Groundwave propagation predictions for the littoral environment (GRAPPLE)

A new engineering, propagation prediction tool, GRAPPLE, applicable between 10 kHz and 30 kHz has been described that offers significant benefits over the ITU recommended model, particularly for scenarios within the littoral environment. The ability to produce area coverage predictions with relative ease will aid the process of frequency management. As greater accuracy in the calculation of co-ordination distances can be achieved then the groundwave mode of propagation can be exploited through frequency reuse. There has been a concentrated effort in the HF community for developing high data rate modems, Jorgenson et al. (2000) reported trials from a shore station to users over a sea surface providing reliable communications at 24 kbps. They concluded that for non-fading channels, such as the groundwave, that data rates up to 64 kbps were not unreasonable. It is suggested that, as the groundwave mode offers a more stable propagation environment than the skywave, it is more suited to exploitation by high data rate systems.