Talk:Processing your ADCP data using structure function techniques: Difference between revisions

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[[User:Djwain|Djwain]] ([[User talk:Djwain|talk]]) 22:51, 14 November 2021 (CET)I agree with Justine on the three ways of dealing with the data being somewhat confusing.- I am having a very hard time visualizing what is being explained in item 1 because I don't process my data this way. I think we probably need to be giving some guidance on why you might do a forward vs a center difference and maybe branch based on that. The forward difference example is really nice and helpful I think!
[[User:Djwain|Djwain]] ([[User talk:Djwain|talk]]) 22:51, 14 November 2021 (CET)I agree with Justine on the three ways of dealing with the data being somewhat confusing.- I am having a very hard time visualizing what is being explained in item 1 because I don't process my data this way. I think we probably need to be giving some guidance on why you might do a forward vs a center difference and maybe branch based on that. The forward difference example is really nice and helpful I think!
:[[User:Yuengdjern|Yuengdjern]] ([[User talk:Yuengdjern|talk]]) 16:42, 15 November 2021 (CET) Right this seems to where the potential for contention arises,  given the conversation here and also on Teams.  So I think for now we pick the most common and add an aside that there are alternatives. Dumping text here so it is saved:
:[[User:Yuengdjern|Yuengdjern]] ([[User talk:Yuengdjern|talk]]) 16:42, 15 November 2021 (CET) Right this seems to where the potential for contention arises,  given the conversation here and also on Teams.  So I think for now we pick the most common and add an aside that there are alternatives. I've also moved this stuff to a new page to keep the step-by-step instruction page flowing.
 
# If  <math>D_{ll}(n,\delta)</math> was evaluated using a forward-difference scheme, the regression is done for the combined data from all bins in the selected range, hence the maximum number of <math>D_{ll}(n, \delta)</math> values for each separation distance will be the number of bins in the range less 1 for <math>\delta</math> = 1, reducing by 1 for each increment in <math>\delta</math>, with the regression ultimately yielding a single  <math>\varepsilon</math> value for the data segment
# If <math>D_{ll}(n,\delta)</math> was evaluated using a bin-centred difference scheme, the regression can either be done:
#* for each bin individually, with a single <math>D(n, \delta)</math> for each separation distance, ultimately yielding an <math>\varepsilon</math> for each bin; or
#* by combining the data for all of the bins, with each separation distance having a <math>D_{ll}(n, \delta)</math> value for each bin, with the regression again ultimately yielding a single <math>\varepsilon</math> value for the data segment.
# The regression is typically done as a least-squares fit, either as: <br /><br /> <math>D_{ll} = a_0 + a_1 (\delta r_0)^{2/3}</math>; or as <br /> <math>D_{ll} = a_0 + a_1 (\delta r_0)^{2/3}+a_3((\delta r_0)^{2/3})^3 </math> <br /><br /> the former being the [[canonical structure function method | canonical method]] that excludes non-turbulent velocity differences between bins, whereas the latter is a [[modified structure function method | modified method]] that includes non-turbulent velocity differences between bins due to any oscillatory signal (e.g. surface waves, motion of the ADCP on a mooring).
 


[[User:Djwain|Djwain]] ([[User talk:Djwain|talk]]) 22:53, 14 November 2021 (CET)I also agree that step 7 should probably be in QA2
[[User:Djwain|Djwain]] ([[User talk:Djwain|talk]]) 22:53, 14 November 2021 (CET)I also agree that step 7 should probably be in QA2

Revision as of 16:30, 15 November 2021

Jmmcmillan (talk) 21:50, 12 November 2021 (CET) Can we change the title of this page to be more specific? Like "Computing the structure functions and dissipation rates"

Yuengdjern (talk) 16:42, 15 November 2021 (CET) It's pretty hard to change page names without actually just creating new ones. we can 'move' pages and then there'll be a redirect shown at the top of the page, because 'move' pretty much creates a new page. Will play around with that.

Jmmcmillan (talk) 21:54, 12 November 2021 (CET) I find the use of [math]\displaystyle{ D(n,\delta) }[/math] a little confusing. In reality, for each range bin and each time ensemble, D only depends on [math]\displaystyle{ \delta }[/math]. Can we drop the n for simplicity?

Djwain (talk) 22:44, 14 November 2021 (CET)I agree here - we don't actually define n on this page, so it is confusing to have it in the definition of v' and D. I think I wrote this originally and was basing it on the way my code is written, but really mean something like D_n(delta) where n denotes which bin we are differencing around or from.
Djwain (talk) 22:44, 14 November 2021 (CET)Having just looked through the differencing examples which use the D(n,delta) nomenclature and are quite clear I think, we probably need to stick with this (otherwise we have to change a bunch of other pages).

Djwain (talk) 22:51, 14 November 2021 (CET)I agree with Justine on the three ways of dealing with the data being somewhat confusing.- I am having a very hard time visualizing what is being explained in item 1 because I don't process my data this way. I think we probably need to be giving some guidance on why you might do a forward vs a center difference and maybe branch based on that. The forward difference example is really nice and helpful I think!

Yuengdjern (talk) 16:42, 15 November 2021 (CET) Right this seems to where the potential for contention arises, given the conversation here and also on Teams. So I think for now we pick the most common and add an aside that there are alternatives. I've also moved this stuff to a new page to keep the step-by-step instruction page flowing.

Djwain (talk) 22:53, 14 November 2021 (CET)I also agree that step 7 should probably be in QA2

Yuengdjern (talk) 16:31, 15 November 2021 (CET) moved Step 7 to top of QA2

Djwain (talk) 22:53, 14 November 2021 (CET)A schematic is definitely needed here - SF is much easier to visualize I think than read! I don't have any schematics that I have made (and thus own for distribution).


Yuengdjern (talk) 16:42, 15 November 2021 (CET) JMM's comment about referring to QA2. I think I second that. Dumping the cut text here in case we want it later, but adding a link to QA2. Pasted text:

Some things to consider are: [JMM: SHOULD WE INCLUDE THESE HERE, OR MAKE A LINK TO A PAGE ABOUT QUALITY CONTROL METRICS TO COMPUTE?]

    • Including [math]\displaystyle{ D(n,\delta) }[/math] for [math]\displaystyle{ \delta=1 }[/math] may be inappropriate since the velocity estimates from adjacent bins are not wholly independent, therefore the impact of its inclusion should be evaluated
    • Keep a record of the number of instances when the squared velocity difference is evaluated for each bin [math]\displaystyle{ n }[/math] and separation distance [math]\displaystyle{ \delta r_{0} }[/math] and their distribution because they are potential quality control metrics
    • The impact of additional quality criteria can also be tested e.g. valid data requirements for all intermediate separation distances, so for a forward-difference scheme with [math]\displaystyle{ n=2 }[/math] and [math]\displaystyle{ \delta=5 }[/math], require all data in bins 2 to 7 to meet Level 1 QC requirements for the profile to be included when averaging to calculate [math]\displaystyle{ D(n,\delta) }[/math]

Yuengdjern (talk) 16:55, 15 November 2021 (CET) making a global change to the wiki page to change D to DLL because that's what our netcdf variable is.

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