Matlab/ArcGIS processing GPM global monthly precipitation data

GPMPrecipitation data website：https://disc.gsfc.nasa.gov/datasets/GPM_3IMERGM_06/summary?keywords=GPM
The spatial resolution of the precipitation data is0.1°（大约10km）,Global scope includes sea.

1 数据下载

After the access to the site general selectionSubset,Because not need global area precipitation,Can according to their own needs to cut.
But need to register before downloading data,点击网站右上角loginWill lead to the registration screen,进行注册即可.Attention must remember the user name and password,Need to use when subsequent batch download.

注册完成之后,使用subsetThe data date selection、Processing, such as cutting,Note if you select the area cut toUse ‘Refine Region’ for geo-spatial subsetting To check on the data from otherwise equal to didn't cut or global area

2 批量下载数据

I'm here for the south China sea area2001年1月到2021年12Month precipitation data,点击Get Data.
Wait a moment will appear242A file download link,So many can't one by one click to download.点击Download links list,会下载一个txt文本文件,This file contains all the data download link.

这个时候就需要用IDMTo create a task for batch download,如何使用IDM可以自行百度一下.
首先要在IDM选项——The site management add an authorization：站点地址为https://urs.earthdata.nasa.gov,The user name and password is registered website just now that

After adding the authorization,复制txtAll the links in the file,在IDMClick the task,Select add from the clipboard batch download,Automatically identify all of the file download link.

出现error先不用管（If you just add authorized under the condition of no problem）,And then all select、To save the path,Can be downloaded on the points directly determine the.Automatically identify the precipitation data download.

After the download is complete can the next processing.

3 matlabThe data unit conversion

首先得用arcgis读取一个nc文件,然后将其转换为tif格式
arcgis中使用创建NetCDFGrid file tools,Then the data export（以下均使用arcgis pro操作其实都是一样的）

导出tifAlso note that when the dimension of the data size,Behind this to and read onmatlabThe data in the same size or we can't use the geographic coordinate system to save the data.

随后就可以在matlabIn the batch conversion unit,Because what I want is an average annual rainfall of,So the year directly to the12Months for the synthesis of,But ideas are all the same just change a code.

clear all; clc
[ncname,ncpath] = uigetfile('.nc4','请选择ncFile can be multiple','MultiSelect','on');
% ncdisp([ncpath,ncname])
[tifname,tifpath] = uigetfile('.tif','选择tif数据');  % 选择刚才导出的tif文件
[A,GeoRef] = geotiffread([tifpath,tifname]);

k = 1;
for i = 1:numel(ncname)
    scs_pr = ncread([ncpath,ncname{
    i}],'precipitation'); 
    % The geographic distribution of data need to flip up and down is true 
    scs_pr_true = flipud(scs_pr);
    year = str2num(ncname{
    i}(21:24));
    mon = str2num(ncname{
    i}(25:26));
    monthd = [31,28,31,30,31,30,31,31,30,31,30,31];
    if ((mod(year,4)==0 && mod(year,100)~=0) || mod(year,400)==0)
        monthd(2) = 29;  % 判断是否闰年
    end
    mon_days = monthd(mon);
    scs_pr_mon(:,:,mon) = scs_pr_true .* 24 .* mon_days;  % Get the monthly precipitation data,单位mm
    if mod(mon,12) == 0
        scs_pr_year = sum(scs_pr_mon,3);  % And the annual precipitation
        scs_pr_year_k(:,:,k) = scs_pr_year;
        exp = ['geotiffwrite(''SCS_Pr_year_',num2str(year),'.tif'',scs_pr_year,GeoRef)'];
        eval(exp);
        clear scs_pr_mon scs_pr_year;
        k = k+1;
    end
end
scs_pr_year_mean = mean(scs_pr_year_k,3);
geotiffwrite('SCS_Pr_2001to2020_mean.tif',scs_pr_year_mean,GeoRef);  % 得到近20Annual average rainfall

Finally you can get close to20In an average annual rainfall of the south China sea！！！

4 About the accuracy of the data

I try to download the before2021年7月和8Month precipitation data,The scope of and extract the henan province,Calculation about thisGPMHenan province2021年7月和8The months of rain,Found that is more consistent,有些偏高了.