I am new to sentinel-1 data. And I am trying to use images downloaded from EO for further processing, but confused with the data unit. When I download data from the EO browser, the pixel values range from 0-255, and I am wondering if they have any physical meaning?
Thanks a lot!
The data from the EO Browser is rather for visualization. It is not strictly calibrated, but ready to use in a GIS.
If you want calibrated radar backscatter, I recommend using GRD data from the official Sentinel Hub: ESA Copernicus scihub and apply calibration and terrain correction yourself: Proceedings | Free Full-Text | Sentinel-1 GRD Preprocessing Workflow
Thanks a lot for your reply, I will have a go with the sentinel hub you suggest.
And as you said the data from EO browser is for visual purpose, wondering if there is a known procedure of how the pixel values were produced?
Thanks again for your time.
They are created the same way, but are converted to Integer before the export to reduce the file size.
Thanks for the reply! But in my understanding (sorry I am new to this area), I was expecting the backscatter values to be in a typical value range or something, rather than 0-255 (that looks more like just the brightness of the pixels), would you mind correct me if am wrong?
Absolutely. But the data is rescaled during the export/download. Conversion to another file type always leads to new value ranges.
And the number are not likely to be converted back I guess…Thank you so much for the help
This would require precise information on how this stretch was performed. I didn’t find any information in the EO Browser documentation.
So you can either process the data yourself: How to Radiometrically Terrain-Correct (RTC) Sentinel-1 Data Using the ESA Toolbox – ASF
or download analysis ready data from ASF: Webinar: Sentinel-1 On-Demand RTC Processing: Generating Analysis-Ready SAR Data with ASF Vertex | Earthdata
That created the same way and are converted to Integer before the export it will reduce size of file.
Thanks a lot for the information, that was very helpful!