热带降雨测量卫星（Tropic Rainfall Measurement Mission,TRMM）是美国宇航局（NASA）和日本宇航探索局（JAXA）曾在1997年时联手发射在全球的热带上空的一种遥感卫星，主要是用来观测降水的，其最开始的观测区域是南纬38°北纬38°、西经180°东经180°，在2001年8月时TRMM卫星进行了一次变轨，因此它的观测范围扩展到了南纬50°~北纬50°，它的观测范围显然扩大了。下载的TRMM数据格式为.nc，往往需要转换为.tif格式，这里详细介绍一下IDL批量转为tif格式。
打开IDL软件，在IDL软件下通过编写代码实现TRMM数据.nc格式批量转换为tif 格式，转换前得先准备好存放文件夹。转换的代码如下所示：
pro batch ;
reftif = read_tiff('E:\2018\GIS Spacial anlayse\GISkeshe\Point\precipitation_Layer1.tif',geotiff=geo);
filelist = file_search('F:\TRMM\trmm','*.nc');
for i=0,n_elements(filelist)-1 do begin
name = strsplit(file_basename(filelist[i]),'_',/Extract);3B43.20120101.7.HDF.nc
tifname = name[0] + '_' + name[0]
data_SMOS = ncdf_readv(filelist[i],varname = 'precipitation')
index = where(data_SMOS ge 1e+020) & data_SMOS[index]=0
data_AOT = ncdf_readv(filelist[i],varname = 'precipitation')
index = where(data_AOT ge 1e+020) & data_AOT[index]=0
;data_SH = ncdf_readv(filelist[i],varname = 'Qair_GDS0_SFC')
;index = where(data_SH ge 1e+020) & data_SH[index]=0
dim = size(data_SMOS)
data_SMOS2 = fltarr(dim[1],dim[2])
data_AOT2 = fltarr(dim[1],dim[2])
data_SMOS3 = fltarr(dim[2],dim[1])
data_AOT3 = fltarr(dim[2],dim[1])
;data_SH2 = fltarr(dim[1],dim[2])
for m = 0,dim[1]-1 do begin
for n = 0,dim[2]-1 do begin
data_SMOS2[m,n] = data_SMOS[m,abs(n-dim[2]+1)]
data_AOT2[m,n] = data_AOT[m,abs(n-dim[2]+1)]
;data_SH2[m,n] = data_SH[m,abs(n-dim[2]+1)]
endfor
endfor
for n = 0,dim[2]-1 do begin
for m = 0,dim[1]-1 do begin
data_SMOS3[n,m] = data_SMOS2[m,n]
data_AOT3[n,m] = data_AOT2[m,n]
;data_SH2[m,n] = data_SH[m,abs(n-dim[2]+1)]
endfor
endfor
for n = 0,dim[2]-1 do begin
for m = 0,dim[1]-1 do begin
data_SMOS3[n,m] = data_SMOS2[m,dim[2]-1-n]
data_AOT3[n,m] = data_AOT2[m,dim[2]-1-n]
;data_SH2[m,n] = data_SH[m,abs(n-dim[2]+1)]
endfor
endfor ;
write_tiff,'E:\2018\GIS Spacial anlayse\GISkeshe\Point'+tifname+'.tif',data_AOT3,geotiff=geo,/FLOAT
endfor
end;
function ncdf_readv, ncdf_file, varname = varname
if (n_params() ne 1) then $
message, 'USAGE: result = ncdf_readv(ncdf_file, varname=varname)';
if (keyword_set(varname) eq 0) then begin
print, 'Keyword VARNAME not supplied, returning array of variable names'
cdfid = ncdf_open(ncdf_file)
namearr = ncdf_vardir(cdfid)
ncdf_close, cdfid
return, namearr
endif
; Get data
cdfid = ncdf_open(ncdf_file)
;varid = ncdf_varid(cdfid,GRIB_name)
varid = ncdf_varid(cdfid,varname)
ncdf_varget,cdfid,varid,data
; Close netCDF files
ncdf_close, cdfid
return, data
end
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