Wayfinder DVL Guide
P/N 95P-6001-00 (October 2020)
EAR-Controlled Technology Subject to Restrictions Contained on the Cover Page.
Page 13
Acoustic Integration Considerations
Interference from other acoustic and electromagnetic devices can cause velocity and direction bias. In
extreme cases, interference may prevent the Wayfinder from operating. It is possible to avoid inter-
ference by using a suitable triggering scheme. This is particularly recommended if the other device is op-
erating within the bandwidth of the Wayfinder receiver (in some cases up to 40% of the carrier frequency
of the Wayfinder) or if the other device has a harmonic component that is within the Wayfinder fre-
quency receive bandwidth. Initiating a well-conceived triggering scheme (triggering the interfering de-
vice, the Wayfinder, or both) will keep the interfering device from operating during the Wayfinder’s
transmit and receive period. It is important to note that the TRDI receivers have 90 to 110 dB of
gain, which for the sake of clarity is greater than 100,000 times of voltage amplification.
Table 3.
Transmit and Receive for the Wayfinder DVL
Wayfinder System
Carrier Frequency
Transmit & Receive Bandwidth
600 kHz
614400 Hz
38.4 kHz (6.25%)
Data and Timing Considerations
Data Screening
Wayfinder measurements suffer from occasional data outliers which, although rare, can still be far more
frequent that would be expected from a normal (Gaussian) probability function. To prevent the navigation
system from giving undue weight to data outliers, it is important to screen the Wayfinder data to detect
and reject them.
Data outliers are often the result of ambient data environmental factors. The Wayfinder DVLs have sev-
eral internal routines to detect and account for the false data described. Unless the bottom is detectable,
and the correlation value is above a threshold criterion, bottom track velocity will be marked Not a Num-
ber (NaN). The presence of fish in one or more beams will also cause data outliers. The Wayfinder also
screens for fish using the information in the intensity data for all four beams.
If all four beams pass these screening tests, the Error Velocity (representing the redundant information
among the four beam velocities) is calculated and its magnitude compared to a threshold as an additional
screen. Measurements exceeding this Error Velocity threshold will be rejected.
To keep the Wayfinder errors as independent as possible from ping to ping, the Wayfinder does not screen
for unreasonably abrupt changes in altitude or velocity. These kinds of screens are most appropriately
performed at the front end of a navigation system. An isolated abrupt change in altitude is most likely an
outlier (fish or other false target) that should be rejected, whereas a step function with a persistent final
altitude might be real (a cliff or a transition from a vehicle hull to the real bottom, for example). A robust
algorithm will reject the isolated data outlier while quickly recovering from a persistent step. Similar
screening can be done on velocities.
Three-Beam Solution
The Wayfinder screens the velocity data by comparing the magnitude of the Error Velocity to a threshold.
The Error Velocity has redundant information among the four beam velocities. A three-beam solution is
produced if, on a particular ping, only three beams have good data, and in that case only, error velocity
screening cannot be performed. The Wayfinder still computes a four-beam solution with error velocity
screening on all pings where all four beams have good data. There are operating circumstances where due
to the bottom slope and/or pitch only three beams can have adequate reflection from the bottom, while
the fourth beam is not. The three-beam solution makes it possible to operate in such severe environments.
