It is generally accepted that scintillation observed on satellite signals that have traversed the ionosphere are caused by electron density inhomogeneities. Because the primary manifestation of scintillation is irregular signal intensity variation statistical measures have been used to characterize scintillation. However, models that characterize scintillation start with phase variations, initially without accompanying intensity variations. Effectively, scintillation starts with a scaling of path-integrated total electron density (TEC). The EM processes that convert the initiating phase structure to intensity and phase scintillation are referred to as a refraction and diffraction, although Maxwell’s equations make no distinction between refraction, diffraction, or even stochastic structure.
In two companion summaries, Scintillation Theory Revisited and Scintillation Models Revisited, we emphasized scintillation as a complex modulation initiated by the cumulative interaction of the signal with electron density structure. In the absence of stochastic scintillation structure, the signal phase responds directly to TEC. Indeed, major contributions to modeling the state of the ionosphere come from routine or targeted TEC measurements. However, definitive characterizations of ionospheric structure do not go beyond inverse-power-law spatial scale distributions borrowed from turbulence theory.
The complexity of scintillation models that incorporate structure realization generally precludes routine applications. In Structure Characterization Revisited we demonstrate a robust efficient back-propagation procedure that provides a definitive characterization of the ionosphere electron density structure causing scintillation. The structure parameters resolve the otherwise ambiguous routine S4, Prms, and ROTI measurements.
However, our preliminary results show that intercepted structure varies among three inverse power-law types, which is difficult to reconcile with simulations based on the convective instability generally believed to be the source of the structure. We suspect the evolution of convective instability structure is influenced by the state of the ionosphere, particularly traveling ionospheric disturbances. These results are presented with the hope that they can be verified and will stimulate definitive structure analysis.