CryoSat-2 and Sentinel-3 can switch between the Low Resolution Mode (LR mode) and the High Resolution Mode (HR or SAR mode), depending on the scientific and/or user needs. In order to perform this switch autonomously, the altimeters carry a mode mask. This mode mask identifies, from the coordinates of the observed scenario, the mode that has to be operated at all times.
Figure below shows the CryoSat-2 mask, also including the interferometry mode called SARin.
On the other hand, Sentinel-3 mode mask is:
fig 2. Sentinel-3 mode mask (2015, pre-launch). SAR open/closed loop (green), SAR open loop (grey), SAR closed loop (blue) and LRM (white) operating areas. It currently operates in SAR mode everywhere. Credit: ESA
Alternatively, Sentinel-6 will perform a continuous transmission of pulses with a variable PRI such as both modes (LRM and SAR) can operate simultaneously. Thus, Sentinel-6 will not have a mode mask on-board (excluding calibration acquisitions). This new operating mode is called Interleaved mode.