
April
2018
Pathfinder DVL Guide
Page 28
EAR-Controlled Technology Subject to Restrictions Contained on the Cover Page.
Water Tracking Parameters
The parameters for DVL Water Tracking feature is either preset in the instrument default mode or user
defined (see the
and Table 21, page 108). The user-defined Water Track ping layer is used
unless the layer comes within 20% of the water boundary (sea floor for down-looking systems; surface for
up-looking systems). As the user-defined Water Track ping layer comes within 20% of the boundary
(Figure 15, B), the layer compresses in size until the minimum water-mass layer size is reached. No Water
Track ping will be sent when the boundary exceeds the 20% limit (Figure 15, C).
The water-mass layer is operational only if BP > zero and BK > zero.
Current Profiling
The Pathfinder DVL has optional firmware configurations that enable the instruments to measure current
velocities in the water column. The DVL, as with all TRDI ADCPs, measures current by dividing the veloc-
ity profile into uniform segments called depth cells (depth cells are often called bins). Each depth cell is
comparable to a single current meter. Therefore, a DVL velocity profile is like a string of current meters
uniformly spaced on a mooring (Figure 16).
Thus, we can make the following definitions by analogy:
Depth cell size = distance between current meters. Number of depth cells = number of current meters
Figure 16.
DVL Depth Cells for Current Measurements
The water profile data used for current measurements includes the four different kinds of standard profile
data shown below. These data types can be incorporated to varying degrees, depending on the user re-
quirements and mission.
•
Velocity
– as measured from the Doppler shift of the individual beams of the DVL/ADCP.
•
Echo intensity
– A byproduct of the ADCP system. Sometimes used to measure relative sedi-
ment, plankton or other suspended particle quantities.
•
Correlation
– an indicator of the fidelity of the ping echo, used for QA.
•
Percent good
– percent of pings that meet specified quality thresholds used for QA.