ADCP Data Collection during
the SBI Spring Cruise,
Healy is equipped with two Acoustic Doppler Current Profilers (ADCPs),
band 150 kHz (BB150) and an ocean surveyor 75 kHz (OS75).
The OS75 was newly installed during the
recent dry-docking period early this spring and enhancements were made
systems to maximize their capabilities.
Roughly speaking, the higher frequency BB150 unit is capable of
vertical resolution while the lower frequency OS75 unit is capable of
range. During the cruise the configurations of both units were varied
the capability of different setups.
conditions were most favorable, the BB150 had a range of 150 to 200m
OS75 had a range of over 400m.
Both units returned good data when
The biggest item
affecting the quality of the data was breaking ice.
Under those conditions only occasional pings
In their sensitivity to
the noise and vibration associated with ice breaking, the ADCPs were no
different than the other acoustic devices on the ship.
Since the ship spent most of the cruise in
heavy ice conditions, he distribution of good data is heavily biased to
periods when the ship was on station with the result that while the
coverage looks very good, the spatial coverage appears intermittent.
Data processing has not reached the stage
where we are able to determine to what extent we can extract reasonable
data from the ice breaking periods.
have we been able to determine whether there are differences in data
that depend on the severity of ice breaking.
Another factor affecting the data coverage was the shallowness
of the Chukchi Sea
The draft of the ship plus the quiescent
interval before the ADCPs can start to acquire the data from each ping
that the shallowest bins start at about 20m, a significant fraction of
water depth over the shelf (~40m).
Special techniques are required to extract useable data from the
region before interference from the bottom limits the range.
Maximizing the data under both ice breaking
and shallow water conditions will be one of the major tasks during the
A preliminary data processing
methodology was developed during the cruise that enables a presentation
data that have been roughly calibrated and undergone some quality
The results should be adequate for
determining the overall velocity structure during the cruise.
Further refinements will probably make only
adjustments to the velocities.
the magnitude of the adjustments is hard to anticipate, it should be
The biggest modification
is to the BB150 unit when we are able to determine the speed of sound
However, the lack of
knowledge of the sound velocity in the well has been roughly taken into
during bottom-track calibration and since temperature is fairly
constant in the
fresh water/antifreeze mixture in the transducer well, big changes in
data are not anticipated.
The ADCP velocity data distributed
at the end of the cruise have been averaged into half-hour by 10 meter
bins from each instrument.
are contained in two large ASCII data files, HY0201_BB150_ADCP_Vel.dat
HY0201_OS75_ADCP_Vel.dat, in which the velocity profiles are listed,
with the date, time and position, by time interval. Data bins where the
velocity data did not pass the preliminary editing process are
These data are also presented
in color contour plots of eastward and northward current components in
files: HY0201_BB150_Vel.tif and HY0201_OS75_Vel.tif, respectively.
In addition to these basic data
products, velocity contours are also presented for the West and East
For these plots, the data
were averaged into 5 km radial segments from the beginning of each
The standard deviations of the
eastward and northward binned velocities are also presented in separate
for each ADCP.
The velocity contour
plots for the transects are presented in: HY0201_BB150_WHS_UV.tif,