The attenuation of the electromagnetic wave travelling along the sea
surface depends on the radar frequency and on the conductivity (salinity)
of the water. The table gives some estimates of working ranges for selected
radar frequencies and water salinities.
The values for 'Ropt' and 'Rmin' have
been derived from 'Modern Radar Techniques, COLLINS, Editor: M.J.B. Scanlan,
Chapter 5, Author: E.D.R. Shearman'.
The radar frequency must be selected carefully, taking into account the use
of the radio spectrum by communication services. Long-term observations of
the radio band coverage using a spectrum analyzer should be done before
selecting a radar frequency. The working ranges given in the table are based
on a clear frequency without interference. In any case, a
radio transmit license
is required prior to operating the HF radar.
The values for the highest possible range resolution of the radar are limited
by the frequency bandwith (the width of the gaps in the radio spectrum)
available at the different radar frequencies. They are derived from
observations of the radio spectrum.
Finally, it must be checked that the Bragg-scattering ocean waves
(PBragg and WBragg exist in area to be monitored.
This may be critical in shallow areas, where long ocean waves 'feel' the
sea buttom and are attenuated.