How to convert 15days data into monthly scale?

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

[Mathieu NOE]

hi

you need to load files two by two and average the result, then save the result in a new file (120 total)

where do you have trouble ?

[Aarti Soni]

@Mathieu NOE thanks for the answer.

I resolved the problem.

[Aarti Soni]

@Mathieu NOE

Problem is not completely solved, I am stuck in reshape the 3d data (180 X 360 X 240).

The reshape function is working for 2d timeseries but how can I use this function for 3d data for averaging of every two files to make it monthly mean (180 X 360 X 120) or is there any other way to solve this?

Thanks.

[Mathieu NOE]

ok

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

[Aarti Soni]

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

Answer 1

[Mathieu NOE]

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