Characteristics of electron content between GPS and IRNSS altitudes studied around the northern anomaly crest location over Indian longitude sector

One of the newly launched satellite navigation systems is the Indian Regional Navigation Satellite System (IRNSS) operating at L5 and S band and providing position determining with an accuracy of 10 m over the Indian subcontinent and 1,500 km beyond. Collocation of this constellation, containing three geostationary and four geosynchronous satellites, with GPS over a common ionospheric volume at certain times of the day provides a unique opportunity to estimate the highly sparse electron content existing between the GPS and geostationary/synchronous orbital altitudes. These values of electron contents, though an order of magnitude less than the diurnal maximum of TEC, could account for significant proportion of postmidnight TEC around the northern crest of Equatorial Ionization Anomaly in the Indian longitude sector. Such measurements are of importance when efforts are being made to achieve subcentimeter level position accuracies. Data recorded using a tri-band IRNSS receiver and dual-frequency GPS receiver from Calcutta during April-June 2019 have been analyzed to calculate electron contents along a specific look angle containing GPS as well as IRNSS satellite at different times of the day. Diurnal maximum values of 4–5 TECU are noted for electron contents bound within the altitudes of GPS and IRNSS. Spatial distribution of such electron content shows diurnal maximum around 14:00–15:00 LT over subionospheric swath of 20–22°N with 80–82.5°E and 87–90°E.