high resolution profiling with Aquadopp Profiler

We are using a transect of 3 Aqd Profilers across a shallow reef (1 deep).  For the purpose of looking at infragravity waves, we would like to change our sampling scheme to obtain 1 Hz profiles continuously for up to 4 hrs.  This is a remote deployment, so the instruments are running on 5x165 Wh lithiums with the 161 MB upgrade.  Obviously, this is a demanding scheme (mem & batt), so our initial hope was to burst sample, i.e. 1 Hz for 4 hours X times per day or such.

Currently I can see no way of setting the Profiler's sampling scheme to obtain such bursts.  The "wave" mode is similar, but unfortunately its duration is limited to 2048 s.

I'm confident we could achieve this using a PC interface and logging to the PC, but the experiment site precludes this.

Help !

Hi Tyson,

I have to check whether there are some possibilities in the software to upload an appropriate deployment file. In case we have to generate the deployment file for you, it would be helpful if you could provide me with some more details on the deployment site, such as:

- Minimum distance between surface and the transducer head throughout the deployment?
- Duration of the deployment?
- Number of preferred 4 hour bursts per day?

I assume these are 2MHz systems?

Best regards,
Sven Nylund

Sven,

For the 3 shallow sensors, they "go dry" at negative tidal heights.  This would be for 3 hr periods multiple times per month.  The rest of the time they're at ~ 0.5-1.0 m depth.

The 1 deep sensor has a minimum separation of 4.981 m.

Our previous deployment durations have been 3 months.  We would be willing to do 2 months maybe.

The number of 4 hour bursts per day.  Let's hope for 2.

Yes, 2 MHz systems.

Time resolution aside, I'm trying to conceptualize how to optimize the cells for the shallow sensors.  Too few cells would mean a significant number of them hitting the surface.  Too many cells stresses our battery and memory limits, but yields more useful data.  I haven't looked into the measurement precisions for our 0.10 m cells vs larger cells.  I'm assuming my main concern for changing cell size is not velocity precision, rather contamination from surface reflectance.

Many thanks for looking into this,
Tyson

by the way, this might help:
images from deployment
PILOT Experiment

I just checked the photos.  Need anybody to come along?  " />'>

- Atle Lohrmann

Hi Tyson,

It seems to me that a modified wave burst sampling scheme would be the best choice for the shallow water sensors. You would only get one velocity cell, but because of the reduced storage requirement you would be able to sample more bursts.

This would require that we send you a new software version. What I have in mind is to allow for arbitrary number of wave samples (in practise up to 30000 samples or so) and to allow smaller wave cell sizes than the current limitation of 1m. The blanking would be fixed at 20cm which I think is a fair number for the shallow water sensors.

Does this sound like a setup you could use?

For the deep water sensor maybe you could use a large velocity cell size to get good data even with the relatively small blanking distance. The power consumption will probably limit how large cell size you can use.

What do you think?

Regards,
Sven

Atle - extra hands are always appreciated  " />'>   Be warned though, a day in Guam is like a day in the sauna.

Sven,

The modified wave burst scheme sounds quite feasible.  For the shallow sensors, a 20 cm blanking distance combined with ~ 40 cm cell size would fit nicely.  

Out of technical curiousity, why is 20 cm a good blanking distance?  Long enough to let the transducer settle, but why would the blanking distance ever change?

The deep sensor also sounds appropriate.  Hopefully I can achieve a cell size ~ 1-2 m, given our batteries.

So the answer is yes, please.

Hi Tyson,

A new version of the software is on its way  " />'>

As for blanking distance, 20 cm is long enough to let the transducer settle as you say. It is also a reasonable value for avoiding flow interference from the instrument.

Best regards,
Sven