Sentinel-1A GRD product

Speckle filtering reduces noise-like patterns in your image.
Terrain correction reduces gemetric distortions due to the side-looking geometry of your system.

How would i know about an image whether it has thermal noise or not?


in fact, it always has some. If you don’t de-thermal noise, the image is ok although this step would improve performance in most case

is it necessary to convert sigma0 values to dB ? can i do log transformation on my own e.g in R ?

yes, you can do that later as well. Also it is not mandatory, it just stretches radar backscatter over a more usable range which have nearly a gaussian distribution.


I am getting only positive value of sigma nought (db) in VV intensity (my image is S1A GRD L1 product)

Can you please share a histogram of your data?

Hi Iveci,
Your explaination is very useful.
I have another question for GRD product preprocessing. Since the sigma 0 is in intensity scaling, if Iwant to get the radiometrically calibrated value of amplitude, can I directly calculate the square root the sigma 0 values?

Many thanks for your reply!

Hi, All radiometric measurements from detected SAR imagery (such as Sentinel-1 GRD products) should use intensity values and not amplitude. So radiometrically calibrated value of amplitude is not a physical quantity and it should not be used.

FYI, the only reason why detected products include amplitude values is so that the dynamic range of the processed SAR signal can fit into the 16bits of the product. If intensity values were included in the product, 32 bits would be required per pixel and so the product would be twice the size.


I understand, thank you very much!

Hi valgur,
Thanks for the document.I have read the document, but when I want to select any particular value in the look up table how could I proceed…
Actually my reflector area lies in 6776 line ,12185 pixel no approx. N Grdh is having 16586 lines and 25867 pixels in each line so how to reach my line n pixel value.I ve verified the calibration vector list… nearest vectorlist line is 6716…I am really confused anyone pls help me in this regard…
If I need to locate based on azimuth time where will I get exact azimuth time of my target…
Thanks in advance