upper lawer
Hello,
I made a test with my new eco ADCP.
We were in 5.2 m depth with a 0.5 deg of tilt and in a river flat.
The upper layer that the webapp give me is 3.1 m.
The upper I can put is 2.5 m.
Is it normal that we cannot see datas closer tothe surface?
I saw in the FAQ that with 20m depth The upper Layer can be 5m(25%). For me it's 50%.
Thank you very much
Tanguy
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Official comment
Hello Tanguy
Thanks for reaching out to us with this question. Although it’s rare, yes, there can be situations where a region larger than normal near the surface is discarded by the Eco’s automatic data quality control. While it’s not immediately clear from your very short deployment (less than 30 minutes long), below are two key factors that impact how much near-surface data gets rejected.
First, water depth. In order to work from 30 cm up to 20 m without user intervention, the Eco automatically adjusts the length of the pulses is sends based on an estimate of the water level. This is done in steps, and so at times you may be right on the starting or trailing edge of one of these step changes, which influence the thickness (spatial resolution) of each depth layer available.
Second, atmospheric pressure. The Eco uses the standard atmospheric pressure (101,325 Pa) as an offset for its absolute pressure sensor, which is then used in combination with the acoustic altimeter to determine water depth. In almost all instances, this value is more than adequate. Sometimes, however, it may lead to a change that, combined with other factors, could result in a deviation—up or down—from the true water depth. A way that may improve this is to start the Eco in air prior to deployment. This is a similar process to deploying it at a high elevation (e.g., see the “Is it ok to deploy an Eco in a high elevation mountain stream or lake?” FAQ in the Eco App).
Finally, keep in mind that the Eco is a self-configuring ADCP, which means that we have to take a conservative approach to data screening to guarantee that all data delivered is of the highest quality.
Hope this addresses your question, but please feel free to reach out if you need further assistance.
Comment actions -
Hello David,
We have made 1 week of records.
the problem steel the same. We don't have data above 2m of the surface.
the maximum depth is 5.7m and eco automatically adjust the lawers at 5.29m, 4.83m and 4.36m.
we don't have problème with atmospheric pressure because here in French Giaina it is very stable around 1012 HPa.
For us it is a problem because in an estuary we have big gradient near between the surface and the bottom. And we cannot see it here
Maybe your quality filter is to strong for us.
Is it possible to have the raw datas?
thank you very much
Tanguy
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Hello Tanguy
If your interest is to get data as close to the surface as possible, then I would recommend extending the Eco's mooring line another 1-2 m. This will allow the Eco to use shorter pulses and therefore get you closer to the surface (see below FAQ).
By the way, this seems like an interesting site! Good mix of tidal flow and conditions (see below). Exciting work you are doing :-)
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Hello David,
You are sure that is our Data because I have this when I put 2 m for upper lawer:If we had what you show I will be very happy
we cannot put a longer rop because we need all the water column. as you can see in the picture we are in an esturary, so we have some big stratification and sometimes an current inversion in the column.
Are you sure that in the future it will be impossible to have the raw datas with indice of quality?
I know that it's not possible to have the same results with a 5000 euros ADCP. We just want to know how far we can go with it.
In any case we are very happy to have a very simple and cheap ADCP with a great release.
Thank you very much for your anwsers.
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Hi Tanguy
Yes, that is definitely your data set :-) You are indeed capturing the transition zone during high tide. But, keep in mind that the Eco App does not adjust the depth layer positions based on changes in water level. So if the tide drops, then you may miss the Upper Layer if the water level drops too much. We are considering adding this functionality in a future release, but for now, see the below FAQ. Not too much of a compromise for a 5000 EUR ADCP as you said ;-)
However, the data are there, and you just need to adjust the positions of the layers if you'd like to see them. For example, see the two images below.
By the way, as the Eco is for up-looking operation only, I generally find it easier to use the "Above Eco" option when adjusting the layers' positions (rather than the "Below Surface" option). The above images came from the following depth choices as "Above Eco": 3.8, 2.6, and 1.0 m for the top image, and 1.9, 1.0, 0.5 m for the bottom image.
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Hello David,
I'am really sorry to bother you, I just want to understand how it's works and after you will never eard about me...;)
I didn't know that you see my datas in your local time, that's why I thought it was not mine.
I have a question and maybe I will understand better. when I take 3 m for the upper lawer. 3 m is the top or the bottom of the lawer?
if it's the top why we don't have datas under 2m above the surface. I said surface and not depth max, it means that for a layer at 3m depth above the max we can't see under 4.4 m depth. we haven't waves so 1 m aboce the surface normaly the datas should be good.
Your ADCP is great but I'm used to configure and filter the datas on my own. I understand why you that, it's very easy and the datas are directly good.
we have put 3 of your ADCPs in 3 part of a estuary. I Think the datas will be great
Thnak you very much for your time.
Tanguy
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Hi Tanguy
No need to apologize. You are not bothering :-) We're happy to help out our customers and glad to see you making good use of the Eco!
For any given depth layer, the value given is neither the top nor the bottom of the layer, but at that specific depth. The Eco detects velocity at multiple depth intervals throughout the profile, just like a standard ADCP. It then selects three of these depth intervals, based on user-defined Depth Layer position, and returns the speed and direction at these three depths.
Hope this makes it clearer.
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