An Assessment of the Current WAAS Ionospheric Correction Algorithm in the South American Region

Abstract

: The Federal Aviation Administration's (FAA) Wide Area Augmentation System (WAAS) for civil aircraft navigation is focused primarily on the conterminous United States (CONUS). In this paper, based on a limited dataset, we assess WAAS's planar fit algorithm in the equatorial region, where the spatial gradients and the absolute slant total electron content (TEC) are known to be the highest in the world. We found that in Brazil, the dominant error source for the WAAS planar fit algorithm is the inherent spatial variability of the equatorial ionosphere, with ionospheric slant range delay residuals as high as 15 m and root-mean-square (RMS) residuals for the quiet day of 1.9 m. This compares with a maximum residual of 2 m in CONUS and 0.5 m RMS. We discovered that ionospheric gradients in Brazil are at the 2 m over 100 km level. In contrast with results obtained for CONUS, we found that a major ionospheric storm had a small impact on the planar fit residuals in Brazil.