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1.2 Conventional Methods for Measuring Cur-
rent s
Fixed point estimates of the surf- went haw usually been performed by moored
emnt meters (Beardsley et o l PO], Hdpem Ill], WeUer and Davis [lZ]). Since these
dwices must be moored at depths exceeding 20 metres, they provide little indication
of the current at the surf-. Also, b~ause of energetic high-frequency motions in the
surface layers, data produced by these -nt meters are subject to various fo- of
contamination depending on the type of instrument, the mooring codguration and
the type of environmental co%iditioGxperienced (Smith [131).
Large-scde current circulation has conventionally been mwured by the tracldng
of floating objects. Drogued or undmgued drifters are d-ed to follow the ws-
ter such that they are only rmoimdy inaueneed by wind. Since there drift- are
tracked by aircraft, radar, wsek or ~atellite, using this technique to determine the
surface current field be quite expensive and very ticonsuming (Diemand et
a1 [14],Petrie and Benor [IS]). Mar-, the spatial distribution of driftw changes
with time ar they p a through the region of intewt and/or avoid areas of net diwr-
gence. This is important, for example, in fisheries applications for the understanding
of plankton trampart.
1.3 The HF Radar Technique
Cmmbie [26] deduced experimentally that the current beneath the surface waMs of
a patch of ocean could be measured indirectly by spectrally andHng the returned
radar signal from that region. This was Later mn6nned, theoretically. by Barrick
[I] and since Crombie's initial inwstigatiorw, goad quality m-nts of surf-
currents have been obtained in North America, Europe and Australia using tm
station system (Lipa and Barrick [lq, Prandle and Ryder [IS], Jaoopaul et 01. (191).