Calling linear to converted dB bands and creating few more bands such as VV/VH, VH/VV, VV+VH in function using Google Earth Engine

Question

My question is similar to:

• Radar Vegetation Index Using Google Earth Engine
• Convert Sentinel-1 images data from dB to linear

I am new to GEE and JavaScript.

I want to create the following number of bands for each Sentinel1 scene other than original bands (vv,vh in linear scale).

1. RVI, NRPB, VV-db, VH-db, VV/VH (db), VH/VV(db), VV+VH (db).

//// RVI calculation
var RVI = vvVhIw.map(function (image){
  var rvi = image.expression('sqrt((vv)/(vv+vh)) *  ((4*(vh))/(vv+vh))',
    {'vv': image.select('VV'),
     'vh': image.select('VH')
    }
    );
    return rvi;
  });

// calculate NRPB Band
var NRPB = vvVhIw.map(function (image){
  var nrpb = image.expression('(vv-vh)/(vv+vh)',
    {'vv': image.select('VV'),
     'vh': image.select('VH')
    }
    );
    return nrpb;
  });
  

// convert Linear to DB
var TO_DB = vvVhIw.map(function (image){
  var to_db = image.expression('10 * log10(linear)',
    {linear: image.select(['VV','VH']),
    }
    );
    return to_db;
  });

How to call the VV and VH bands that are in decibel in a function to create bands such as VV/VH (db), VH/VV (db), VV+VH (db). At the end, I will have 7 bands for each Sen1 image.

Answer 1

To begin with, you might want to start off your processing in linear, and convert to dB in the last step. For that, use COPERNICUS/S1_GRD_FLOAT. Otherwise, you convert with this:

ee.Image(10).pow(db.divide(10))

Inspect a pixel in this script to verify that the collections and conversions looks as expected.

https://code.earthengine.google.com/8c613c15465708757872505d0ca9c937