I am using sentinel-1 image (dual-pol - VV+VH). So it has four bands, Amplitude VH, Intensity VH, Amplitude VV and Intensity VV. Is it considered as four look image? I am not understanding this properly. I want to compute ENL. Please guide me if anyone has idea.
This is not related to the number of looks. VV and VH are just two types of polarization of the wave, while Intensity is just the squared form of Amplitude. So basically they store the same information. This document might help you on the basics of SAR: http://www2.geog.ucl.ac.uk/~mdisney/teaching/PPRS/PPRS_7/esa_sar_tutorial.pdf
Regarding the ENL: http://www.securecms.com/igarss2008/abstracts/pdfs/3208.pdf
Thanks @ABraun. I will check the links in detail.