Ocean and Atmospheric Sci. Div. NRaD, San Diego, CA 92152-5000
To quickly obtain the wave field in parabolic wave propagation, this study sweeps the range in the largest possible range steps. Jensen and Krol [Saclanten Memorandum-72, NATO-SACLANTEN, La Spezia, Italy (1975)] obtained the truncation error of the parabolic equation that depends on the range step but did not derive the appropriate range step. The derivation was completed and it was implemented to a parabolic equation code. This study demonstrates that the truncation error of the parabolic wave equation is inadequate for the purpose of determining the maximal range step under acceptable wave-field error. This led to an analysis based on the truncation error of the wave field. It is shown that given a wave-field gain/loss of (gamma)=10 log[sub 10]|(eta)|dB, the maximal range step (Delta)r allowed is given by a formula that relates it to (eta) (that measures the wave-field truncation error), the gradients of the refraction index n (with respect to range and height) and to the wave field and its gradients. The formula had been tested successfully on the parabolic equation code.