How to convert 15days data into monthly scale?

Question

Aarti Soni 2023-5-25

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https://ww2.mathworks.cn/matlabcentral/answers/1973519-how-to-convert-15days-data-into-monthly-scale

移动：Mathieu NOE 2023-7-19

I have 15days global temperature data for 10years (240 files in .tif format). For every month 2 files are given and I need to take mean of these 15days data to convert into monthly scale (120 files).

Any kind of help would be appreciated.

Thanks

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Mathieu NOE 2023-7-11

ok

can you share a couple of data files and the code your struggling with ?

Aarti Soni 2023-7-19

hi @Mathieu NOE,

https://zenodo.org/record/7441559#.ZEe5AHZBxPY these are the data I am using to create time series. these are the 15days mean data (for 38 years total 912 files), every month is having two files. I just want to take monthly mean of every two data files

Output should be 38year_data = lat X lon X 456

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Answer 1

Mathieu NOE 2023-7-19

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1973519-how-to-convert-15days-data-into-monthly-scale#answer_1275493

移动：Mathieu NOE 2023-7-19

在 MATLAB Online 中打开

hello

I downloaded some files (not all as they are pretty big) to test my code

the image format is grayscale so I get a 2D array (2160x4320) - there is no 3rd dimensions here

the code I suggest so far is pretty simple :

fileDir = pwd; % current directory (or specify which one is the working directory)
S = dir(fullfile(fileDir,'PKU*.tif')); % get list of data files in directory
%% step 1 : get years and month data from file names 
for k = 1:numel(S)
    file = S(k).name; %
    % get year / month data 
    i1 = findstr(file,'_');
    i2 = findstr(file,'.tif'); % or tif
    tmp = file(i1(end)+1:i2-1);
    file_year(k) = str2num(tmp(1:4));
    file_month(k) = str2num(tmp(5:6));
    filename{k} = file;
    
end
%% step 2 : process the data  
[file_year_unic,ia,ic] = unique(file_year);
for k = 1:numel(file_year_unic) % loop over years
    y = file_year_unic(k);
    for m = 1:12  % loop over 12 months
        id = find(file_year==y & file_month == m); % find which file names to pick 
        % load data files
        nid = numel(id);
        if nid == 1 % we have only one file 
            out = imread( fullfile(fileDir, filename{id})); %
        elseif nid == 2 % we have two files per month
            out1 = imread( fullfile(fileDir, filename{id(1)})); %
            out2 = imread( fullfile(fileDir, filename{id(2)})); %
            out = (out1+out2)/2; % mean values (NB : NaN + numeric = NaN output)
        end
        % store the results only if nid > 0
        if nid>0
            filename_out = ['averaged_' sprintf('%04d', y) sprintf('%02d', m) '.tif'];
            imwrite(out,fullfile(fileDir,filename_out));
        end
    end
end
    