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processing scenes over ocean without a DEM

See original GitHub issue

I have a set of Level 1 GRD data taken from Copernicus which I wanted to geocode and calibrate using pyroSAR.

OS: Ubuntu 18.04

Environment Used: Anaconda environment

Library versions: pyroSAR: version 0.11.1 from conda-forge SNAP: 8.0

Files:

S1A_EW_GRDH_1SSH_20200317T225506_20200317T225606_031721_03A873_CB43.zip
S1A_EW_GRDM_1SSH_20191215T231834_20191215T231938_030365_037956_C2B6.zip
S1B_EW_GRDH_1SDH_20190820T075249_20190820T075349_017666_0213C3_F0A9.zip

Code:

from pathlib import Path
from pyroSAR.snap import geocode 

sar_zips = [str(Path.cwd() / i) for i in Path("./data").iterdir() if i.suffix == ".zip"]
outdir = "./outdir"

out_proj = 4326

geocode(
    infile=sar_zips[0],
    outdir=outdir,
    t_srs=out_proj,
    scaling="linear",
    speckleFilter="Refined Lee",
)

However the process produced a (seemingly) blank TIF.

Output of gdalinfo S1A__EW___A_20200317T225506_HH_NR_Orb_TF_Spk_TC.tif

Driver: GTiff/GeoTIFF
Files: S1A__EW___A_20200317T225506_HH_NR_Orb_TF_Spk_TC.tif
       S1A__EW___A_20200317T225506_HH_NR_Orb_TF_Spk_TC.tif.aux.xml
Size is 58554, 27919
Coordinate System is:
GEOGCRS["WGS 84",
    DATUM["World Geodetic System 1984",
        ELLIPSOID["WGS 84",6378137,298.257223563,
            LENGTHUNIT["metre",1]]],
    PRIMEM["Greenwich",0,
        ANGLEUNIT["degree",0.0174532925199433]],
    CS[ellipsoidal,2],
        AXIS["geodetic latitude (Lat)",north,
            ORDER[1],
            ANGLEUNIT["degree",0.0174532925199433]],
        AXIS["geodetic longitude (Lon)",east,
            ORDER[2],
            ANGLEUNIT["degree",0.0174532925199433]],
    ID["EPSG",4326]]
Data axis to CRS axis mapping: 2,1
Origin = (-55.043315251243307,-58.879481151356849)
Pixel Size = (0.000179663056824,-0.000179663056824)
Metadata:
  AREA_OR_POINT=Area
  TIFFTAG_RESOLUTIONUNIT=1 (unitless)
  TIFFTAG_XRESOLUTION=1
  TIFFTAG_YRESOLUTION=1
Image Structure Metadata:
  COMPRESSION=LZW
  INTERLEAVE=BAND
Corner Coordinates:
Upper Left  ( -55.0433153, -58.8794812) ( 55d 2'35.93"W, 58d52'46.13"S)
Lower Left  ( -55.0433153, -63.8954940) ( 55d 2'35.93"W, 63d53'43.78"S)
Upper Right ( -44.5233246, -58.8794812) ( 44d31'23.97"W, 58d52'46.13"S)
Lower Right ( -44.5233246, -63.8954940) ( 44d31'23.97"W, 63d53'43.78"S)
Center      ( -49.7833199, -61.3874876) ( 49d46'59.95"W, 61d23'14.96"S)
Band 1 Block=496x384 Type=Float32, ColorInterp=Gray
  NoData Value=0
  Metadata:
    STATISTICS_VALID_PERCENT=0

Could someone explain why this occurs? I’m new to SAR image processing so kindly let me know if my workflow is incorrect.

Issue Analytics

State:
Created 3 years ago
Comments:11 (6 by maintainers)

Top GitHub Comments

1reaction

johntruckenbrodtcommented, Sep 17, 2021

Hi. I discovered that SNAP has an option to use the GETASSE30 DEM. This is in 30 arc seconds resolution, so quite low, but it is fully global (i.e. also covering oceean areas). This is great because there is no need to adjust the pyroSAR.snap.geocode workflow with these Ellipsoid-Correction operators (which are quite limited anyways).

from pyroSAR.snap import geocode

filename = S1A_EW_GRDH_1SSH_20200317T225506_20200317T225606_031721_03A873_CB43.zip
outdir = "./outdir"

geocode(infile=filename, outdir=outdir, terrainFlattening=False, nodataValueAtSea=False, demName='GETASSE30')

This seems to be a very good solution so I am closing the issue. Feel free to re-open if there is more to it.

1reaction

johntruckenbrodtcommented, Mar 5, 2021

Great! With the current master branch this “hacky modification” is no longer needed. Let’s leave it open so I can integrate this into ‘geocode’ later. No idea when it will be though.
Thanks a lot for your help!