Estimation of Polar Depletion Regions by VTEC Contrast and Watershed Enhancing

Abstract

This article presents a method for determining nearpole ionization depletion regions and troughs from GNSS VTEC maps. To define the regions, we use Image processing tools, considering the VTEC maps as grey level images. In this work, watershed segmentation is applied to determine the edges of regions, based on the flow of areas between the lowest ionization zones (< 1%) and the medium ionization regions (> 10%). In order to enhance the contrast between low-ionization regions and those with a higher relative ionization, the histogram of the maps is equalized, which increases the contrast of the VTEC maps, which is the distance between low-ionization regions and those with a higher relative ionization is increased. The use of percentile thresholds makes this method independent of hypotheses about the generation of depletions, their morphology, or about the number of depletion regions that can occur on a map. We test the performance by comparing the depletion regions identified in eight events reported in the literature under different conditions of the ionosphere. The events used as reference were measured by satellites, radar, and GNSS. The method we propose allows for real-time processing of GNSS VTEC maps. The morphology of the detected regions matches the shape that is reported in the literature.

Effects of the 12 May 2021 Geomagnetic Storm on Georeferencing Precision

“…We used the ordinary Kriging interpolation technique [64] to map the estimation of the VTEC at each ionospheric pierce point (IPP). We selected this interpolation technique to fill in the data gap of the global ionosphere TEC map and the inhomogeneous sparsity of GNSS receivers [65][66][67]. We performed the ordinary Kriging interpolation in Python with the package Kriging.…”

Method for Forecasting Ionospheric Electron Content Fluctuations Based on the Optical Flow Algorithm

“…Given the rate of ROTI map measurements was at one map per minute, we decided to apply diffusion-related ideas as a forecasting method. A similar idea was proposed in [22], for determining VTEC polar depletion regions.…”

“…An interesting feature of the OFROTI algorithm is that the True Positive Rate is very different between medium and high activity days, i.e., 11, 17 March 19,22 June 2015 and low activity days, i.e., 5 March 2015 and 13, 14 August 2018. The explanation is illustrated in Figure 12.…”

GNSS-based global ionospheric maps : real-time combination, time resolution and applications on space weather monitoring

“…Furthermore, the performance of UQRG on the most troublesome polar regions with very few GNSS receivers has been reported. UQRG is able to obtain reliable TEC estimates and captures the TEC structures even in the most troublesome polar regions Monte-Moreno et al, 2021).…”