Space weather impacts on satellite navigation signals

Kurzfassung

Space weather effects on Global Navigation Satellite Systems (GNSS) are predominately associated with degradations of L‐band (1.0–2.0 GHz) signal phases and amplitudes. Extreme solar flares are space weather events with strong influence on GNSS signal propagation at the dayside, having an impact on the quality of satellite communication and navigation. Solar flares emit electromagnetic waves in a broad wavelength spectrum including X‐rays, extreme ultraviolets (EUVs), and radio waves, causing an impact on GNSS signals through direct and indirect ways. The ionosphere with all its temporal and spatial variations is a significant threat to the precision of GNSSbased navigation services. Strong ionospheric perturbations, usually characterized by severe gradients and/or rapid changes of the electron density integrated along the used satellite-receiver links, can seriously degrade the performance of GNSS. Strong ionospheric gradients have effects on GNSS positioning services used by aviation, maritime and land users and are either caused by space weather events (e.g. Solar Flares, Solar Radio Bursts or Solar Storms) or due to special regional ionospheric conditions (e.g. at Polar or Equatorial latitudes). Solar flares can trigger an temporal ionospheric gradients on the dayside, which can cause critical situations for navigation applications and services used in aviation and maritime navigation [1]. An ionospheric storm as result of an Earth directed Coronal Mass Ejection (CME) can cause strong spatial gradients propagating from polar to equatorial latitudes lasting for hours with significant impact on accuracy and integrity of the navigation performance. Small scale ionospheric irregularities in the equatorial ionosphere can cause amplitude and phase scintillation of GNSS signals at receivers [2,3]. On the other hand, solar radio bursts, which is often associated with flares, may be composed by intense radio fluxes that exceed those observed under quiet solar conditions by several orders of magnitude. Such extreme radio burst events in the L-band frequency range can directly interfere with GNSS signals [4]. Analyzing real data sets will demonstrate the crucial impact of spatial and temporal ionospheric gradients on GNSS navigation services and applications used in the aviation, maritime and land transportation domain. Different ionospheric disturbances can be categorized with its specific features for navigation applications on the user side. We will provide information on suitable indices, which allow to rate the current ionospheric conditions on a regional level [5, 6].We will discuss how such real time indices can help to limit service outages of essential navigation services to the minimum time required.