I am working with Sentinel-1 images. at this time I am focusing on S1-GRD products.

Based on the Sentinel-1 dodumentation we know that GRE images are the same SLC images which have gone through different preprocessing steps. and unlike SLC products whose pixels are "rectangular" the pixels of GRD after some projections and resampling steps are approximated to "square" ones and we assume that they have 10x10 pixel spacing (and we know that pixel spacing is not the same as pixel resolution).

Now When I use GDAL to access some information from metadata, I see that:

Origin = (5.807367830419758,47.316947720266072)

Pixel Size = (0.000112597613697,-0.000113573780624)

Here I believe that by "pixel size", GDAL actually means "pixel spacing" and I assume that those two long lines of floating values are equal to (10,-10) in meters.

What "units" are these long floats defined in and based on what calculation can I turn them into meter units?

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    As you said. Pixel size in standard GIS world means resolution. But in SAR resolution is how far the objects must be from each other to distinguish them. So yes >>> pixel spacing (SAR) is pixel size (GIS). – Jan Doležal Dec 10 '19 at 10:04

The unit is degrees longitude and latitude, which is a result of your georeference system being epsg:4326.

Pixel size and pixel spacing are used interchangeably, as the concept of overlapping pixels is generally ignored.

The best way to convert the numbers to meters would be to reproject your data into a more suitable coordinate system, such as the appropriate UTM system. Assuming that your data is located in Switzerland (5.6 lon, 47.3 lat), which I suspect given your coordinates, the appropriate UTM system is 32N, with the epsg number 32632.

As for the authority fields in the WKT-string that was posted in the comments. The first two 'authorities' relates to the spheroid. 7030 and 6326 both refer to the WGS84 spheroid, which is to say that the coordinates relate to one specific representation of the earth. The third 'authority', is 4326, which specifies that the raster is in "geographical coordinates", meaning latitude and longitude.

  • Thank you very much for these good information. Now I understand (as I always suspect) the importance of the correct definition of the coordinate system! :) – user1771806 Dec 10 '19 at 10:20
  • Just a side issue with your Assumption. My data does not belong to "somalia". It belongs to the UTM tile 32T which covers an area around the Lausan Lake in Switzerland. This definition of UTM/EPSG is still something blure to me. The fact that the Metadata of each S1-tile contains "more-than-one" EPSG code, I have this constant difficulty to correctly define the coordinates of my data within different Spatial Reference Systems. Hear I print the SRS information of my S1 tile : – user1771806 Dec 10 '19 at 11:03
  • Coordinate System is: GEOGCS["WGS 84", DATUM["WGS_1984", SPHEROID["WGS 84",6378137,298.257223563, AUTHORITY["EPSG","7030"]], AUTHORITY["EPSG","6326"]], PRIMEM["Greenwich",0], UNIT["degree",0.0174532925199433], AUTHORITY["EPSG","4326"]] Origin = (5.807367830419758,47.316947720266072) Pixel Size = (0.000112597613697,-0.000113573780624) As you can see there are " different AUTHORITY fields containing different EPSG codes. and I am still confused in their interpretation. – user1771806 Dec 10 '19 at 11:07
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    @user1771806 Please do not add thanks comments (covered by help page ), and please do not pose new questions in comments – Vince Dec 10 '19 at 11:42
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    @user1771806 - I updated my answer to reflect your comments and answer your follow-up question. – Mikkel Lydholm Rasmussen Dec 10 '19 at 11:45

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