Technology Lesson

Reading ERS ASAR Data and Creating Quicklooks

In this previous post it was described how gdal reads Radarsat SAR data. I want to read ERS /ASAR data and create quicklooks for each file.

ERS /ASAR data has different formats, files ending with *.001 , *.E1, *.E2 or *. N1  Gdal can read all these formats, also the *.001 files which not all software reads. For the latter, the "DAT_01.001" is the file to be passed to gdal.

As first step, I create a list containing all files with these endings. I use os.walk to recursively search through all folders:

filelist_CEOS = []
for root, dirnames, filenames in os.walk(Z:\ERS_Envisat_SAR\Arctic\2005):
  for filename in fnmatch.filter(filenames, DAT_01.001):
      filelist_CEOS.append(os.path.join(root, filename))

filelist_E1E2 = []
for root, dirnames, filenames in os.walk(Z:\ERS_Envisat_SAR\Arctic\2005):
  for filename in fnmatch.filter(filenames, *.E1):
      filelist_E1E2.append(os.path.join(root, filename))      
for root, dirnames, filenames in os.walk(Z:\ERS_Envisat_SAR\Arctic\2005):
  for filename in fnmatch.filter(filenames, *.E2):
      filelist_E1E2.append(os.path.join(root, filename))  
for root, dirnames, filenames in os.walk(Z:\ERS_Envisat_SAR\Arctic\2005):
  for filename in fnmatch.filter(filenames, *.N1):
      filelist_E1E2.append(os.path.join(root, filename)) 

gdalwarp is able to read all of this formats and I can proceed to process all the files from this filelist, calling gdalwarp from within a Python script. This map-projects the raw SAR file and creates a GeoTIFF:

os.system(gdalwarp -tps  -t_srs EPSG:32633  + file_from_filelist +   + outputfilename )  

For a small quicklook a convert it to jpeg and make it smaller:

os.system(gdal_translate -of JPEG -ot byte -outsize 20% 20% -scale 0 1000 0 255  + outputfilename +   + browseimage )

The whole script reading in all ERS /ASAR images and creating a quicklook can be found here and is hopefully documented well enough.