The ionospheric medium is the primary source of error for signals from the Global Positioning System (GPS) satellites. Modeling ionospheric effects is one of the main challenges in developing accurate and reliable services for Space-Based Augmentation Systems. The Mapping Function (MF) and the estimation of the model coefficients are an essential parameter in the aspects of ionospheric modeling. In the present study, a Planar Fit (PF) model is considered to model the ionospheric Total Electron Content (TEC). The Ionosphere observations (GPS-TEC) obtained directly from the GPS receiver at Koneru Lakshmaiah Education Foundation (KLEF)-Guntur (16.44° N, 80.62° E) station and are used as reference values for comparison during the period 2015. The PF model is two-fold: first, the ionospheric line-of-sight TEC is converted into vertical TEC (vTEC) based on the Modified Mapping Function (MMF), and secondly, the PF coefficients are estimated based on the Gram–Schmidt Orthogonalization (GSO). The performance of the model is tested under quiet and disturbed ionosphere conditions and for different months of the year. The PF model values are in good agreement with the GPS-TEC values for the scenarios considered. The Average Absolute Error (AAE) and Root Mean Square Error (RMSE) values are maximum in equinoxes (March and October) and moderate in winter (January and December) and minimum in summer months (July and August). The PF model is adequate for characterizing the low-latitude ionospheric characteristics in different space weather conditions. The results would support towards the development of regional ionosphere models for navigation users under the GAGAN/NavIC system in India.

中文翻译：

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低纬度地区基于修正映射函数和 Gram-Schmidt 正交化的电离层 TEC 改正建模

电离层介质是全球定位系统 (GPS) 卫星信号的主要误差来源。电离层效应建模是为天基增强系统开发准确可靠服务的主要挑战之一。映射函数（MF）和模型系数的估计是电离层建模方面的重要参数。在本研究中，考虑使用平面拟合 (PF) 模型来模拟电离层总电子含量 (TEC)。直接从 Koneru Lakshmaiah 教育基金会 (KLEF)-Guntur (16.44° N, 80.62° E) 站的 GPS 接收器获得的电离层观测值 (GPS-TEC) 用作 2015 年期间比较的参考值。 PF 模型有两个方面：第一，基于修正映射函数（MMF）将电离层视线TEC转换为垂直TEC（vTEC），其次，基于Gram-Schmidt正交化（GSO）估计PF系数。该模型的性能在安静和受干扰的电离层条件下以及一年中的不同月份进行了测试。PF 模型值与所考虑场景的 GPS-TEC 值非常吻合。平均绝对误差 (AAE) 和均方根误差 (RMSE) 值在春分点（3 月和 10 月）最大，冬季（1 月和 12 月）中等，夏季（7 月和 8 月）最小。PF 模型足以表征不同空间天气条件下的低纬度电离层特征。