Coordinates disappear when exporting SAR data

[waqasqazi]

Hi,

I’ve been seeing this issue with Sentinel-1 Toolbox / SNAP: When I open SAR data, such as Envisat or ALOS-1 PALSAR, and try to export it into any other format, like ENVI format or GeoTIFF, the coordinates are not taken with the export. The ENVI format .hdr file does not have any spatial reference in it. When I open the exported ENVI file or GeoTIFF file in any other software, it shows me the data, but there are no coordinates.

Am I doing something wrong with exporting? What’s going on?

Cheers,
Waqas.

[ABraun]

SNAP interprets the geocoding information of the SAR metadata. But in most cases the data itself is not projected yet.
You need at least to apply a map projection first before exporting the SAR data.

Which data are you using? Which product level? SAR data often comes in SLC / L1 level which is not projected yet. Please also see here:

GTC (Geocoded terrain corrected) data

it means that its already ground-range corrected. Unlike SLC data the pixels' areas are already of same size. Astrium has made nice graphics for this case. They refer to TerraSAR-X but the principle is the same for most SAR satellites: Slant Range Complex (SLC/SSC/L.1.1) [image] Data is neither multi-looked nor projected Ground Range Detected (GRD/MGD/L1.5) [image] Data is multi-looked but not projected Geocoded Ellipsoid Corrected (GEC/L2.0) [image] Data is projected but topographic di…

[waqasqazi]

ABraun, thanks for you reply. I am using intensity data, so it is already detected data and not SLC/L0. I am using Envisat ASAR Precision Mode .N1 format intensity data (.IMG/IMP format with coordinates), and ALOS-1 PALSAR Level 1.5 CEOS data. I understood your point as valid, but it took me some time to figure out how to actually re-project the data, as some tools did not apply. Finally, I’ve figured this out:

For Envisat ASAR IMG/IMP .N1 data, apply the Radar > Ellipsoid Correction > Gelocation-Grid function. I exported the output in ENVI format, and opened in ENVI, this time the coordinates are attached.

However, for ALOS-1 PALSAR Level 1.5 CEOS data, the Geolocation-Grid function does not work, as it says “Source product should not be map projected.” I tried to use the Radar > Geometric > Update Geo Reference function instead, which requires DEM to be provided or will auto-download. This function works and generates output, however this output again does not contain the coordinates when exported to ENVI or GeoTIFF formats. I also tried the Raster > Geometric Operations > Reproduction tool, but that says “SAR products should be terrain corrected or ellipsoid corrected.” So I am stuck with the ALOS data.

So the question now is: How to export coordinates for ALOS-1 PALSAR Level 1.5 CEOS data? If SNAP says "Source product is already map projected, why dose it not export the coordinates in any format?

[ABraun]

For most cases the “Range Doppler terrain correction” should be sufficient.

However ALOS Level-1.5 data is a bit tricky. Have a look here:

ALOS-1 L1.5 Terrain Correction

Dear users, The ALOS-1 L1.5 images are already map projected (GRD), but are not terrain corrected (orthorectified). All the SNAP tools in "Terrain Correction" or "Elipsoid Correction" do not work with the L1.5 images and give as error: "Source product should not be map projected." So, how may we orthorectify those images using SNAP? Best regards, Gustavo

Alos 2 Geo-reference

Hi, thanks for the quick reply. I'm not sure if 1.5 NOT map corrected are an option? Too late to get different products anyways, we've already ordered and downloaded our quota for the year. I'll investigate the Geomatica option for now. Cheers!

[waqasqazi]

Thanks, the SAR-Mosaic with only 1 image as input trick works for ALOS-1 PALSAR!

[waqasqazi]

Having the same issue with TerraSAR-X data, and this time the “SAR-Mosaic with only 1 image” trick does not work either. Anyone has faced the same problem? I am using standard TerraSAR-X EEC(Enhanced Ellipsoid Geocoded) intensity GeoTiff product.

[ABraun]

ENVI has a TerraSAR-X reader but I don’t know much about it.