How to write the MATLAB Script for download data?

  1. Access the Product webpage in the PODAAC

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  2. Click Data Access

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  3. DIRECT ACCESS > access HTTPS Link

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  4. You have to “Sign In” and Choose ‘sample day’ for get the longitude, latitude information.

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  5. Click the Opendap and set the option like below

    1. Download Encoding : NetCDF-4
    2. add the Variables : “lat” and “lon”

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  6. Click Get Data

  7. Make new folder for MATLAB Workspace.

    Move the nc file in the new folder

    (You can change the name of nc file)

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  8. Open the new MATLAB script and read the longitude, latitude information of the NC file.

    %% read 'lon', 'lat' data from NC file
clc; clear;

fnm = 'sample_lonlat_20020601_MUR_41.nc4';
ncdisp(fnm)

lon = ncread(fnm, 'lon'); 
lat = ncread(fnm, 'lat');

  9. Find the index of region where you want to download

    Spatial_area = [24, 35, 121, 132];

idlat(1) = findnearpoint(lat, Spatial_area(1));
idlat(2) = findnearpoint(lat, Spatial_area(2));
idlon(1) = findnearpoint(lon, Spatial_area(3));
idlon(2) = findnearpoint(lon, Spatial_area(4));

function id = findnearpoint(base, target)
% find nearest point of "target" from "base"
[~, id] = min(abs(base-target));
end

  10. Prepare the period information with proper format

    period = [2014, 1, 1; 2014, 1, 5];
period2 = datetime(period);
period3 = period2(1):days(1):period2(2);

  11. Back to the website - Add the Variables (time and variables you want) - Copy raw Data Link

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  12. If the url is like this,

    https://opendap.earthdata.nasa.gov/providers/POCLOUD/collections/GHRSST Level 4 MUR Global Foundation Sea Surface Temperature Analysis (v4.1)/granules/20020601090000-JPL-L4_GHRSST-SSTfnd-MUR-GLOB-v02.0-fv04.1.dap.nc4?dap4.ce=/time[0:1:0];/lat[0:1:17998];/lon[0:1:35999];/analysed_sst[0:1:0][0:1:17998][0:1:35999]

    Then, you can split this link into like this

    1. https://opendap.earthdata.nasa.gov/providers/POCLOUD/collections/GHRSST Level 4 MUR Global Foundation Sea Surface Temperature Analysis (v4.1)/granules/
    2. 20020601
    3. 090000-JPL-L4_GHRSST-SSTfnd-MUR-GLOB-v02.0-fv04.1.dap.nc4?dap4.ce=
    4. /time[0:1:0];/lat[0:1:17998];/lon[0:1:35999];/analysed_sst[0:1:0][0:1:17998][0:1:35999]

    Then, you should change the “2” and “4” in the MATLAB.

  13. The example is like this.

    %% load data with URL

% If the downloaded file has the SAME NAME, INCREASE the value of lag_time
lag_time = 3; % seconds between download each files

for loop = 1:length(period3)
    period4 = period3(loop); period5 = datevec(period4); period5 = period5(1:3);
    period6 = sprintf("%d%02.0f%02.0f", period5);

    url1 = "<https://opendap.earthdata.nasa.gov/providers/POCLOUD/collections/>" + ...
        "GHRSST%20Level%204%20MUR%20Global%20Foundation%20Sea%20Surface%20Temperature%20Analysis%20(v4.1)" + ...
        "/granules/";

    url2 = period6;

    url3 = "090000-JPL-L4_GHRSST-SSTfnd-MUR-GLOB-v02.0-fv04.1.dap.nc4?dap4.ce=";

    url4 = sprintf("/time[0:1:0];/lat[%d:1:%d];/lon[%d:1:%d];/analysed_sst[0:1:0][%d:1:%d][%d:1:%d]", ...
        idlat(1)-1, idlat(2)-1, idlon(1)-1, idlon(2)-1, ...
        idlat(1)-1, idlat(2)-1, idlon(1)-1, idlon(2)-1);

    url5 = strcat(url1, url2, url3, url4);
    web(url5)

    pause(lag_time);
end

    Finally, you can automatically download the data!

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