Some technical questions of our customers

Hi Cerulean team,

I have compiled some questions of BRS Robotica Submarina customers, hope you can help me answer them!

Can an external Depth/Pressure sensor be used to aid positioning?
Can we use Receiver in Responder mode? (not 1s ping, but to reply only when a electrical signal is sent via tether)
Is it possible to increase the receiver depth rate to 300m?
How often do I need to recalibrate to achieve accuracy 0,5% (or closer) of water depth? What are the main obstacles to increase the accuracy?
Is it possible to input a Sound velocity profile, or an average sound velocity to the application?
Does the application include an external navigation screen? Is it possible to input a georeferenced dwg/dxf drawing?
Any sample video ?

Best Regards,
— Vagner Martini.

Hello VMartini and Happy Holidays!

Let us take a look at these and we will get back to you.

Hello Vagner Martini,

We have some people traveling for the holidays – we will answer your questions by Jan 2nd

Thank you for your patience!

Hi @dennysb

Sure, no problem! Thank you for your support!

Best wishes for New Year!

— Vagner Martini.

Hello Vagner, and Happy New Year!

Please find answers to the questions you have previously posted.

1) Can an external Depth/Pressure sensor be used to aid positioning?

Yes, but the computations need to be done separately. Use the ROVL’s slant range and the external depth sensor’s depth estimate to compute the horizontal range. See also the math examples in the user manual.

2) Can we use the Receiver in Responder mode? (not 1s ping, but to reply only when an electrical signal is sent via a tether)

No. The reason has to do with automatic gain control which is needed to improve angular accuracy. Substantial re-engineering would be needed to convert to a poll/response system.

3) Is it possible to increase the receiver depth rate to 300m?

We are testing such a unit. One issue is that the hardened mechanical components interfere with the sound field in some orientations. We should have a better idea how feasible a 300m receiver is by March 2020.

4) How often do I need to recalibrate to achieve accuracy 0,5% (or closer) of water depth? What are the main obstacles to increase accuracy?

None of the values output by the USBL are related to water depth. Is this question related to slant range (the point-to-point distance between the receiver and transmitter)? For slant range accuracy, as noted in the user manual, we recommend calibrating for clock drift when initially putting the system into service and about every three months after that. If this is done, we expect a typical slant range accuracy drift of under 2m/hour. If you know the average speed of sound in your water body, you can get a slight improvement in accuracy by loading that value into the receiver.

5) Is it possible to input a Sound velocity profile or an average sound velocity to the application?

The receiver can be given an average sound speed, which it will store in non-volatile memory. The factory-default default speed of sound is 1484 m/s.

6) Does the application include an external navigation screen? Is it possible to input a georeferenced dwg/dxf drawing?

The ROVL Application is not intended to be a workhorse user interface or operating tool. It is meant as a basic tool to test your system components and get familiar with them. For everyday system operation we recommend using our QGroundControl plug-in found on this link.

Hi @dennysb, thank you for your reply.

I understand the accuracy drift is based on crystal drift rate. Can it be minimized by often calibrating? Being the two elements in the same circuit, wouldn’t be possible to create an automated “on the fly” calibration, let’s say, every 10min?

Hi @VMartini

The calibration procedure matches the frequency of the crystal in the transmitter with the crystal in the receiver. They are not on the same circuit.

The crystals were selected for low drift and to have similar thermal drift. They should give you relatively good stability – in our testing; the range usually drifts less than a meter per hour. If better range accuracy is required, the Cerulean ROVL may not be your best option.