Dear Pradeep Sir,

You can use SNAP software to convert DN to dB. There is number of equation being used to convert DN to dB based on their characteristics so it will better to follow the sentinel 1A handbook. in that case you can use this equation also

dB= 10* log (DN).

Thank you so much for your soon reply. Can you suggest any good link for the equation.

Hii Pradeep..

It is very important that the prior to processing the microwave satellite images (SAR data), you have to identify which parameter is sensitive to microwave region (C-band in case of Sentinal 1A). Then accordingly you can apply different data processing steps on to it. The SNAP toolbox is very good software to process the Sentinal data. The conversion of intensity to dB values is straightforward there. You can you Band Math operation or right click on intensity and convert in to dB. I am attaching a file here you will get the IDEA that how to processes the Sentinal 1A data (In my case application is flood extent extraction).

I agree with Avinash, the eq is dB= 10* log (DN). However, you should also consider Amids suggestion. Before you can convert DN to dB you must to radiometric calibration, multilook, speckle reduction or speckle filtering, and terrain correction. Good luck

Thank you so much for your reply Amit Kumar Dubey and Gordana Jovanovska Kaplan

Dear Pradeep, how are you..

σ0 (dB) = 10*log10 (abs (σ0))

Where, σ0 (dB) – backscattering image in dB

σ0 – Sigma naught image.

Thanks dear Iyyappan

After performing the following processing on sentinel 1using SNAP

1. Radiometric calibration 2. Speckle filtering

3. Terrain Correction (i prefer Range-Doppler Terrain Correction)

Each of these steps would give you a new file. The new file will be the input for the next step. From the new file generated after step 3, clickon bands and right click you would see 'Linear to/from DB'

σo = 10 * log10(DN2) + K

Thanks Janaki Sandamali

The equation is γ₀ = 10log₁₀(DN²) - 83.0 dB