Comments on “Propagation Modeling Over Irregular Terrain by the Improved Two-Way Parabolic Equation Method”

The above paper [1] is about the two-way split-step parabolic equation method (2W-SSPE) over irregular terrain, and claims that they have developed the “improved” version of the 2W-SSPE approach that has been proposed and validated by us in literature [2]-[11]. The paper [1] claims to derive the 2W-PE directly from 2D Helmholtz equation. They do this by listing and explaining equations (1)-(9). The authors needed to state that this is quite different from the formulation given in Levy´s book (reference [9] in [1]). Actually, factorization before or after does not mean anything; their equations (8) and (9) are exactly the same. As a result listing equations (1)-(9) does not mean derivation of the new two-way PE.