Vessel mounting an Aquadopp

I understand that the profilers are designed for fixed mounting, but is it possible, when used with an RTK-GPS to track vessel speed and direction, to use the profilers (as opposed to the permanently mounted systems) in vessel mounted mode? I am sure that I have heard of this being done successfully, but can find no reference to it on Nortek sites.

I have seen reference to the AWAC being used in this way, with VMCP software and bottom tracking firmware. I can't find reference to this software or procedure.

We are in the market for a number of ADCPs and want to  try to cover as many bases as possible.

kep

Dear Kep

I am afraid our vessel mounted profilers is a well kept secret - even for our distributors. I am not quite sure why but I suppose we have always been a little scared of the support requirements for current profilers mounte on vessel.  

Anyway, here is the story:

a) Nortek has been delivering software that combines the older 0.5 MHz and 1.5 MHz Nortek Doppler profilers (NDP), GPS and heading sensors since 1998. We call this software SurveyP and it has been well proven in 24/7 operations on at least 30 different vessels   Most of these are professional vessel operating in deep water but some are used coastal research.

b) In 2002, we introduced a firmware version with bottom track in our 1 MHz AWAC model.  We also modified the output so it would work with the SurveyP software. As a result, the AWAC (now also including the 600 kHz unit) can be used both with bottom track correction and GPS/Heading correction.  We have sold quite a few of these - this time mostly for coastal research - and they are used quite extensively by the organization that have decided to go this route." />'>

I hope this is of some help.  Again, I apologize that we keep all this to ourselves .  It is obviously time to dedicate a WEB page to a more detailed description of our vessel mounted systems.

Best regards,

Atle Lohrmann

Thanks for the information Atle.  Two questions to clarify:

Is SurveyP software the same as VMCP software?

Do you mean that SurveyP can not be used with your current range of Aquadopp profilers (eg the 2MHz)?

Regards

Kevin

Dear Kep

Yes, the VMCP and the SurveyP software is the same.

The data format expected by the software only works with the AWAC system so no, unfortunately it does not work with the Aquadopp profiler.

Best regards,

Atle Lohrmann

Moved to Vessel mounted forum - Admin

Atle.  1) Would you (or somebody else) be able to tell me what sort of minimum working water depths are possible with the AWAC/Bottom tracking/Survey P solution? 2) Do you have any provision for shallow water depth modes (eg modes 11 and 12) as offered by RDI instruments?

Thanks

kep

Kep, The AWAC VM systems can measure to one cell plus blanking in depth, i.e. If cell size is set to 0.5m and blanking is 0.5m the system will measure 1 cell of current in a depth of down to 1.5m.
Nortek has not implemented, the mode 11 and 12 type sampling stategy in this system, and uses time averaging to get a low standard deviation. You can however, reduce the standard deviation by reducing the number of cells and the maximum bottom track depth. The unit will ping faster and this will increase accuracy. " />'>

Just to clarify: The Nortek AWAC is the base of the Nortek vesselmount system with bottomtrack. A normal AWAC can be converted into a VM AWAC by purchasing a new firmware. This firmware is unique for each AWAC and must be bought seperately for each unit. The customer can switch between AWAC and VM AWAC themselves.

If a bronze unit is required, this is called the Vessel Mount Current Profiler (VMCP). This unit only has three transducers, and is made to be used only on vessels.

In addition to the firmware, the customer will need to purchase software to run the VM system. This software is called SurveyVM (but is sometimes refered to as SurveyP).

Just to add to the confusion " />'>  Nortek has previously made a vessel mount system based on the old NDP platform. This was called the Vessel Mount NDP and had a similar software called SurveyNDP. This is no longer in general release, but is of course, supported.

Hi,

I am a little confused by these posts.  Is it possible to use an aquadopp as a vessel mounted profiler when using RTK GPS?

Or do you need the AWAC to do this?

I assume that this is alot easier with the AWAC, but as i already have the use of a Nortek Aquadopp and RTK GPS i would like to know if this is still possible?

Many thanks
Roger

Dear Roger

I can understand how this can be confusing - our work with vessel mounted systems is not well documented.

The Survey software comes in two versions.  One works with the older NDP hardware and it assumes that you have a GPS (and heading) system to subtract the vessel speed.  The other version works with the AWAC electronics (referred as a VM-CP in this context) and it works if (and only if) the bottom tracking firmware is installed in the AWAC hardware.  This version of the software works both with bottom tracking and GPS/Gryo correction of the data.

I am afraid there is no version of the software that works with the Aquadopp profiler or any other Nortek instrument.  Sorry about that.

Best regards,

Atle Lohrmann

So if i cannot use my Aquadopp profiler boat mounted while motoring, i plan to take profiles at multiple sites while stationary using the Aquadopp either:

- boat mounted while anchored
- or mounted on an anchored buoy that is deployable

I am assuming that the buoy mounted would swivel less on the anchor and therefore be more stationary.

But how can i counteract for any Aquadopp movement caused by surface waves?

It could be possible to correct for it using the tilt meter and compass data, yet their frequency will be too sparse to measure small scale movement. Shall i average the velocities over a larger amount of time?

Also, do you have any information or suggestions on the design of the buoy mounting, bearing in mind that it needs to be deployable from a small (5.5 m) boat, and therefore relatively small in comparison to those buoy mountings in your gallery.

Much appreciated. Mal

Hi Mal,

Ship profiles
If you are planning on using a boat/ship to take profiles, then you may want to put it in XYZ instead of ENU so that the influences from the hull, engine, etc. do not influence the profiler's internal compass.  Instead use the ship's gyro.  If you boat is non-iron then you should be safe as long as the profiler is away from the engine.

The option of making the measurments from a buoy may be a better bet.  There are less influences from the ship with regard to compass and currents.


Surface Waves Effects
It is true that surface waves will effect the current measurements; the good news is that you can rectify this.

The first issue is the local currents created by the waves themselves (orbital currents under a wave).  These local currents have the same period as the passing waves, and the mean current over one cycle is zero.  This means if you average over one cycle then you will remove the wave induced currents and be left with the mean currents which is what you are most likely interested.

The best way to average out wave currents is to select an average interval that is long relative to the expected wave period.  If you expect waves to be no more than 10 seconds then you will be fine with the default average interval of 60 seconds.

The second issue with surface waves is the motion of the buoy/profiler.  The effects of changing tilt and heading can be accounted for by sampling the tilt and compass sensors faster.  This is exactly what is done when you select the Buoy Mounted option under the mounting choices.  As long as the buoy is not violently dancing on the ocean surface, the measured orientation may be used when we convert from beam coordinates to ENU coordinates.  Furthermore, the fact that you will be averaging over a duration of 60+ seconds will help remove any bias created by motion of the buoy.


Buoy Configurations
I unfortunately do not have any suggestions for the buoy design at this moment. A buoy that is deployable from a small boat obviously has to be small itself and therefore it begins to become challenging in terms of meeting the data collection objectives.  Small details like a lot of buoyance means a larger mooring and counter weight (to keep the buoy vertical).

Nortek does offer an Inline Mounting Frame with a swivel for these types of applications.

best regards,
Torstein