Note on: 'EMLCLLER-A program for computing the EM response of a large loop source over a layered earth model' by N.P. Singh and T. Mogi, Computers & Geosciences 29 (2003) 1301-1307

Singh and Mogi (2003) presented a forward modeling (FWD) program, coded in FORTRAN 77 called “EMLCLLER”, which is capable of computing the frequency-domain electromagnetic (EM) response of a large circular loop, in terms of vertical magnetic component (Hz), over 1D layer earth models; computations at this program could be performed by assuming variable transmitter-receiver configurations and incorporating both conduction and displacement currents into computations. Integral equations at this program are computed through digital linear filters based on the Hankel transforms together with analytic solutions based on hyper-geometric functions. Despite capabilities of EMLCLLER, there are some mistakes at this program that make its FWD results unreliable. The mistakes in EMLCLLER arise in using wrong algorithm for computing reflection coefficient of the EM wave in TE-mode (rTE), and using flawed algorithms for computing phase and normalized phase values relating to Hz; in this paper corrected form of these mistakes are presented. Moreover, in order to illustrate how these mistakes can affect FWD results, EMLCLLER and corrected version of this program presented in this paper titled “EMLCLLER_Corr” are conducted on different two- and three-layered earth models; afterwards their FWD results in terms of real and imaginary parts of Hz, its normalized amplitude, and the corresponding normalized phase curves are plotted versus frequency and compared to each other. In addition, in Singh and Mogi (2003) extra derivations for computing radial component of the magnetic field (Hr) and angular component of the electric field (Eϕ) are also presented where the numerical solution presented for Hr is incorrect; in this paper the correct numerical solution for this derivation is also presented.