of the relativistic electron flux impinging on Earth's atmosphere. The GPS system employs signals from satellites to pinpoint positions on Earth with high precision, and each satellite carries a radiation detector.
These detectors enable scientists to monitor space radiation changes, particularly high-energy electrons originating from the Sun. The electron flux fluctuates with the solar cycle, which lasts approximately 11 years and involves variations in sunspots, solar flares, and coronal mass ejections. Accurate satellite design and operation require understanding this electron flux, yet challenges persist in fully utilizing the data due to discrepancies in measurement values between satellites, particularly during low flux periods.
Additionally, not all satellites employ identical detectors – two different instruments have been utilized. To overcome this, researchers in China cross-calibrated the particle detectors on these 25 GPS satellites, generating a calibrated dataset spanning two solar cycles (2000–2020). This process involved analyzing two distinct measurements from the detectors – the differential electron flux at 2 MeV from a specific direction and the integral electron flux from all directions at energies exceeding 2 MeV.
Accounting for Earth's magnetic field effects was crucial, using the concept of magnetic local time to address the magnetic poles' offset from the planet's rotational axis. The team employed the NS59 satellite as a reference, as its detector consistently generated data from 2004, overlapping with other satellites in the study. Statistical analyses enabled the integration of data from 24 of the 25 satellites, although one detector presented issues and should not be used.
The researchers assert that their technique can be extended to cross-calibrate detectors at other energies, with 14 differential and 29 integral channels available for analysis. They have already applied similar methods to cross-calibrate GPS data with measurements from China's BeiDou positioning system and observations from NASA's Van Allen Probes. The research findings are published in Satellite Navigation.
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