Specifications

Channel Master Operation Manual
P/N 95B-6001-00 (January 2005) page 121
Beam Coordinates: Profile data is reported as referenced along each beam
(i.e. no coordinate transformation is performed upon the raw data).
Beam Spreading: The extent to which the main lobe of energy generated
by a transducer fans out, or spreads as an acoustic wave front, with distance
from the transducer. This is proportional to λ/d where λ is the wavelength
of sound generated and d is the diameter of the transducer. Note: this is
why ADCP transducer diameter increases with decreasing operating fre-
quency (and increasing wavelength).
Bin (Depth Cell): A measurement within a profile, generally equivalent to a
single-point current meter on a mooring.
Bin Mapping (Depth Cell Mapping): When the ADCP is tilted; the meas-
urements taken at equal distances along each beam are no longer in the
same horizontal layer of water. For example, in the image below the tilted
ADCP bins do not line up horizontally, they are offset by one bin. In this
case the tilted ADCP will offset the bins on the “right” beam by one bin in
order to line them up horizontally with the bins on the “left” beam before
combining the measurements to compute the velocity.
Blank Zone: The area near the head of an ADCP in which no measure-
ments are taken. This is usually the minimum distance required to avoid
collecting data that is potentially contaminated by ringing, but is some-
times extended for other reasons (e.g. to begin measurement well beyond
the flow influence of a mounting structure).
Bottom Discharge: When using an ADCP to measure river discharge, it is
not possible to measure all the way to the bottom (due to sidelobe contami-
nation and the finite resolution of the depth cells). In order to get an accu-
rate approximation of the total discharge, the flow in this area must be esti-
mated and included, usually by extrapolating the measured velocities to the
bottom using a power curve fit.
Bottom Track: In moving platform applications where the bottom is within
range of the ADCP or DVL, a special ping can be transmitted to measure
the Doppler shift of the signal return from the bottom. If the bottom is not
moving, this measurement is a very accurate measurement of the platform
velocity. For ADCPs this velocity is typically used to extract the true water
velocity profile from the measured velocity profile (by removing the vehicle
motion from the measurements). For DVLs, this IS the desired velocity.