MATLAB | GLASS Global Vegetation Photosynthetically Active Radiation Absorption Ratio FAPAR Data from 1982 to 2018

1. Data Link

https://www.glass.hku.hk/download.html

2. Batch Download Specified Year Data Using MATLAB

base_url = 'https://www.glass.hku.hk/archive/FAPAR/AVHRR/0.05D/';
download_dir = 'D:\GLASS\FAPAR';
if ~exist(download_dir, 'dir')
    mkdir(download_dir);
end
start_year = 1985;
end_year = 1987;
year_links = {};
html = webread(base_url);
expr = '<a href="(\d+)/">';
tokens = regexp(html, expr, 'tokens');
for i = 1:length(tokens)
    y = str2double(tokens{i}{1});
    if y >= start_year && y <= end_year
        year_links{end+1} = [base_url tokens{i}{1} '/'];
    end
end
for y = 1:length(year_links)
    year_url = year_links{y};
    year_name = regexp(year_url, '/(\d+)/$', 'tokens');
    year_name = year_name{1}{1};
    year_dir = fullfile(download_dir, year_name);
    if ~exist(year_dir, 'dir')
        mkdir(year_dir);
    end
    try
        html_year = webread(year_url);
    catch
        continue;
    end
    hdf_expr = '<a href="([^"]+\.hdf)">';
    hdf_tokens = regexp(html_year, hdf_expr, 'tokens');
    for h = 1:length(hdf_tokens)
        hdf_name = hdf_tokens{h}{1};
        hdf_url = [year_url hdf_name];
        save_path = fullfile(year_dir, hdf_name);
        if exist(save_path, 'file')
            continue;
        end
        options = weboptions('Timeout', 60);
        try
            data = webread(hdf_url, options);
            fid = fopen(save_path, 'w');
            fwrite(fid, data);
            fclose(fid);
        catch
            pause(5);
        end
    end
end

3. Viewing HDF Attributes with Panoply4. Convert HDF to TIFF Using MATLAB

input_folder = 'D:\GLASS\FAPAR';
output_folder = 'D:\GLASS\FAPAR_TIF';
years = dir(fullfile(input_folder, '*'));
years = years([years.isdir] & ~startsWith({years.name}, '.'));
for y = 1:length(years)
    year_folder = fullfile(input_folder, years(y).name);
    out_year_folder = fullfile(output_folder, years(y).name);
    if ~exist(out_year_folder, 'dir')
        mkdir(out_year_folder);
    end
    hdf_files = dir(fullfile(year_folder, '*.hdf'));
    for f = 1:length(hdf_files)
        hdf_path = fullfile(year_folder, hdf_files(f).name);
        info = hdfinfo(hdf_path);
        fapar_data = [];
        for v = 1:length(info.Vgroup)
            if strcmp(info.Vgroup(v).Name, 'GLASS09B02')
                data_fields = info.Vgroup(v).Vgroup(1);
                for d = 1:length(data_fields.SDS)
                    if strcmp(data_fields.SDS(d).Name, 'FAPAR')
                        fapar_data = hdfread(hdf_path, data_fields.SDS(d).Name);
                    end
                end
            end
        end
        if isempty(fapar_data)
            continue;
        end
        fapar_data = double(fapar_data) * 0.004;
        fapar_data(fapar_data < 0 | fapar_data > 1) = NaN;
        fapar_data = flipud(fapar_data);
        R = georefcells([-90 90], [-180 180], size(fapar_data));
        [~, name, ~] = fileparts(hdf_files(f).name);
        tif_path = fullfile(out_year_folder, [name, '_FAPAR.tif']);
        geotiffwrite(tif_path, fapar_data, R);
    end
end