Sentinel V SC and RT Operation Manual
September
2017
EAR-Controlled Technology Subject to Restrictions Contained on the Cover Page.
Page 265
At the start of the velocity profile, the backscatter echo strength is typically high on all four beams. Under
this condition, the ADCP 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 ADCP to reject some of its depth cell data. This causes the ADCP to calcu-
late velocities with three beams instead of four beams. When the ADCP does 3-beam solutions, it stops
calculating the error velocity because it needs four beams to do this. At some further depth cell, the ADCP
rejects all cell data because of the weak echo. As an example, let us assume depth cell 60 has returned the
following percent-good data.
FIELD #1 = 50, FIELD #2 = 5, FIELD #3 = 0, FIELD #4 = 45
In BEAM coordinates, the example values show the percentage of pings having good solutions in cell 60
for each beam based on the Low Correlation Threshold. Here, beam 1=50%, beam 2=5%, beam 3=0%, and
beam 4=45%. Note that these are neither typical nor desired percentages. Typically, you would want all
four beams to 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 was not exceeded.
Field 2 – Percentage of transformations rejected – Shows percent of error velocity (5%) that was less than
the error velocity setting. Error velocity has a default of 2 m/s. This large error velocity setting effectively
prevents the ADCP 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.
Table 42:
Percent-Good Data Format
Binary
Byte
Field
Description
1,2
ID Code
Stores the percent-good data identification word (00 04h).
3
Depth cell 1,
Field 1
Stores percent-good data for depth cell #1, field 1. See above.
4
Depth cell 1,
Field 2
Stores percent-good data for depth cell #1, field 2. See above.
5
Depth cell 1,
Field 3
Stores percent-good data for depth cell #1, field 3. See above.
6
Depth cell 1,
Field 4
Stores percent-good data for depth cell #1, field 4. See above.
7-max
Depth cell 2 –
max
These fields store percent-good data for depth cells 2 through maximum # of cells
(depending on the ReadyV Setting), following the same format as listed above for
depth cell 1.
Only the averaged PD0 files created by
Velocity
will have Percent Good data.
