Blue carbon estimation

Can anyone help me to estimate blue carbon of coastal mangrove area by using sentinel1 data.

That’s a quite specific request. You can start mapping costal mangroves with the approaches suggested in this tutorial: Landcover classification with Sentinel-1 GRD

This can be done for multiple dates, e.g. once per year. Then you can develop a method to relate carbon storage to the area of mapped mangroves and compare how it changed over the years.