Sentinel-1 download

[gjs60 (Graham Sadler)]

I am downloading some small scenes (4x4km) for further analysis in ENVI software. I have used the TIFF format but this appears not to have the full meta data e.g. wavelength and acquistion date. I believe this would be found in an associated xml file. Any suggestions how to download within Sentinel Hub?

G.

[william.ray]

Hi Graham,

The full metadata is not available using Sentinel Hub Process API. You can obtain some metadata using the below function in your evalscript:

function updateOutputMetadata(scenes, inputMetadata, outputMetadata) {
    outputMetadata.userData = {"scenes":  scenes.orbits  }
}

In addition, you will also need to add an additional output in your payload called userdata in JSON format.

More metadata is available through Catalog API though. An example of an output from Catalog API in Request Builder is below:

I hope that this information helps you.

[gjs60 (Graham Sadler)]

Thank you, yes.

I have another question. I have downloaded high res TIFF images (VH and VV linear gamma orthorectified) for my 4x4km study site… For some reason they load into a 3 band image in ENVI, all with the same values. I have corrected but just wanted to confirm that I am looking at backscatter data?

G.

[william.ray]

Without having access to the evalscript that you are using to download the images or the output itself, I can’t confirm this. Are you able to share your request and evalscript?

[gjs60 (Graham Sadler)]

I have just used the standard download dialogue rather than a script. I can happily supply an example of a downloaded image but the upload feature does not seeem to available to a ‘new user’…

[william.ray]

OK can you confirm you are using EO Browser? And it should be possible for you to upload an image now

[gjs60 (Graham Sadler)]

Yes, I am using EO Browser…still can’t upload an image…

[william.ray]

Hi Graham,

I would highly advise reading the documentation surrounding the Sentinel-1 GRD data collection, as this is a complex dataset especially if you are new to SAR.

In addition, when downloading the data from EO Browser, make sure you download the Analytical product for any further analysis. Here you can specify the resolution and the product you wish to download. The basic product is only useful for visualisation purposes.

[gjs60 (Graham Sadler)]

Thank you William. I have looked at the documentation. I am using the analytical mode and downloaded these formats:

VV - linear gamma - orthorectfied
VH - linear gamma - orthorectfied

From the documentation it seemed to confirm these downloads would be backscatter measurements. I just wanted to confirm if my assumption is correct?

G.

[william.ray]

Then if the documentation confirms this, then yes your assumption will be correct

[gjs60 (Graham Sadler)]

I’m afraid the documentation is a little ambigous, focuses on script download rather than when using the UI. If you could confirm what units my choice of download will use would be much appreciated!

[william.ray]

Hi Graham,

If you are downloading the above, then the units will be to the LINEAR_POWER and your backscatter coefficient by default is Gamma0_Ellipsoid.

As specified in the documentation:

For Sentinel-1, data values are linear power in the chosen backscatter coefficient. To specify the backscatter coefficient, set BETA0 , SIGMA0_ELLIPSOID , GAMMA0_ELLIPSOID (default) or GAMMA0_TERRAIN as the value of input.data.processing.backCoeff in your request. The default is GAMMA0_ELLIPSOID .

If you are not so confident with coding but want a more specific product, then I would recommend that you try using the Request Builder application, which will help you build a request.

[gjs60 (Graham Sadler)]

Many thanks for the clarification William.