IONOLAB-MAP: An automatic spatial interpolation algorithm for total electron content

Abstract

Investigation of the variability of total electron content (TEC) is one of the most important parametersof the observation and monitoring of space weather, which is the main cause of signal disturbance in space-basedcommunication, positioning, and navigation systems. TEC is defined as the total number of electrons on a ray path.The Global Positioning System (GPS) provides a cost-effective solution for the estimation of TEC. Due to various physicaland operational disturbances, TEC may have temporal and spatial domain gaps. Global ionospheric maps (GIMs) provideworldwide TEC with 1- to 2-h temporal resolution and $2.5^◦times5^◦$spatial resolution in latitude and longitude, respectively.The GIM-TEC with the highest possible accuracy can be obtained 10 days after the recording of the signals. Therefore,a high-resolution and accurate interpolation of TEC is necessary to image and monitor the regional distribution of TECin near-real time. In this study, a novel spatiotemporal interpolation algorithm with automatic gridding is developed for2-D TEC imaging by data fusion of GPS-TEC and GIM-TEC. The algorithm automatically implements optimum spatialresolution and desired temporal resolution with universal kriging with linear trend for midlatitude regions and ordinarykriging for other regions. The theoretical semivariogram function is estimated from GPS network data using a Maternfamily, whose parameters are determined with a particle swarm optimization algorithm. The developed algorithm isapplied to the Turkish National Permanent GPS Network (TNPGN-Active), a dense midlatitude GPS network. For thefirst time in the literature, high spatial resolution TEC maps are obtained between May 2009 and May 2012 with a 2.5-min temporal update period. These TEC maps will be used to investigate the spatiotemporal variability of the ionosphereover the diurnal and annual trend structure, including seasonal anomalies and geomagnetic and seismic disturbances overionosphere.