Some questions about AWAC AST 600 kHz wave deployment

Good day

I am re-posting this under the wave measurements threat:

We are planning our first deployment with our new AWAC AST 600 kHz and I have a few questions.

The AWAC will be on deployed in a subsurface float at 40 m, in a total water depth of 80 m. We are expecting to measure large (> 5 m) long period (10 sec) waves for a duration of 2 months, during our winter storm season.

I have selected the following deployment plan:

Currents (standard tab) - Profile interval: 1800 s, Number of cells: 25, Cell size: 2 m.

These settings were selected so that the instrument can profile past the surface, but I get a warning that the profiling range is greater than 40 m. Is is necessary to 'shoot' past the surface or will it create errors in my data? 

What about the magnetic variation? The area has an offset of -24 degrees. Do I include this in the setup or during post-processing and how does it influence the directional wave measurements?

Waves (standard tab) - No of samples: 1024, Sampling rate: 1 Hz, Interval: 5400 s, SUV mode selected

Do I have to tick the 'waves - static mode' box to activate the AST function?  Should I use the default values here?

As far as processing of the waves data go,

Do I enable onboard wave processing?

Where can I get the Nortek ExploreWave Software mentioned in the AWAC manual (p 59)? Do I need this software or can I also use the Storm/Quickwave programmes to process wave data?

Thank you in advance.

Lisa

Hi Lisa,

1) First off I should say that deploying an AWAC on a subsurface buoy is a fine way to deploy, but you should be aware of the mooring dynamics. More specifically, you should try to get a handle on the natural frequency. Wave directional estimates at this frequency can be corrupted by the mooring response.

Don't worry, estimating this is easier than you think and the method is outlined in a few papers found in our bibliography:
http://www.nortek-as.com/en/knowledge-center/bibliography
See papers: N4000-736 and N4000-722



2) Yes, it is good practice to shoot beyond the surface. The data in the top 10% of the water column is likely suffers from interference, but seeing where the surface lies is often useful in interpreting the data. The warning is there to help manage expectations.

3) You should take the magnetic variation in post processing. It is often good practice to include the magnetic variation or location in the comments permitted during "start deployment". The Quickwave and Storm software allow for you to include this in post processing. 24 degrees... wow!


4) Do not enable "Static mode". AST and all other wave measurement features are automatic and optimized by simply enabling wave measurements.


5) Yes, enable SUV mode.


6) Only enable onboad wave processsing if you (a) have a Prolog with wave proceessing in your AWAC, (b) desire onboard wave processing. Raw data is always recorded, so you will always have what you need for post processing. Onboard wave processing is primarily intended for online applications.

7) Don't bother with ExploreWave software. You have Storm and/or Quickwave, then you are all set.


Good luck,
Torstein