Users should be aware that ERS-2 SAR products from January 2001 onwards were acquired under degraded attitude conditions following the gyroscope failure in January 2001. Following this failure, an attempt was made to pilot without the use of gyroscopes ("gyro-less piloting mode" or Extra Backup Mode (EBM) from January 2001 to June 2001). During this period the image location may be displaced with respect to the nominal scene location by up to +/- 5 km in range and up to +/- 30 km in azimuth.
Following the EBM period a succession of improvements were implemented from June 2001 onwards, during which the attitude performance was progressively improved. Although Doppler Centroid frequency was still unstable, the maximum mispointing was significantly reduced. Improvements implemented in March 2002 marked the best attitude stability since January 2001.
More details can be found here and in the paper "Review of the Impact of ERS-2 Piloting Modes on the SAR Doppler Stability".
We recommend that users exercise caution when using ERS-2 products from January 2001 onwards and if necessary perform their own detailed analysis. Due to the very high and unstable Doppler Centroid frequency, use of data from this period for InSAR applications is not recommended.
Product disclaimer for SAR data from the ERS commissioning phases:
Please note that all ERS-1 SAR products from 27/07/1991 to 10/12/1991 and all ERS-2 SAR products from 07/05/1995 to 17/08/1995 were acquired during the commissioning phases of each satellite. Users should be aware that data products acquired during commissioning may be of reduced quality, due to platform and instrument operations.