April
2018
Pathfinder DVL Guide
Page 88
EAR-Controlled Technology Subject to Restrictions Contained on the Cover Page.
A brief review of Pathfinder operation may help explain the specifications listed in this section. The dis-
cussion below regarding water profiling is generally applicable to bottom track as well.
The specifications and dimensions listed in this section are subject to change without notice.
The Pathfinder emits an acoustic pulse called a PING. The seabed and scatterers that float ambiently with
the water currents reflect some of the energy from the ping back to the Pathfinder transducer. The Path-
finder uses the return signal to calculate a velocity.
The energy in this signal is the echo intensity. The echo intensity returned from the seabed is used to de-
tect the bottom. The echo intensity returned by floating scatterers is sometimes used to determine infor-
mation about the scatterers.
The velocity calculated from each ping has a statistical uncertainty; however, each ping is an independent
sample. The Pathfinder reduces this statistical uncertainty by averaging a collection of pings. A collection
of pings averaged together is an ensemble. The Pathfinder’s maximum ping rate limits the time required
to reduce the statistical uncertainty to acceptable levels.
The Pathfinder does not measure velocity at a single point; it measures its speed over the seabed, i.e. Bot-
tom Track, its speed through the water current, i.e. Water Track and current velocities throughout the wa-
ter column, i.e. Water Profile.
When bottom tracking, the Pathfinder calculates velocity data relative to itself. The velocity data has both
speed and direction information. If the Pathfinder is moving, and is within range of the bottom, it can ob-
tain a velocity from returns off the bottom. The bottom track information can be used to calculate the ab-
solute velocity of the water. The Pathfinder can get absolute direction information from a heading sensor.
When water profiling the Pathfinder measures velocities from its transducer head to a specified range and
divides this range into uniform segments called depth cells (or bins). The collection of depth cells yields a
profile. The Pathfinder produces two profiles, one for velocity, and one for echo intensity.
The following tables list the specifications for the Pathfinder. About the specifications:
1. Except where noted, these specification tables applies to typical setups and conditions. Typical
setups use the default input values for each parameter (exceptions include Pings per Ensemble
and Number of Depth Cells). Typical conditions assume uniform seawater velocities at a given
depth, moderate shear, moderate Pathfinder motion, and typical echo intensity levels.
2. The total measurement error of the Pathfinder is the sum of:
•
Long-term instrument error (as limited by instrument accuracy),
•
The remaining statistical uncertainty after averaging,
•
Errors introduced by measurement of Pathfinder heading and motion.
3. Because individual pings are independent, the statistical uncertainty of the measurement can be
reduced according to the equation:
Specifications subject to change without notice.