Geoscience Reference
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Figure 3.7 General view of the experimental site at Lake George. The platform and hut containing
logging equipment are shown on the right. The measurement bridge extends toward the left. Figure
is reproduced from Babanin et al. ( 2001 ) by permission of American Geophysical Union
viewed using a video camera. In addition, the records were electronically 'marked' by an
observer who manually recorded visual occurrences of breaking. All the measurements
were synchronised. Using this integrated system, it was possible to inter-relate the visual
appearance of the water surface in any sequence of individual video frames and the acoustic
signature of breaking waves at that time, together with the wave-height properties measured
by the directional array at the breaking location.
An anemometer mast, accommodating three wind probes at 10m and 5
65m elevations
above the water surface (two cup anemometers measured one-minute mean and two-second
gust wind speeds and one wind vane measured wind directions), was erected 10m from
the platform beyond the end of the measurement bridge to avoid disturbing the air flow.
Another anemometer mast, accommodating five wind probes at four heights closer to the
surface (four cup anemometers and a wind vane), was set 6m to the side of the bridge to
ensure undisturbed airflow for these lower anemometers.
A total of 26 records of all the measured variables, relevant for studying wave breaking,
taken over the period October-December 1997, were processed, and Table 5.2 summarises
their parameters. Selection of records was based only on the requirement of relatively
constant wind speed.
The wind speed U 10 and wind direction were measured very close to 10m above the
water level by the uppermost wind speed and wind direction sensors on the anemometer
mast. The wind probes were Aanderaa Instruments wind speed sensor 2740 and wind direc-
tion sensor 3590. Slow changes in the water depth in Lake George caused only small vari-
ations in the position of the sensors over the surface, and corresponding adjustments in the
U 10 speed were made on the basis of the wind profiles obtained with the anemometer mast.
.
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