A model to estimate the L-band amplitude scintillation index from Swarm: the outer scale length assumption

Irregularities in the plasma density in the ionosphere affect trans-ionospheric radio signals, resulting in fluctuations in the amplitude and phase of these signals, known as amplitude and phase scintillations. We recently developed a model that relies on ESA’s Swarm constellation to estimate the amplitude scintillation index (S4), representing the plasma density irregularities affecting the L-band Global Navigation Satellite Systems (GNSS) signals. One of the main challenges for this model is the need for estimates/measurements of the outer scale length which, for operational considerations, must be available to the model independent of ground measurements as much as possible. In this paper, we show how this challenge was addressed. In particular, we rely on the combined measurements from ionosondes, GNSS scintillation monitoring receivers, Swarm 16 Hz faceplate instrument, and Rino’s formula for weak scattering scenario to solve for the outer scale wave number. Then, we develop a climatological map for the outer scale wavenumber to be utilized by the Swarm S4 model. To achieve this, we rely on conjunctions between Swarm satellites trajectories and GNSS signals paths over locations with co-located ionosondes and ionospheric monitoring GNSS scintillation receivers. We rely on models and assumptions to simplify the equations and to translate the different instruments’ measurements into their equivalent values at the phase screen height (hmF2) assumed by Rino’s formula. We detail the methodology and show the results. The outer scale length has been finally sorted into climatological in magnetic coordinates under different space weather conditions.