The ionosphere in low-latitude regions is a major challenge for a satellite-based augmentation system (SBAS). The intense dynamics of this layer of the atmosphere in this part of the globe is one of the main reasons why Brazil discarded years ago the idea of deploying its own SBAS. In this article, we re-examine the ionospheric error bounds for a high-density ground station network in Brazil by updating previous work that assessed specific parameters for low latitudes, especially the ones related to the generation of the ionospheric error bounds expressed by the grid ionospheric vertical error (GIVE). Ionospheric delay maps and their respective GIVE values were generated by varying the functional model used in the interpolation of the grid points and the decorrelation parameter of the measurements for quiet and active days of the ionosphere. The resulting GIVE maps show values significantly higher than the bounds found in mid-latitudes and represent one of the main contributions of this article. An availability assessment for APV-I shows that the planar fit model with a spatial decorrelation standard deviation of 1 m provides the best availability for quiet days, while a quadratic fit with a decorrelation parameter of 2 m results in better availability for active days. Even though it would be possible to provide some service in quiet days within the area with a higher density of reference stations, the resulting availability is not ideal for a real SBAS when the ionosphere is more active.

中文翻译：

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重新检查低纬度电离层误差范围：巴西的SBAS方法

对于基于卫星的增强系统（SBAS），低纬度地区的电离层是一项重大挑战。在地球的这一部分，大气层的强烈变化是巴西几年前放弃部署自己的SBAS的想法的主要原因之一。在本文中，我们将通过更新先前的工作来重新检查巴西高密度地面站网络的电离层误差范围，该工作评估了低纬度的特定参数，尤其是那些与网格表示的电离层误差范围有关的参数电离层垂直误差（GIVE）。电离层延迟图及其各自的GIVE值是通过改变网格点插值中使用的功能模型以及电离层安静和活跃日的测量的去相关参数而生成的。生成的GIVE贴图显示的值显着高于中纬度地区，这是本文的主要贡献之一。APV-I的可用性评估表明，空间去相关标准偏差为1 m的平面拟合模型在安静日提供了最佳可用性，而去相关参数为2 m的二次拟合在活动日可获得更好的可用性。即使有可能在参考站密度较高的区域内在安静的日子提供某些服务，但当电离层较活跃时，最终的可用性对于真正的SBAS也不理想。APV-I的可用性评估表明，空间去相关标准偏差为1 m的平面拟合模型在安静日提供了最佳可用性，而去相关参数为2 m的二次拟合在活动日可获得更好的可用性。即使有可能在参考站密度较高的区域内在安静的日子提供某些服务，但当电离层较活跃时，最终的可用性对于真正的SBAS也不理想。APV-I的可用性评估表明，空间去相关标准偏差为1 m的平面拟合模型在安静日提供了最佳可用性，而去相关参数为2 m的二次拟合在活动日可获得更好的可用性。即使有可能在参考站密度较高的区域内在安静的日子提供某些服务，但当电离层较活跃时，最终的可用性对于真正的SBAS也不理想。