Estimation of Ionospheric Spatial Gradient in Mid Latitudes by Satellite-Pair Method

The aircraft's navigation system routinely makes use of the Global Navigation Satellite System (GNSS) during numerous phases of a flight. A primary concern is Ionospheric Gradients, which might impact the global positioning system's positional accuracy. Data from a single GNSS reference station is required for Ionospheric Spatial Gradient estimation using the well-known Time-Step Method. Temporal decorrelation faults are one type of inaccuracy that accompany the Time-Step Method. Conversely, the Station-Pair technique uses two GNSS reference stations that are closely separated to estimate the Spatial Gradient. When GNSS stations are far apart, the Station-Pair Method is ineffective in determining delay gradients in ionospheric plasma at short baselines. An attractive alternative is Satellite-Pair Method which uses observations from a single GNSS reference station. Satellite-Pair approach compares the Ionospheric delays of two satellites that are being monitored by the same receiver at the same time. GNSS data for the year of January to December 2021 was obtained from the mid latitude stations p502 (Imperial County, California) with Geographical Latitude and Graphical Longitude 32°58'55.2"N and 115°25'19.2"W and p509 (Holtville, California) with Geographical Latitude and Graphical Longitude 32°48'40.18"N and 115°22'48.95"W located in California, USA. The maximum Ionospheric Spatial Gradient for disturbed day (15 June 2021) using Satellite-Pair Method is found to be 4.6047 mm/100km, whereas for Existing Time-Step and Station-Pair Methods are 2.2089 mm/100km and 1.8859 mm/100km.The Spatial Gradients are found to be occurred mostly between 2000hrs to 2200hrs UT.