Dear Md Nowfel Mahmud Bhuyian

Please find this paber it will help

Article A Method for Automatic and Rapid Mapping of Water Surfaces f...

Dear Nowfel,

To map water body using Sentinel-1 SAR C-band data do the following:

Using SNAP Sentinel-1 do the following:

1- Calibrate the image in SNAP Radar / Radiometric / Calibrate

Convert S0 to decibel (logarithmic scale)

2- Filter speckles in SNAP Radar / Speckle Filtering / Single Product Speckle Filter "LEE filter". In “Filter Size X:” and “Filter Size Y:” select 5, and 5 respectively

3- Geocoding / Terrain Correction 9.1. Radar / Geometric / Terrain Correction / Range-Doppler Terrain Correction

4- Compute histogram Analysis / Histogram

Select “Bands” folder in “Product Explorer” window and select “Sigma0_VV_db” by clicking on band name.

Click on “Refresh View” button. You might see a small second peak between around -20 and -25 db. These are backscatters for water bodies.

5- To extract water bodies, we will apply a simple threshold to VV backscatter

Mask out the areas by selecting Raster / Band Maths / Edit Expression.

In the “Expression” window, type “Sigma0_VV_db < -20”.

Save the newly created virtual band to the actual band by right-clicking on the band and selecting “Convert band”

You can see that some single bright pixels in the lake are classified as non-water. You can apply a lower threshold (e.g., -19 db).

(Source ESA)

Hi there,

Separation of water has been quite straightforward using thresholding, simple discrimination or machine learning coupled with Sentinel-1 GRD data. The real question is how you would define waterbodies. With sort of conditions, GRD data are often challenged with shallow inundation. Using SLC data (where you could combine Backscatter with HAA features) somewhat helps if it is the case. But again, let's get back to the definition.