Possible 95% Threshold Discrepancy

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Everett.Perry
Posts: 33
Joined: Tue Jan 29, 2013 9:53 am
Organization: Texas Tech University
Location: Oregon

Possible 95% Threshold Discrepancy

Postby Everett.Perry » Mon May 13, 2013 3:36 pm

Two data thresholds are used for the M4 tower sonic data processing (92% and 95%):

Code: Select all

tower.sonicpassrate = 0.920000000000000
tower.sonicrotaterate = 0.950000000000000


I would have expected any values that use the sonic (u, v, w) coordinate system (i.e. rotated coordinate system) to have at least 95% of the data record. This does not seem to be the case. Instead it seems that the 92% threshold is used rather than the 95% threshold for the rotated data.

I have included a small script that will identify the issue. I have also posted the figure from the script output. In order to run the script, load the file into MatLab from the server located here:

http://wind.nrel.gov/MetData/135mData/M ... 13_May.mat

And then run the program (or just look at the attachment).

Notice in the image that the nPoints percentage is at 92% before any plot points are visible. When nPoints are less than 92%, all MO length values are NaN. The NaN’s are of course expected except that they should occur below 95%, NOT below 92%. Am I thinking about these two thresholds correctly? I have probably just missed something, but any help would be appreciated.

Everett

Code: Select all

%load('2013_May.mat') This is the current M4, 10-minute data file on the server

x = all_data.MO_Length_Sonic_15m.npoints/12000; % percentage of data points available (row vector)
y = all_data.MO_Length_Sonic_15m.val; %Values of Monin Obukhov Lengths (row vector)

temp = [x ; y]'; %create matrix with 2 columns
test = sortrows(temp); %Sort rows according to percentage of data points available (i.e. the x variable above)

figure
plot(test( :,1), test( :,2)/ min(test(: ,2))) %Normalized by minimum MO Length
xlabel('nPoints (Normalized by 12000) (i.e. %)');
ylabel('Monin Obukhov Length (Normalized by Min Value)');
title('Sonic 15m MO Length Vs. nPoints');
Attachments
Sonic 15m MO Length Vs nPoints.png
Image: MO Length Vs. Percentage of Data
Sonic 15m MO Length Vs nPoints.png (4.65 KiB) Viewed 7616 times
Everett Perry
PhD Candidate, National Wind Institute
Texas Tech University

Andy.Clifton
Posts: 83
Joined: Wed Feb 29, 2012 3:13 pm
Organization: NREL
Location: Boulder, CO
Contact:

Re: Possible 95% Threshold Discrepancy

Postby Andy.Clifton » Mon May 13, 2013 4:29 pm

That's another bug, apparently. It seems that the wrong threshold was being used in the code, so that intervals with 92% or more data were being rotated. I will try to post updated data in the next few weeks.
Andy Clifton, Ph.D.
Senior Engineer

Andy.Clifton
Posts: 83
Joined: Wed Feb 29, 2012 3:13 pm
Organization: NREL
Location: Boulder, CO
Contact:

Re: Possible 95% Threshold Discrepancy

Postby Andy.Clifton » Thu May 16, 2013 5:04 pm

I've just started the new code running (version 1.27) which should correct this. I'll post a link to that update in a minute.

I really like the comparison of the range of MO-length with the data availability. I had a feeling that it was important but I'd not managed to show it quite as well as the plot that is shown in the previous message. Thanks!
Andy Clifton, Ph.D.
Senior Engineer


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