Regional Mapping of Small‐Scale Equatorial Ionospheric Irregularities Using Swarm Echo Satellite Measurements

We propose a novel approach to produce regional maps of small‐scale scintillation‐causing irregularities using a single satellite. To construct the maps, we employ several ionospheric GPS indices, including total electron content, high‐resolution ROTI, and S4, calculated from the Swarm Echo GPS Attitude, Positioning, and Profiling Experiment Occultation (GAP‐O) receiver with its antenna pointed upward. GAP‐O's high‐sample‐rate observations enable irregularities as small as 320 m to be resolved. We present two case studies in which we compare the maps with in situ measurements of irregularities and simultaneous vertical TEC maps obtained from the ground. In situ measurements of net current onto the external surface of the Imaging and Rapid‐scanning Ion Mass Spectrometer sensor on board Swarm Echo were utilized to quantify plasma density fluctuations. Then, we apply the method to synthetic data to illustrate the efficacy of the method. Modeling results show that the irregularity maps can determine the horizontal geo‐locations of small‐scale irregularities, though with significant uncertainties in the cross‐track direction (east‐west). As Swarm Echo traverses different altitudes, these maps provide additional information on the altitudinal distribution of plasma fluctuations. This technique facilitates a better understanding of the morphology of scintillation‐causing irregularities, which are challenging to map from ground‐based receiver arrays alone. Plain Language Summary We propose a novel approach to mapping of the horizontal distributions of ionospheric irregularities, or variations in ionospheric electron density, using the Swarm Echo satellite while it traverses the equatorial ionosphere at altitudes between 330 and 1,280 km. Swarm Echo carries a GPS receiver capable of simultaneously sampling signals from multiple GPS satellites at a rate of 50 measurements per second, corresponding to spatial scale sizes as small as 320 m. A high‐rate, in situ measure of relative plasma density complements the GPS integral measurements. The method is tested using synthetic data, demonstrating that irregularities can be localized along Swarm Echo's trajectory with high resolution and accuracy. Performance in the direction perpendicular to the satellite's path is poorer, but properties including general position and large‐scale gradients can be recovered. Comparison with maps of vertical total electron content obtained from ground measurements shows that combining the