1

I have been processing Sentinel-1 SAR images-both medium and high resolution. Looking into the documentation, the pixel spacing and resolution have been specified as:

High resolution level-1 GRD:

EW Swath -

  1. resolution = 50x50 m
  2. pixel spacing = 25x25 m

IW Swath -

  1. resolution = 20x22 m
  2. pixel spacing = 10x10 m

Medium resolution level-1 GRD:

EW Swath -

  1. resolution = 93x87 m
  2. pixel spacing = 40x40 m

IW Swath -

  1. resolution = 88x87 m
  2. pixel spacing = 40x40 m

However looking at the image, when I measure the length of the pixel, it is equal to the pixel spacing for both high and medium resolution images which is 10 m and 40 m respectively.

The images are shown below:

enter image description here enter image description here

It is a level 1 GRD product. The high resolution image is in IW swath and the medium resolution in EW swath.

  1. Is it then correct to say that the spatial resolution is 40 meters for medium resolution in EW swath, and 10 meters in IW swath?
  • Spatial resolution is a measure given by those who know their instrument and its capabilities. You can split the pixels but that does not change the real resolution. – user30184 Jul 22 '18 at 7:43
  • Thanks for your answer. Is there a way to measure the spatial resolution in this case apart from the documentation of the product? – webapp Jul 22 '18 at 15:00
  • Not directly but I suggest to read en.wikipedia.org/wiki/Angular_resolution. If you find a specially built test-field from your satellite image you could perhaps use that but test-fields are rare. Some reading about camera calibration isprs.org/proceedings/XXXV/congress/comm1/papers/8.pdf. – user30184 Jul 22 '18 at 15:49
  • Okay. How do we then measure area of an object in the image? Since pixel spacing is actually the size of the pixel and not spatial resolution. – webapp Jul 22 '18 at 21:32
  • 1
    You count the pixels, what else? If you see that a building is presented by 5x5 black pixels, 10 by 10 m each you know that the building is about 50 by 50 meters. Same result if you have 10x10 black pixels, 5 by 5 meters each. Where the spatial resolution has role is that if spatial resolution is, lets say 100 meters, you cant find the building from the image at all. – user30184 Aug 2 '18 at 19:55
2

There is information about the spatial resolution (as distinct from the sampling rate) for Sentinel 1 in the technical guide. Most of the data (viz. hi-res GRD in IW mode) is roughly 20m spatial resolution, but is provided with 10m sampling.

  • Thanks Benjimin, this distinction was needed to resolve the doubt. – webapp Oct 25 '18 at 19:15

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