General Usage

The Tracker 650 operates by bouncing three narrow conical sonar beams off a target plane (often the target plane is the seabed or bottom of a body of water). The Tracker 650 measures the frequency of each return beam.

If any of the transmit/receive elements are moving with respect to the target plane, that return beam frequency is shifted due to the Doppler effect. By measuring the frequency shift, we can calculate the relative velocity between each transmit/receive element and the target plane. Depending on how the sensor is angled with respect to the target plane, and the direction of motion, each beam may sense a different velocity. We also measure the orientation of the sensor with respect to the target plane. All this information is run through an Extended Kalman Filter (EKF), which outputs sensor velocity in all three axes relative to the sensor. If the sensor is fixed reasonably rigidly to your ROV and is lined up with the ROV's cardinal axes, the velocities then also apply to the ROV.

Since the sensor beams are angled from a target plane - to - line normal, the target plane does not provide as good a return as you might get from sounding sonars that are pointed straight at the target plane. Best overall performance comes when the sensor head is operated in a parallel position relative to the target plane. As the head is tilted more and more off parallel, one or more of the returns become weaker and weaker. While the Tracker 650 can operate temporarily with as few as one beam locked on the target plane, performance is degraded. Take-away: keep it as parallel to the target plane as you can while operating.

Tracker 650 with notional cones showing the sensor -3dB patterns

The following are a few scenarios to illustrate how you might use the Tracker 650. The scenarios are not exhaustive, nor are they necessarily mutually exclusive.