An Inverse Diffraction Technique for Scaling Measurements of Ionospheric Scintillations on the GPS L1, L2, and L5 Carriers to Other Frequencies

C.S. Carrano, K.M. Groves, S.H. Delay, P.H. Doherty

Abstract:	To predict the impact of ionospheric scintillations on communications, navigation, and space radar systems it can be useful to simulate the RF conditions under which these systems must operate. GNSS satellites broadcast radio signals that can be monitored by receivers on the ground to specify scintillations at multiple frequencies in the L band range. In this paper, we describe an inverse diffraction technique for mapping the deterministic structure of GPS scintillations measured at the L1, L2, and L5 frequencies to other frequencies. In the case of weak scatter, a statistical theory that describes how the S4 index scales from one frequency to another is well established (Rino, Radio Sci., 14, 1135, 1979). However, this statistical scaling breaks down when the S4 index at either frequency saturates due to multiple scatter effects. The inverse diffraction technique can be used under both weak and strong scatter conditions, and it works as follows. The complex signal fluctuations on the ground are back-propagated up to ionospheric altitudes to infer an equivalent phase screen. Forward-propagation through a wavelength-scaled version of this screen provides a realization of the complex fluctuations at the desired operating frequency. Using 50 Hz measurements of C/No and phase fluctuations on the GPS L1, L2, and L5 carrier signals from Brazil, we validate the technique by predicting scintillations on each GPS carrier signal from the others. We quantify the accuracy of the results by calculating the Euclidean norm of the difference between predicted and measured signals. We find the results to be most accurate for equatorial scintillations when the relative velocity between the penetration point and zonal drift is directed across the magnetic field lines. The reason for this is that the propagation calculations are restricted to the plane of the satellite scan, and when this scan is across highly field-aligned irregularities all structure with spectral content at the Fresnel scale is resolved.
Published in:	Proceedings of the 2014 International Technical Meeting of The Institute of Navigation January 27 - 29, 2014 Catamaran Resort Hotel San Diego, California
Pages:	709 - 719
Cite this article:	Carrano, C.S., Groves, K.M., Delay, S.H., Doherty, P.H., "An Inverse Diffraction Technique for Scaling Measurements of Ionospheric Scintillations on the GPS L1, L2, and L5 Carriers to Other Frequencies," Proceedings of the 2014 International Technical Meeting of The Institute of Navigation, San Diego, California, January 2014, pp. 709-719.
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