
Pathfinder DVL Guide
April
2018
EAR-Controlled Technology Subject to Restrictions Contained on the Cover Page.
Page 127
Bit g controls the output of a data type with sensor source for parameters needed for Doppler calculations.
This data indicates what sensors data were used for parameters of the Doppler calculation. This may be
different than that specified by the EZ (
) and EY (
EY – Sensor Source Override for
Doppler Parameters
) commands depending on whether a sensor failed. Setting bit g to one causes this
data type to be output. See Table 46 for a definition of this data type.
Correction for vertical speed of sound for Phased Arrays
Bit ‘f’ of the #EE command must be set to 1 for the firmware to do the internal computations required to
output the correct horizontal and vertical velocities.
If the user has set a fixed speed of sound for their phased array DVL using EZ and EC (or using the default
of 1500 for EC) and wants to correct the vertical velocity using the actual speed of sound, the correction
formula is
𝑉𝑉
𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎
=
𝑉𝑉
𝑜𝑜𝑎𝑎𝑎𝑎𝑜𝑜𝑎𝑎𝑎𝑎
∗
�
1
𝐶𝐶
𝑎𝑎𝑢𝑢𝑢𝑢𝑢𝑢
2
−
1
4
𝐶𝐶
0
2
�
1
𝐶𝐶
𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎
2
−
1
4
𝐶𝐶
0
2
Where
C
user
is the fixed speed of sound that was set by the user
C
0
= 1536m/s
C
actual
is the speed of sound from a SOS sensor or computed from measured temp and salinity
V
output
is the vertical velocity output by the DVL
For C
user
=1500 and C
actual
= 1450 the correction factor is 0.9569 while the ration of the speeds of sound
would give 0.9667 and error of 1% for the corrected speed of sound if the ratio were used instead of the
above equation.
Derivation:
By design, for our phased array ADCPs, the actual beam angle in the water is given by
sin(
𝜃𝜃
) =
𝑐𝑐
2
𝑐𝑐
0
Where c
0
= 1536meters/sec.
Therefore
cos(
𝜃𝜃
) =
�
1
− 𝑠𝑠𝑠𝑠𝑠𝑠
2
(
𝜃𝜃
) =
�
1
−
�
𝑐𝑐
2
𝑐𝑐
0
�
2
If velocity is purely vertical, the velocity solution for a given Doppler frequency f
d
is given by
𝑣𝑣
=
𝑓𝑓
𝑑𝑑
∗ 𝑐𝑐
2
𝑓𝑓
0
cos (
𝜃𝜃
) =
𝑓𝑓
𝑑𝑑
∗ 𝑐𝑐
2
𝑓𝑓
0
�
1
−
� 𝑐𝑐
2
𝑐𝑐
0
�
2
=
𝑓𝑓
𝑑𝑑
2
𝑓𝑓
0
�
1
𝑐𝑐
2
−
1
4
𝑐𝑐
0
2
Where f
0
is the system frequency.
Taking the ratio of two vertical velocity solutions determined using different values for c obtains the equa-
tion at the top.