I need to know how to extract information from altimeter bands in sentinel-3 S3A_SL_1_RBT____20170620T081227_20170620T081527_20170621T123642_0180_019_078_2339_LN2_O_NT_002
As far as I know SNAP is focused on the optical and thermal instruments of Sentinel-3 (OLCI and SLSTR) so far. If you want to work with altimetric data extensively I can recommend BRAT:
It is also free and open source and exclusively designed for altimetric analyses. The documentation is also very good.
Yes, Andreas is right also you should use the SRAL data and not the SLSTR.
The one you are referencing is SLSTR. A altimetry product start for example with S3A_SR_1_SRA.
many thanks first , I want to confirm that is the S3A_SR_1_SRA data available for regions outside Europe