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This paper presents an algorithm to estimate regional ionospheric total electron content (TEC) and TEC gradients.In this study,the ionospheric vertical TEC (VTEC) at an ionosphere piercing point (IPP) in a local area is represented by contributions from the VTEC at other IPPs in the local area and spatial gradients of TEC along both latitudinal and longitudinal directions.By differencing the TEC between each pair of observable IPPs,linear equations of local TEC gradients can be established if only first order and second order TEC spatial derivatives in the TEC representation are retained.The TEC gradients obtained from these linear equations are then combined with VTEC of observable IPPs to generate regional TEC maps.The algorithm is tested using a single GNSS receiver located on the campus of Tongji University over a 24-hour period.The TEC values obtained from the algorithm are compared with that from the polynomial-based regional ionospheric TEC model constructed using data from 13 stations in Yangtze River Deltaarea and also with estimations generated from the IGS global ionosphere maps (GIM).The results show that the average difference between TEC values generated from a single receiver using the TEC gradient-based algorithm and from 13 stations using the polynomial-based regional TEC model is around 1 TECU,and the standard deviation of the differences is about 1.5 TECU.Also,the average difference between TEC values calculated from the proposed TEC algorithm and from GIM is about 0.5 TECU,and the standard deviation of the differences is nearly 1.6 TECU.The results demonstrate that the proposed TEC gradient-based method has the potential to produce accurate regional TEC maps for precise positioning and for ionospheric monitoring using measurements from only a single receiver.The algorithm can be easily modified to incorporate other multi-GNSS measurements such as GLONASS,Beidou System and Galileo to further improve precision.