Velocity fields in .wad file (ADCP)

Hi

I am trying to find out what the Velocity fields (10, 11, 12) in the ADCP wad file are.  Persumably they are the velocities used for PUV calculation of wave parameters in STORM.

At setup I nominated XYZ mode, so I presume the fields contain XYZ (as opposed to ENU or Beam data).  However, which bin are these data from?

Thanks

Kevin

W3101G01.wad
1   Month                            (1-12)
2   Day                              (1-31)
3   Year
4   Hour                             (0-23)
5   Minute                           (0-59)
6   Second                           (0-59)
7   Pressure                         (dbar)
8   Spare
9   Analog input
10   Velocity (Beam1|X|East)          (m/s)
11   Velocity (Beam2|Y|North)         (m/s)
12   Velocity (Beam3|Z|Up)            (m/s)
13   Velocity (Beam4)                 (m/s)
14   Amplitude (Beam1)                (counts)
15   Amplitude (Beam2)                (counts)
16   Amplitude (Beam3)                (counts)
17   Amplitude (Beam4)                (counts)

Hi Kevin,

The coordinate system (ENU, XYZ, BEAM) depends on which instrument you use.

If you are using the Aquadopp current meter, then the coordinate system is that which you choose at configuration time.

If you are using the Aquadopp Profiler then the coordinate system is always in BEAM coordinates for the wave burst measurement. The coordinate system you specify in the deployment planning applies to the current profiles only.

The location of the measurement cells is fairly close to the instrument during the wave measurement.  For the Aquadopp Current meter it is the blanking specified in the configuration.  The default is 0.35 meters.  

The Aquadopp Profiler comes in a variety of transmit frequencies, and this means that the default blanking will be slightly varied as well:
2 MHz     0.2 m
1 MHz     0.4 m
600 kHz   0.5 m
400 kHz   1.0 m

Hope this helps,
Torstein

Thanks for that response Torstein.  I am using a 2MHz Profiler with blanking distance of 10cm.  I THINK you are saying that the beam velocities recorded are the first bin above the blanking distance.  Is that right? I recall that I have seen a method for turnign beam velociies into XYZ posted here, but I can't find it.  Could you please remind me of how that is done.  Thank you.

Kevin

Hello Kevin,
Yes you are correct that the velocities are located in the first bin above the blanking distance.  In fact this is the only bin collected during the wave burst mode.

If you are handy with MatLab, then I encourage you to jump to this forum entry below and download the script.  The conversion between coordinate systems involves using the instruments beam orientation and the attitude (heading, tilt) of the instrument to perform the conversion.  The "Transformation matrix" is found in the header file (*.HDR) and the attitude information is found in the wave header file (*.WHD).

Forum entry for coordinate conversion of AWAC velocities

good luck,
Torstein

Hi again

I have just been playing withe these data.

A couple of questions:

I understand from the above that the beam data recorded in the whd file is for the first cell above the blanking distance for the instrument I am using (0.1m).  However, is this the first cell as detailed in the Current profile box of the STANDARD menu (in my case set at 0.2m), or the first cell as detailed in the Wave bursts box on the ADVANCED menu (in my case set at 0.5m).

Secondly, I have been using the Transformation matrix from the .hdr file as suggested.  It happens to be exactly the same as the Matlab script that you pointed me to, even though my unit is a 2MHz, horizontal ADCP, not an AWAC. I had exected to have to change it. Are teh transformation matrices the same for many systems.

Thank you.

Kevin

Hi Kevin

Quote

I understand from the above that the beam data recorded in the whd file is for the first cell above the blanking distance for the instrument I am using (0.1m).  However, is this the first cell as detailed in the Current profile box of the STANDARD menu (in my case set at 0.2m), or the first cell as detailed in the Wave bursts box on the ADVANCED menu (in my case set at 0.5m).

For the wave data (which is what the .wad file contains, the blanking is picked from the advanced menu and the cell size is taken from the wave burst section.

Quote

Secondly, I have been using the Transformation matrix from the .hdr file as suggested.  It happens to be exactly the same as the Matlab script that you pointed me to, even though my unit is a 2MHz, horizontal ADCP, not an AWAC. I had exected to have to change it. Are the transformation matrices the same for many systems.

All systems that have three beams pointing 120 degrees apart and 25 degrees relative to the vertical have the same transformation from beam to XYZ coordinates.  If any of the two angles change, the matrix will change.

Best regards, Atle Lohrmann

Hi Kevin,

As I got slightly confused myself when reading this thread I will try to clarify how the data are collected, stored and converted when you do wave measurements with an Aquadopp Profiler.

1. The Aquadopp Profiler always collects wave data in beam coordinates.
2. The Aquadopp Profiler always stores binary wave data in beam coordinates. So the .prf files will contain beam data for the wave measurements.
3. But when you come to the converted ASCII-files the format changes. When you convert the .prf-file with the AquaPro software the beam data are converted to the coordinate system that you have specified in the configuration. This is indicated in the format description that you listed (Beam1|X|East).

So since you specified XYZ in the setup the converted ASCII data in the .wad file will also be in XYZ.

Best regards,
Sven Nylund