The method presented by Garrison et al.  is a simplification of the method presented in our uncited paper [Hernández-Pajares et al., 2006]. In this paper we extended the work (model and computations) presented by Orus et al.  (cited in the work of Hernández-Pajares et al. ), over four worldwide local networks, processed during 1 year or more, filtering out unrelated medium-scale traveling ionospheric disturbance events and using an exact analytical correction for the Doppler term (not incorporated by Garrison et al. ).