General Hints and Tips

  • Ocean/lake bottom and water conditions such as salinity affect the maximum altitude at which you can operate reliably. When the maximum altitude is exceeded the Tracker 650 sends data messages with confidences set to 0.

  • Accuracy of the Tracker 650 reduces as you approach the minimum standoff (altitude), starting at about 1 meter standoff.

  • If possible the Tracker 650 should not be operated below its minimum altitude. It does not always detect going under minimum altitude and multiple reflections between the ROV and the target plane can appear to the Tracker 650 to be valid target plane detection and introduce spurious motion estimates. If you drop under the minimum altitude, try to hop up to at least 2 meters above the target plane to allow the Tracker 650 to re-acquire. In a muck environment, crashing into the muck can entrain gas bubbles and particles in the thruster wash, which may be interpreted by the Tracker 650 as sudden shifts in speed. The $DVPDX message contains an estimate of standoff so you can watch as you approach the minimum. The standoff data can optionally also be sent to the MAVlink interface and act as a virtual sounder.

  • If the Tracker 650 is not parallel to the target plane when it is moving, some of the X-Y velocity will end up in the Z velocity. For example, if you are driving your ROV parallel to a flat seabed at one meter per second, and the Tracker 650 central axis is pointed at 80 degrees down from the X axis (90 degrees would be needed to make the Tracker 650 parallel to the seabed), then the X velocity would read as 0.98 m/s, and the Z velocity would read as -0.17 m/s. If you a using a good IMU (and the orientation between the IMU frame and the Tracker 650 frame are known) and are integrating the delta positions in three dimensions, this will all work out as expected. If you are dead-reckoning only in the horizontal plane (or other plane parallel to the target plane), you can use the SET-VELOCITY-ADJUSTMENT command to fudge in a correction factor.

  • If you are sitting at the surface and using active control to keep the ROV partially out of the water, be aware that air bubbles may become entrained in the thruster wash and cause false target plane and false motion detection.

  • The Tracker 650 sometimes does not perform well in pools due to reverberations, which causes constructive and destructive interference with reflections which confuses the bottom tracker.

  • When using the Tracker 650 for position hold in areas with heavy vegetation, it is possible to get into a positive feedback loop that introduces error. If the ROV is directly over vegetation, the ROV thruster wash can cause the vegetation to move away from the ROV. This motion is picked up by the Tracker 650, and the ROV can respond by traveling in the direction of the vegetation motion. This can put the Tracker 650 over previously undisturbed vegetation, and the process repeats.

  • DVL velocities are noisier than you would expect (see here), but surprisingly, over a short span of time they regress to the mean.

  • CeruleanTracker can be used to update firmware in the Tracker 650 and to set parameters in the flash memory of the Tracker 650. Note that CeruleanTracker cannot process any of the unit's outputs into ROV position data or map references.

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