Bands in Sentinel 1 Level 1 (GRD, RAW and SLC) products - basic information

Microwave Toolbox
1

Dear Sentinel 1 data users.

When I open Sentinel-1 GRDH product, I see: Amplitude and Intensity.

When I open Sentinel-1 RAW product, I see: latitude and longitude only (what is usability of such product?)

When I open Sentinel-1 SLC product, I see: i_IW1,q_IW1,intensity_IW1,i_IW2,q_IW2,intensity_IW2,i_IW3,q_IW3 and intensity_IW2

Sentinel 1 L1 SLC.png646×587 22.7 KB

I can’t find any documentation, metadata, any basic information about bands stored in Sentinel-1 products.
I’ve tried to use gdalinfo tool, but it says that it is unable to open .safe file.
I can’t find proper information at http://step.esa.int/main/doc/tutorials/sentinel-1-toolbox-tutorials/

Could you tell me:

  • what are the i, q and intensity and their units, please?

  • how can I obtain sigma (backscatter)? Am I able to receive it from all Sentinel products (SLC, GRD and RAW)?

  • why backscatter is not just simply available after opening Sentinel 1 products? I thought that it is directly measured by the radar

2

See the Sentinel-1 User Guide for a description of the Sentinel-1 products and bands.
You can’t do much of anything with the Level-0 RAW products in SNAP. You need focusing software to turn the L0 to a L1 product.

Level-1 SLC and GRD products can be converted to Sigma0 using the calibration operator in SNAP.
The IW SLCs contain burst data. You will have bands for three subswaths IW1, IW2, IW3. The data is complex so you will have the real (i) and imaginary (q) parts and a virtual intensity band for convenience.

3

@lveci Thank you for quick response.
What confuses me is that you’re talking about Level0 products.

It seems that I succeeded - in case of SLC I have more bands, in case of GRDH, I receive two bands. Let me provide and example from SLC product:

Sentinel 1 SLC - sigma0 in SNAP.png1224×931 84.3 KB

Is “Radar --> Radiometric --> Calibrate” the only option which I need to apply to get backscatter for further calculations?

Should I apply also “Linear to/from dB” conversion?

4

Please consult the tutorials at https://sentinel.esa.int/web/sentinel/toolboxes/sentinel-1/tutorials

5

The SLCs and GRDs are Level-1 products. You don’t need to convert to dB to just work with the Sigma0 values.

6

How can I do that from Python?
I can’t find appropriate example in snappy package (~/.snap/snap-python/snappy/examples)

7

How to fix errors SLC to GRD with geocoded from these steps:
Read (Select Sentinel-1)
Radar -> Radiometric -> Calibration
Radar -> Radiometric -> ThermalNoiseRemoval
Radar -> Sentient-1 TOPS -> TOPSAR-Deburst
Radar -> Geometric -> SRGR
Radar -> Sentient-1 TOPS -> GRD-Post
Radar -> Geometric -> Terrain -> Terrain-Correction
Write (Select GeoTIFF-BigTIFF)

I got -3 error on screen.

8

I wonder why you even want to create a GRD out of a SLC product when you can download it directly.

1 Like
9

As I read the Document the SLC is not geocoded yet. Am I right?

10

neither the SLC nor the GRD are geocoded. They store geo-location information but are not yet projected to a coordinate system. But if you completely convert a SLC to a GRD you can download the latter instead. At least I see no benefit in doing the extra work if you don’t want to use the phase information (only in SLC), for example.

11

I would like to save the real and imaginary from SLC with geocoded.

12

I did as steps I wrote before and I got error -3.

13

I just share my opinion. I had a large data base with SLC’s and it was faster to process GRD’s from SLC than downloading them from data hub especially if you need only smaller subset of SAR image.

14

now I see…

At which step does the error occur?
If you process this with a graph try to do the steps one by one manually to see at which step the error occurs.

15

I think I got it. Thanks.

16

did you find the error source?

17

I selected complex data on Calibration but I did not select the output complex data in Terrain-Correction, that is why cost the error -3.
I just do:
Read -> Calibration ->Thermal Noise Removal -> TOPSAR-Deburst -> Terrain Correction ->write.

18

Read (Select Sentinel-1)
Radar -> Radiometric -> Calibration (select Save as complex output)
Radar -> Radiometric -> ThermalNoiseRemoval
Radar -> Sentient-1 TOPS -> TOPSAR-Deburst
Radar -> Geometric -> Terrain -> Terrain-Correction (select Save as complex output and UTM/WGS 84 (Automatic))
Write (Select GeoTIFF-BigTIFF)

Is that right way to do?

1 Like
19

I would say yes. But why do you want to save it as a GeoTiff?

20

Because, all the scientist want to geoTiff format.