Orientation

Hi

The tilt sensor does not work if a standard Aquadopp is oriented horizontally.  When the tilt sensor does not work, the compass does not work because the compass is based on the outputs of a 3-axis magnetometer and the tilt sensor.

In other words, with the system lying on the side you cannot collect meaningful data in ENU (East, North, Up) coordinates. You can still collect data in XYZ coordinates - just remember that the XYZ coordinates is tied to the head so that it changes orientation as you mount the system horizontally.  I believe there are drawings in the manual that illustrate this point. " />'>

Best regards,

Atle Lohrmann

PS It is possible to permanently change the orientation of the tilt sensor.  This requires that the system comes back to the factory to have another tilt sensor installed.  We also do a full calibration of the tilt + magnetometer as part of the procedure.  

Quote

I have a question regarding the orientation of the Aquadopp "mooring head". Although this Aquadopp is designed for vertical orientation, is it possible to use it horizontally and  if so, what are the concerns if we use it that way?

Hi

Would it then be OK to mount a Vector horizontally and have the probe pointing down vertically?  I realise this would put the tilt sensor and compass off, but would the XYZ data collected still be correct without a tilt sensor?

Regards,
Jonathan Stewart.

Dear Jonathan

Yes, it will " />'>

In this case, the instrument collects data in the coordinate system of the probe.  With some luck, probe 1 has a mark on so you can identify the X-axis.  A positive Z-velocity is toward the probe.

Best regards,

Atle Lohrmann

Hi

After a lot of tests in laboratory, we found that is necesary to install vectors before the start of the deployment. If this condition fails, for example if there is a delay in the transportation to the study site, the compass begin with an orientation that could not be the desired. We have data taken in this situation, instruments began to collect data before we installed it, in fact the systems must be work vertical and they were horizontal while we carring it. Is there any way to correct this probe and sensor had the same orientation once intalled.

Rafael

 

Hi Rafael,

The compass, pitch and roll sensors are continuously updated so the instrument will use the appropriate compass heading once it is deployed. While carrying it (I'm assuming out of the water) you'll probably get very unusual readings, but there will only effect measurements the Vector takes out of the water and you're probably not interested in those anyway. 

If you have a cabled probe head, make sure you know the orientation of it relative to the compass if using ENU data.

Thanks,

we made a few more tests. In continuos sampling the compass seems to be not updated while in burst mode it works well. Our deployments were in burts mode, then the data must be correct (after installation).

How often the compass should be updated in continuos sampling? is it just at the start of the deployment?

Hi Rafael,

You can read more about this in the manual, but what you need to be aware of is the update of the up/down orientation of the system. In order to calculate correct ENU coordinates there is an up/down sensor in the Vector as a part of the tilt sensor. And if you run continuous measurements this orientation is only established at the time when the deployment starts. In burst sampling mode the Vector checks for up/down orientation at the beginning of each burst interval. This is one of the reasons why we recommend burst sampling for autonomous deployments.

During velocity measurements the compass data are updated once every second, both for burst mode and in continuous mode. If the Vector collects data with the wrong up/down orientation you will not be able to find out exactly what the true heading, pitch and roll of the instrument was. If the Vector was in a fixed position during the deployment the best thing might be to convert the ENU coordinates to XYZ using the conversion you can find here on the forum. If you can not use the XYZ coordinates instead of ENU I guess you will have to do a test where you deliberately make sure the up/down orientation is set as in the actual deployment and position the Vector until you get the same reading as during the deployment. Keeping the Vector in that fixed position you then restart the measurement and then you can read the correct values for heading, pitch and roll. These values then have to be used when converting from XYZ back to ENU. If the position during the actual deployment was fixed this is actually not as bad as it sounds. On the other hand, if it was not fixed I would say that it is worse...

Best regards,

Sven Nylund

Hi people of Nortek,

I would like to mount a remote head Vector with it's probe orientated horizontally, collecting data using XYZ coordinates.

When selecting the velocity range setting do I now consider the vertical velocity range as my horizontal velocity range? For example, the Vector will be towed at a speed of 1.2m/s, do I need to use a velocity range of 2m/s (vertical velocity range = 1 m/s) or 4m/s (vertical velocity range = 1.5 m/s).

Kind regards,

Mairéad

I would like to mount a remote head Vector with it's probe orientated horizontally, collecting data using XYZ coordinates.

When selecting the velocity range setting do I now consider the vertical velocity range as my horizontal velocity range?

 

Yes, you'll want to make sure what the Vector software reports as the Vertical Velocity Range is large enough for your expected horizontal velocities. If you're expected horizontal velocities are 1.2 m/s than the 4 m/s Nominal Velocity Range sounds like what you need to use.

 

P.J.