ERS-1 was launched in July 1991 with its primary instruments being an active microwave instrument (AMI), a radar altimeter, an along-track scanning radiometer and microwave sounder. The AMI comprised two seperate radars - a Synthetic Aperture Radar (SAR) and Wind Scatterometer. These enable three modes of operation - Image Mode, Wave Mode (both performed by the SAR) and Wind Mode (performed by the Wind Scatterometer).
The ERS-1 mission ended in March 2000. Full details of the ERS-1 mission can be found here.
The ERS-1 acquisition plan and the various modes of operation are provided here. The standard operational mode provided a 35 day repeat orbit. During the early part of the ERS-1 mission other repeat periods were used: an ice mode (3 day repeat), geodetic mode (168 day repeat) and tandem mode (joint interferometric mode with ERS-2).
An example plan for February 1996 is show below: