# Why is azimuth resolution worse than range resolution in Sentinel1 (SAR) [duplicate]

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`.

• @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`. Aug 5, 2015 at 21:12
• 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. Aug 6, 2015 at 13:14

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?). Aug 7, 2015 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, 2015 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!). Aug 14, 2015 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, 2015 at 7:54