particle concentration in the water. An ADCP operating at
1-megahertz acoustic frequency is sensitive to zooplankton
and other particles with similar size, such as suspended oil
droplets. For instance, to understand whale migration and
feeding patterns, Woods Hole Oceanographic Institution (WHOI) researchers utilize backscatter
data from glider-mounted ADCPs to track
zooplankton location in the water column.
ters, depending on scattering conditions. The 1-megahertz
transducers allow for a small physical size and good return
signal strength over the dive profle of 1,000 meters in typical ocean scattering conditions. The instrument uses a fourbeam transducer head that creates different symmetric three-beam arrays: one that can be used on
descent and the other on ascent. By measuring during both descent and ascent, the
AD2CP provides a more complete data
set for post-processing compared to inAD2CP
struments capable of sampling only on
Since 2005, Nortek AS (Oslo, Norascent or descent.
way) has collaborated with leading
The AD2CP is equipped with a presresearchers at WHOI, the University
sure sensor and a microelectromechanof Washington, Rutgers University, Meical-systems (MEMS) tilt sensor and commorial University, University of California
pass capable of measuring throughout the
at Santa Barbara, Scripps Institution of
large pitch range that gliders experience.
Oceanography and iRobot to develop
The AD2CP is controlled over a standard
specialized ADCPs and data-processing
RS-232 interface from the glider���s main
methods to measure current velocity from gliders. In 2012,
computer, allowing easy reconfguration and download of
Nortek released the AD2CP-Glider (acoustic Doppler curdata subsets that can be transferred to shore using the glidrent profler for gliders) developed specifcally for the chaler communication systems. The interface allows the glider
lenges of measuring current velocity from gliders, such as
computer to write GPS position data and other relevant dive
small size, low power consumption and precise velocity
parameters to the AD2CP memory. Onboard memory (SD
measurements. The instrument must also be able to tolerate
card) provides large storage capacities for long-duration
frequent pressure cycling and have a high-quality orientamissions. Fast data download via an Ethernet interface is
tion sensor to resolve the pitch and roll angles during deavailable when the AD2CP is retrieved.
scent and ascent.
The AD2CP uses broadband processing for accurate veMeasurement Challenges
locity measurements. It operates at an acoustic frequency of
Despite many reasons to measure velocity from glid1 megahertz and provides a profling range of 15 to 30 meers, operational measurements have been slow to become
36 st / April 2013