1. Hansen A, Peterson E, Walter T, Enge P (2000) Correlation structure of ionospheric estimation and correction for WAAS. In: ION NTM 2000, pp 454–463
2. Hansen A, Walter T, Blanch J, Enge P (2000) Ionospheric spatial and temporal correlation analysis for WAAS: quiet and stormy. In: ION GPS 2000, pp 634–642
3. Walter T, Hansen A, Blanch J, Enge P, et al (2000) Robust detection of ionospheric irregularities. In: ION GPS 2000, pp 209–218
4. Blanch J, Walter T, Enge P (2002) Ionospheric threat model methodology for WAAS. Navigation 49(2):103–107
5. Altshuler ES, Fries RM, Sparks L (2001) The WAAS ionospheric spatial threat model. In: ION GPS 2001, pp 2463–2467