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Why is the azimuth resolution in Sentinel (SAR sensor) worse than the range resolution?

The table in this link gives the resolution for SLC products aquired in the different aquisition modes.
In all of them the range resolution is better than the azimuth resolution.

Note: This question is totally different from my previous one, as the latter tackles the effects of the incidence angle on the ground resolution (range resolution + azimuth resolution), and this doesn't explain why sometimes the range resolution is better than the azimuth resolution.

marked as duplicate by MappaGnosis, Simbamangu, Brad Nesom, Mapperz Aug 11 '15 at 17:39

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • @Vince No, in the previous topic it's not explained why azimuth resolution is worse than the range resolution, just that the overall resolution is affected by the incidence angle. – Hakim Aug 5 '15 at 21:12
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    It still has to do with the geometric setup of that particular sensor and what the terminology means. You should check out a remote sensing primer such as Jensen or other authoritative text. @Vince is correct. – Chris Strother Aug 6 '15 at 13:14
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It's normal that azimuth and range resolution of SAR sensors differ, because they depend on different variables:

  1. The azimuth resolution (AR) of a SAR system is: AR=Length_of_antenna/2

  2. The slant range resolution (SRR) of a SAR system is: SRR=(Speed_of_light*pulse_length)/2

  3. The ground range resolution (GRR) of a SAR system is: GRR=SRR*(1/sin(look_angle))=SRR*(1/cos(depression_angle))

The SRR is independent of the height of the satellite/airplane or the look/depression angle. The GRR depends on the look/depression angle: the GRR decreases with larger slant-range distance.


References:

  • http://www2.geog.ucl.ac.uk --> ! I think this is wrong: "Note the range resolution is infinite for vertical look angle and improves as look angle is increased"

  • Lillesand, T. M., Kiefer R. W. & Chipman J.W. Remote sensing and image interpretation (7th ed.), 2015, p 396

  • http://www.nrcan.gc.ca

  • Thanks for the equations and the link. I'm a little bit confused, in the link you gave (according to ground range equation), the ground range resolution improves with increasing angles; whereas im my previous question, it is said that an increasing angle engender an increase in the swath width which causes a decrease in the resolution (or do they mean it's just the azimuth resolution that is decreased in this case?). – Hakim Aug 7 '15 at 14:18
  • I think there is an error in the first reference I linked, thus, I updated my answer: The SRR remains constrate with range, the GRR decrease with ranges. I highly recommend: Lillesand, T. M., Kiefer R. W. & Chipman J.W.: "Remote sensing and image interpretation" for a better understanding of SAR imagery! – Iris Aug 9 '15 at 18:24
  • According to the formula of the range resoultion, I'm reading on Jensen - Remote Sensing of the Environment book, there's a small error in your second equation, it should be: SRR = pulse_length / 2 = (c * τ) / 2. And as a result, the range resolution in the far range is better than in the near range (which is weird!). – Hakim Aug 14 '15 at 14:13
  • @h4k1m, I think there is an error in the reference Jensen. Look here is an other example with the formulas and the example of ERS SAR: topex.ucsd.edu/rs/sar_summary.pdf – Iris Aug 31 '15 at 7:54

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