Mismatch between pixel sizes from sentinel 1 SLC metadata and from using the measurement tool?

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#1

Hello,

I’m trying to measure distances in the range direction from sentinel 1A IW SLC images. The metadata states that the range pixel spacing is 2.33 m, however if I measure a distance in the range direction using the distance measurement tool, and divide the distance by the number of pixels I get a value of ~3.6 m. I was wondering if anyone can explain the difference?

Many thanks for your help!

#2

Good question, @junlu could you investigate?

#3

Thanks!

An example file I’m looking at is

S1A_IW_SLC__1SSV_20170204T152711_20170204T152738_015136_018C0E_12BD.zip

#4

Hi, just thought I would mention that the pixel spacing given in the SLC metadata is in slant range. Perhaps the distance measured using the distance measurement tool is in ground range?

#5

Hi Peter,

Thanks for the info, I must have missed that in the documentation, apologies!

I infer from the information given when you expand ‘details’ in the measure tool result window that the distance is calculated using latitude and longitude from the tie point grids and the mean radius of the Earth, so it gives you distance on the surface of the sphere.

The incidence angle in the example I gave above is ~38.5 degrees, which gives roughly the right ratio of slant pixel size to ground pixel size, so it all makes sense.

Thanks again!