I would suggest these steps:

1. Generate the fishnet grids using the extent of one of the raster with fine resolution.

2. Use that fishet as sampler and extract the values of both of your rasters. Now you have table with dependent and independent variables.

3. Now run OLS tool in ArcGIS. It will generate the equation. Lets say your equation is biomass=a*NDVI+c

4. Go to raster calculator and use that equation generated above and you get the new raster, which will be your biomass.

Hope it helps.

I support Sita suggestion!

best regards,

Dear Saulo,

just a supplement to Sita Karki 's suggestion: you can perform kriging using the Geostatistical Wizard (or any other type of interpolation method) on the residuals resulted from the Ordinary Least Squares tool. OLS+kriging is almost the same as regression kriging (which is not implemented in the older versions of ArcGIS).

Or also see this tutorial video about Regression Kriging Toolbox for newer versions: https://www.youtube.com/watch?v=uDWBT1wn8Ps

HTH,

Ákos

Dear Colleagues

Thank you for the help!!

Best Regards,

Saulo

Also you can use GWR for Raster Downscaling included in SAGA.