May
2015
WorkHorse H-ADCP Operation Manual
Page 106
EAR-Controlled Technology Subject to Restrictions Contained on the Cover Page.
A brief review of H-ADCP operation may help you understand the specifications listed in this section.
The specifications and dimensions listed in this section are subject to change without notice.
The H-ADCP emits an acoustic pulse called a PING. Scatterers that float ambiently with the water cur-
rents reflect some of the energy from the ping back to the H-ADCP. The H-ADCP uses the return signal to
calculate a velocity. The energy in this signal is the echo intensity. Echo intensity is sometimes used to
determine information about the scatterers.
The velocity calculated from each ping has a statistical uncertainty; however, each ping is an independent
sample. The H-ADCP reduces this statistical uncertainty by averaging a collection of pings. A collection of
pings averaged together is an ensemble. The H-ADCP’s maximum ping rate limits the time required to
reduce the statistical uncertainty to acceptable levels.
The H-ADCP does not measure velocity at a single point; it measures velocities throughout the water col-
umn. The H-ADCP measures velocities from its transducer head to a specified range and divides this
range into uniform segments called depth cells (or bins). The collection of depth cells yields a profile. The
H-ADCP produces two profiles, one for velocity, and one for echo intensity.
The H-ADCP calculates velocity data relative to the H-ADCP. The velocity data has both speed and direc-
tion information. The H-ADCP can get absolute direction information from a heading sensor.
The following tables list the specifications for the H-ADCP. About the specifications:
1. All these specifications assume minimal H-ADCP motion - pitch, roll, heave, rotation, and transla-
tion.
2. Except where noted, this specification table applies to typical set ups and conditions. Typical set
ups use the default input values for each parameter (exceptions include Pings Per Ensemble and
Number of Depth Cells). Typical conditions assume uniform seawater velocities at a given depth,
moderate shear, moderate H-ADCP motion, and typical echo intensity levels.
3. The total measurement error of the H-ADCP is the sum of:
•
Long-term instrument error (as limited by instrument accuracy).
•
The remaining statistical uncertainty after averaging.
•
Errors introduced by measurement of H-ADCP heading and motion.
4. Because individual pings are independent, the statistical uncertainty of the measurement can be
reduced according to the equation:
𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆
𝑈𝑈𝑈𝑈𝑆𝑆𝑈𝑈𝑈𝑈𝑆𝑆𝑆𝑆𝑆𝑆𝑈𝑈𝑆𝑆𝑆𝑆𝑈𝑈
𝑓𝑓𝑓𝑓𝑈𝑈
𝑂𝑂𝑈𝑈𝑈𝑈
𝑃𝑃𝑆𝑆𝑈𝑈𝑃𝑃
�𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑈𝑈𝑈𝑈
𝑓𝑓𝑓𝑓
𝑃𝑃𝑆𝑆𝑈𝑈𝑃𝑃𝑆𝑆