Recently, VHF (Very High Frequency) radars have frequently been used for measuring the flow velocity field on the coast, as they enable the velocity distribution for exceedingly wide regions to be obtained simultaneously. This paper describes the results of an examination of the inference of a radar installed on board a steel vessel, where a VLCC (Very Large Crude-oil Carrier) was used for the experiments. Even if the characteristics of the received waves, called ¿antenna pattern¿ here, is deformed, it is possible to estimate the arrival direction of the radio waves in specific regions. The results imply the possibility of measuring the flow velocity distribution by means of VHF radars on board vessels.
Knowing the surface current of the sea is important for the management of marine transportation, environmental issues, and ocean resources. The ocean current has been traditionally measured by specific velocity meters, such as floating buoys, magnetic current meters, and so on. Such methods are categorized under ¿point measurement¿, reflecting the fact that they are capable of measuring the current at specific points. Furthermore, the ADCP (Acoustic Doppler Current Profiler) has recently become a very popular instrument with regard to the ¿line measurement¿ method, or the so-called one-dimensional measurement method (Appel et al. 1991). It is a powerful non-contact tool using supersonic waves which provides the velocity profile along a specific line, particularly the velocity distribution in depth direction. In addition, PIV (Particle Image Velocimetry) has been developed for the purpose of the so-called ¿plane measurement¿, which is sometimes also referred to as two-dimensional measurement (Aida et al. 2002). PIV is very useful for obtaining the velocity distribution in extremely wide regions simultaneously. However, it is not effective at night or in bad weather, as its performance strongly depends on its ability to acquire a clear image of the sea surface.
