Solar energetic particle events create radiation risks for aircraft, notably single event effects (SEEs) in microelectronics along with increased dose to crew and passengers. In response to this, some airlines modify their flight routes after automatic alerts are issued. At present these alerts are based on proton flux measurements from instruments on-board satellites, so it is important that contemporary atmospheric radiation measurements are made and compared.

This paper presents the development of a rapid-response system built around the use of radiosondes equipped with a radiation detector, Zenith, which can be launched from a Met Office weather station after significant solar proton level alerts are issued. Zenith is a compact, battery-powered solid-state radiation monitor designed to be connected to a Vaisala RS-92 radiosonde which transmits all data to a ground station as it ascends to an altitude of ~33 km. Zenith can also be operated as a stand-alone detector when connected to a laptop, providing real-time count rates. It can also be adapted for use on unmanned aerial vehicles.

Zenith has been flown on the Met Office Civil Contingency Aircraft (MOCCA), taken to the CERN-EU high energy Reference Field (CERF) facility for calibration and launched on a meteorological balloon at the Met Office's weather station in Camborne, Cornwall, UK. During this sounding, Zenith measured the Pfotzer-Regener maximum to be at an altitude of 18 - 20 km where the count rate was measured to be 1.15 counts s-1 cm-2 compared to 0.02 counts s-1 cm-2 at ground level.