# Why pixel spacing measures as spatial resolution in Sentinel-1 SAR images

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:

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. Commented Jul 22, 2018 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? Commented Jul 22, 2018 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. Commented Jul 22, 2018 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. Commented Jul 22, 2018 at 21:32
• 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. Commented Aug 2, 2018 at 19:55