3hr time avarage plot of data

Hello everyone

I am trying to plot .cdf file with a 3hr moving avaerage and i started the code as follwos . I couldnt attach the data as it says data format is not supported. But here is the website to get the data from

"https://swarm-diss.eo.esa.int/#swarm%2FAdvanced%2FPlasma_Data%2F2_Hz_Langmuir_Probe_Extended_Dataset%2FSat_A"

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

data=('SW_EXTD_EFIA_LP_HM_20131216T000000_20131216T235959_0106.cdf');

Ne = cell2mat(cdfread(data,'Variables',{'n'})); % Electron density

ti=(cdfread(data,'Variables',{'Timestamp'})); % Time

%%%%%%%%%%%%%%%%%%%%%% Time conversion to get HH:MM:SS format

for k=1:length(ti)

datenum2(k) = todatenum(ti{k});

end

T = datetime(datenum2, 'Format','HH:mm:ss', 'ConvertFrom','excel');

t1=T';

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

avg_Ne = movmean(Ne, 3*60*60/median(diff(t1)));

plot(t1, avg_Ne);

xlabel('Time');

ylabel('Ne');

title('3-Hour Time Average');

%%%%%%%%% The Error I am having

Error using cdf_3hr_average (line 82)

The denominator in matrix division for duration

arrays must be a real scalar double value.

I would be happy to hear any comments .

Thank you

Answer 1

[Cris LaPierre]

This problem is made much simpler if you leverage the capabilities of cdfread. It can read in cdfepochs as datetimes, simplifiing that step. You can then use movmean to create a 3-hour moving mean (see this example).

% Obtain info about what is in the CDF file
filename = "SW_EXTD_EFIA_LP_HM_20131216T000000_20131216T235959_0106.cdf";
ci = cdfinfo(filename)
ci.Variables

% Load the specified variables
data = cdfread(filename,'Variables',{'n','Timestamp'},"DatetimeType","datetime"); % Electron density, Time
Ne = vertcat(data{:,1}); % Electron density
ti = vertcat(data{:,2}); % Time

% compute a 3 hour moving mean
avg_Ne = movmean(Ne, hours(3), 'SamplePoints', ti)

% Visualize
plot(ti, avg_Ne);
xlabel('Time');
ylabel('Ne');
title('3-Hour Time Average');

Since the data is too large to load here, here is a screenshot of what the final plot looked like for me. I have not gone through the data to verify any of the results.

[Cris LaPierre]

Admitting that I am not familiar with what is appropriate in this field of study, it is my observation that a 3 hour average does not appear to track the raw data very well.

Consider using a shorter window to better represent the raw data. Here is what a 20 minute window looks like.

[root]

Thank you so much for your prompt response.

Your code seems not working for me...here is the error displayed

***********************************************

Error using cdfread>parse_inputs (line 525)

Expected input to match one of these values:

'variables', 'records', 'slices',

'convertepochtodatenum', 'combinerecords'

The input, 'DatetimeType', did not match any of

the valid values.

Error in cdfread (line 132)

options = parse_inputs(filename,varargin{:});

Error in average_3hr (line 9)

data =

cdfread(filename,'Variables',{'n','Timestamp'},"DatetimeType","datetime");

% Electron density, Time

[Cris LaPierre]

What version of MATLAB are you using?

The "DatetimeType","datetime" name-value pair was added in R2022b (see here).

[Cris LaPierre]

If you are using a pre-R2022b version of MATLAB, try using this instead

% pre R2022b (no DatetimeType option)
data = cdfread(filename,'Variables',{'n','Timestamp'},"ConvertEpochToDatenum",true); % Electron density, Time
Ne = vertcat(data{:,1}); % Electron density
ti = datetime(vertcat(data{:,2}),"ConvertFrom","datenum"); % Time

[root]

I am using Matlab_R2020b version.

And now, it worked. Thank you so much!!!