Generated composite image using Vv, vv/vh and vh as virtual red, green n blue bands and exported to geotiff uint8 . When opened exported file in arcgis, it is showing changed cell size in row direction n image looks distorted.
You may need to terrain correct before exporting to GeoTiff
Why terrain correction is required because results are good while seeing composite image in snap itself. Is it something to do with export module
Maybe ArcGis is interpreting the geo-coding information wrongly, or SNAP is writing it not correct.
Could you compare the information in both applications and report the difference?
SAR data has geocoding stored in its metadata and SNAP is designed well to read them. But If you want to locate your data in a GIS you need to write a geocoded image, either with Range Doppler Terrain Correction or (if your area is completely flat) Ellipsoid Correction.
Is Srtm OK for terrain correction or any other Dem is required? How to perform ellipsoid correction?
1 ArcSec SRTM is totally fine for most data. If you have one of better resolution, you can of course use it.
It depends on the topography of your study area how correct the terrain correction result will be.