Equatorial scintillation calculations based on coherent scatter radar and C/NOFS data

Abstract

During its transit through a region of equatorial ionospheric irregularities, sensors on board the Communication/Navigation Outage Forecasting System (C/NOFS) satellite provide a one‐dimensional description of the medium, which can be extended to two dimensions if the structures are assumed to be elongated in the direction of the magnetic field lines. The C/NOFS scintillation calculation approach assumes that the medium is equivalent to a diffracting screen with random phase fluctuations that are proportional to the irregularities in the total electron content, specified through the product of the directly measured electron density by an estimated extent of the irregularity layer along the raypaths. Within the international collaborative effort anticipated by the C/NOFS Science Definition Team, the present work takes the vertical structure of the irregularities into more detailed consideration, which could lead to improved predictions of scintillation. Initially, it describes a flexible model for the power spectral density of the equatorial ionospheric irregularities, estimates its shape parameters from C/NOFS in situ data and uses the signal‐to‐noise ratio S/N measurements by the São Luís coherent scatter radar to estimate the mean square electron density fluctuation 〈ΔN2〉 within the corresponding sampled volume. Next, it presents an algorithm for the wave propagation through a three‐dimensional irregularity layer which considers the variations of 〈ΔN2〉 along the propagation paths according to observations by the radar. Data corresponding to several range‐time‐intensity maps from the radar is used to predict time variations of the scintillation index S4 at the L1 Global Positioning System (GPS) frequency (1575.42 MHz). The results from the scintillation calculations are compared with corresponding measurements by the colocated São Luís GPS scintillation monitor for an assessment of the prediction capability of the present formulation.

A global ionosphere scintillation propagation model for equatorial regions

“…These inhomogeneities are substructures of bubbles, which may reach dimensions of several hundreds of kilometers as can be seen from radar observations (Costa et al 2011). These bubbles present a patchy structure.…”

Equatorial scintillation predictions from C/NOFS Planar Langmuir Probe electron density fluctuation data

“…The first study will identify high-elevation passes of the satellite over São Luís and compare results from scintillation index S 4 measurements by the TBB receiver at its three operation frequencies with predictions by: (i) the model briefly described in the previous section [3]; and (ii) a purely space-based phase-screen scintillation model [5], [6]. The second model will use a properly scaled version of electron density fluctuations directly measured by the Planar Langmuir Probe on board the C/NOFS satellite to represent the random phase of the screen.…”

“…The main missing information in the calculations is the variation of the irregularity strength along the ray path. While the previous model (i) represents this variation through a mapping of S/N measurements by the São Luís coherent scatter onto mean square electron density fluctuations [3], this representation will be performed by the space-based phase-screen model (ii) in an approximate fashion (to keep its independence from ground-based data). Therefore, the results from this comparative study, which are not adversely affected by time and west-to-east evolution of irregularity structures, will characterize the prediction capability of the space-based model, being important to relate each set of measured and calculated S 4 values to the position of the C/NOFS satellite with respect to those of intense irregularities, displayed by corresponding RTI maps from the INPE São Luís Observatory.…”

“…As an independent testing tool of the above models, the authors [3] developed an algorithm for the propagation of satellite signals through a three-dimensional irregularity layer which solves a parabolic approximation to the wave equation, valid when partial reflections are negligible. The layer is subdivided into multiple statistically homogeneous and independent thin slabs, and the Huygens-Fresnel diffraction theory is repeatedly applied to each of them.…”

On whistler mode wave scattering from density irregularities in the upper ionosphere

“…We assume that the correlation function 〈 δn ( x 1 , z 1 ) δn ( x 2 , z 2 )〉, which defines the statistical spectral density w ( p , q ), has the following form: Hence, . Function w p ( p ) is normalized in an usual way [see Costa et al , 2011] such that 〈 δn ( x , 0) δn ( x , 0)〉 = 〈 δn 2 〉. Here (〈 δn 2 〉) 1/2 should be considered as an amplitude of irregularities and a small parameter of the method of successive approximations.…”