Abstract
Abstract. The accuracy and availability of satellite-based applications, like Global Navigation Satellite System (GNSS) positioning and remote sensing, crucially depend on the knowledge of the ionospheric electron density distribution. The tomography of the ionosphere is one of the major tools for providing links to specific ionospheric corrections and studying and monitoring physical processes in the ionosphere and plasmasphere. In this work, we apply an ensemble Kalman filter (EnKF) approach for the 4D electron density reconstruction of the topside ionosphere and plasmasphere, with the focus on the investigation of different propagation models, and compare them with the iterative reconstruction technique of simultaneous multiplicative column normalized method plus (SMART+). The slant total electron content (STEC) measurements of 11 low earth orbit (LEO) satellites are assimilated into the reconstructions. We conduct a case study on a global grid with altitudes between 430 and 20 200 km, for two periods of the year 2015, covering quiet to perturbed ionospheric conditions. Particularly the performance of the methods for estimating independent STEC and electron density measurements from the three Swarm satellites is analysed. The results indicate that the methods of EnKF, with exponential decay as the propagation model, and SMART+ perform best, providing, in summary, the lowest residuals.
Highlights
The ionosphere is the charged part of the upper atmosphere extending from about 50 to 1000 km and going over in the plasmasphere
The different methods are presented with the following colour code: blue for the method rotation, green for the method exponential decay, light blue for the method rotation with exponential decay and magenta for NeQuick and red for simultaneous multiplicative column normalized method (SMART)+
We assess three different propagation methods for an ensemble Kalman filter approach in the case that a physical propagation model is not available or is discarded due to the computational burden. We validate these methods with independent slant total electron content (STEC) observations of the satellites of GRACE and Swarm A and with independent Langmuir probes data of the three Swarm satellites
Summary
The ionosphere is the charged part of the upper atmosphere extending from about 50 to 1000 km and going over in the plasmasphere. In the presented work, we concentrate on the modelling of the topside part of the ionosphere and plasmasphere and utilize only the space-based STEC measurements. We introduce an ensemble Kalman filter (EnKF) to estimate the topside ionosphere and plasmasphere based on space-based STEC measurements. We discretize the ionosphere and the plasmasphere below the GNSS orbit height by 3D voxels, initialize them with electron densities calculated by the NeQuick model and update them with respect to the data. We present different methods for how to perform the propagation step and assess their suitability for the estimation of electron density For this purpose, a case study of quiet and perturbed ionospheric conditions in 2015 is conducted to investigate the capability of the estimates to reproduce assimilated STEC and to reconstruct independent STEC and electron density measurements.
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