Bistatic HF ocean radar: Errors and limitations

Bistatic HF ocean radars are being proposed as a useful option when planning the layout of coastal stations for mapping sea surface currents. Monostatic HF ocean radar stations measure the components of the vector currents which are radially towards or away from the stations. The combination of the radials from one point on the sea surface to each station can be combined to produce the familiar surface current maps, which are the primary product from HF ocean radars. If the monostatic radars were also operating in bistatic mode, then components of the vector current are measured in the direction of the normal to each ellipse which represents a signal path length from the transmitter to the scattering point (on the ellipse) and on to the receiver. Stylised pictures of this geometry show that these surface current components are directed towards the general area of the midpoint between the transmitter and the receiver, and can be useful in reducing errors by providing extra, redundant, information in the calculation of the re-constituted vectors. Errors in determining the location of the scattering point in bistatic radar observations in some circumstances lead to degradation of the accuracy of the currents which can be detected. In this paper we consider two effects: the effect of receiver beamwidth; and the effect of receiver bandwidth.