April 2018 Pathfinder DVL Guide
Page 178
EAR-Controlled Technology Subject to Restrictions Contained on the Cover Page.
The percent-good data field is a data-quality indicator that reports the percentage (0 to 100) of good data
collected for each depth cell of the velocity profile. The setting of the EX-command (Coordinate Transfor-
mation) determines how the Pathfinder references percent-good data as shown below.
EX-Command Coordinate
System
Velocity 1 Velocity 2 Velocity 3 Velocity 4
Percentage Of Good Pings For:
00xxx Beam Beam 1 BEAM 2 BEAM 3 BEAM 4
EX-Command Coordinate
System
Velocity 1 Velocity 2 Velocity 3 Velocity 4
Percentage Of:
01xxx Instrument
3-Beam
Transformations
(note 1)
Transformations
Rejected
(note 2)
More Than One
Beam Bad In Bin
4-Beam
Transformations
10xxx Ship
11xxx Earth
Note 1. Because profile data did not exceed correlation threshold (WC command).
Note 2. Because the error velocity threshold was exceeded (WE command).
At the start of the velocity profile, the backscatter echo strength is typically high on all four beams. Under
this condition, the DVL uses all four beams to calculate the orthogonal and error velocities. As the echo
returns from far away depth cells, echo intensity decreases. At some point, the echo will be weak enough
on any given beam to cause the DVL to reject some of its depth cell data. This causes the DVL to calculate
velocities with three beams instead of four beams. When the DVL does 3-beam solutions, it stops calculat-
ing the error velocity because it needs four beams to do this. At some further depth cell, the DVL rejects
all cell data because of the weak echo. As an example, let us assume depth cell 60 has returned the follow-
ing percent-good data.
FIELD #1 = 50, FIELD #2 = 5, FIELD #3 = 0, FIELD #4 = 45
If the EX-command was set to collect velocities in BEAM coordinates, the example values show the per-
centage of pings having good solutions in cell 60 for each beam based on the Low Correlation Threshold
(WC command). Here, beam 1=50%, beam 2=5%, beam 3=0%, and beam 4=45%. These are neither typi-
cal nor desired percentages. Typically, all four beams should be about equal and greater than 25%.
On the other hand, if velocities were collected in Instrument, Ship, or Earth coordinates, the example val-
ues show:
Field 1 – Percentage of good 3-beam solutions – Shows percentage of successful velocity calculations
(50%) using 3-beam solutions because the correlation threshold (WC command) was not exceeded.
Field 2 – Percentage of transformations rejected – Shows percent of error velocity (5%) that was less than
the WE command setting. WE has a default of 2000 mm/s. This large WE setting effectively prevents the
DVL from rejecting data based on error velocity.
Field 3 – Percentage of more than one beam bad in bin – 0% of the velocity data were rejected because
not enough beams had good data.
Field 4 – Percentage of good 4-beam solutions – 45% of the velocity data collected during the ensemble
for depth cell 60 were calculated using four beams.
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