The Elevation Antenna Patterns (EAPs) used by the Sentinel-1 (S-1) Instrument Processing Facility (IPF) are derived from the S-1 Antenna Model (AM) which is able to predict with great accuracy the gain and phase patterns.
The EAP correction by the S-1 IPF was at launch only considering the gain, similarly to what was done for ASAR. As an outcome of the S-1A Commissioning Phase, it has been decided to upgrade the S-1 IPF to also compensate for the EAP phase, in order to correct for the induced phase difference between the polarimetric channels.
This correction was introduced in March 2015 with the IPF V243. As a consequence, performing interferograms between products generated with the IPFV243 and the former version V236 leads to range varying phase offset.
A new technical note explains the nature of the phase offset and provides recommendation towards its correction.