This paper presents a new formulation of the Extended Chirp Scaling algorithm (ECS)1+/, suitable for the processing of data from the forward looking SAR system SIREV (Sector Imaging Radar for Enhanced Vision. This system is presently under development at the German Aerospace Center (DLR). It is shown that the SIREV data acquisition has several similarities with the ScanSAR mode of operation. Also the differences between SIREV and ScanSAR mode are analyzed. According to these differences, the ECS for ScanSAR has been modified. The modified equations of the ECS are presented and several simulation results demonstrate the good performance of the ECS for SIREV processing. The SIREV project at DLR was partially funded by STN Atlas Elektronik, Bremen. This company also holds the SIREV license rights.