the regional multibeam/sidescan/subbottom survey was being conducted, a
pole-mounted 600kHz acoustic doppler current profiler (ADCP) was
deployed to measure instantaneous current profiles beneath the vessel
wherever she went. The aim was to make measurements of the currents
field through the bay as a function of the M2 and K1 tides.
Nevertheless, it should be realised that during the ~ 40 day survey
window, the tides ranged from neaps to springs, from dominantly diurnal
to dominant semi-diurnal (see adjacent figure).
Nevertheless, this data acquisition could be carried out at no addition
survey costs and allowed us to establish the typical direction and
magnitude of currents in the Bay during the ebb and flood periods.
Using this data we designed a series of 12.42 hour (M2 tide period)
repetitve oceanographic sections. The exact survey sequenceand data
density, was dictated by weather and seafloor data
acquisition (80m line spacing).
In an attempt to randomise the observations as a function of phase of
tide, we tried to survey every second line and return to do the
intermediate lines ~ 7 days later (when the pahase of the tide would
have shifted by ~ 1/2 M2 tidal period). This novel sampling approach
ended up being redundant as the time disruptions due to
mechanical and weather delays ensured that the survey preceded in a
pseudo-random manner anyway.
The animation above show depth average current vectors obtained, sorted
by phase of the M2 tide. Should there be interst, we can put the source
current data online in an appropriate manner.