Actual resolution of Sentinel-1

Dear colleagues,

Can anyone explain what is the actual spatial resolution of Interferometric Wide Swath Sentinel-1 GRD data?

I read and found inconsistent descriptions on the resolution of this Sentinel-1 product in the below links:

1- Interferometric Wide Swath has 250 km swath, and 5 x 20 m spatial resolution

2- Sentinel-1 at the High resolution Level-1 GRD, IW mode (see the table 2)

  1. is correct for GRD-products and 1) for SLC-products.
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Thanks Mengdahl,

The data was collected at 5 x 20 m resolution (1); and it reduced to 20 x 22 m after processing (2).

So we should say the Spatial Resolution of Sentinel-1 is ~ 20 x 20m?

By the way, could you explain what the Number of Looks and Equivalent Number of Looks (ENL) are?


Dear giangnv,

The spatial resolution of IW GRD products depends as well on the type of GRD with reference to

For GRD Medium Resolution, this is 88 x 87m
For GRD High Resolution, this is 20 x 22 m

Other modes and processing levels have different resolution.

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Dear Giangv,

The products are either available as Single Look Complex (SLC) or Ground Range Detected (GRD) processing levels.
The main difference between the two is that for GRD products, a processing of multi-looking is applied.
This process is an averaging of “sub looks” computed from the full resolution SLC data. Each sub look is “detected” before the averaging (thus the D in GRD).
The Equivalent Number of Looks (ENL) is intended to correspond to the number of equally-weighted, statistically independent looks which would produce the same speckle statistics as the processing used to generate the product.
The ENL will normally be less than the total number of looks, NL, because of partial overlapping of the looks and unequal weighting.
You can here refer to:

Using multi looking allows to improve the speckle statistics, but reducing the resolution.