This paper presents four imaging approaches for terrain observation by progressive scans (TOPS)-mode SAR focusing, all of which take advantage of modified chirp scaling (CS) algorithms according to echo properties in TOPS. After adopting different azimuth preprocessing steps to resolve the aliased Doppler spectra, the resulting TOPS raw data can be handled by a classic CS processor. Unfortunately, the resulting images would appear back folding, if only a standard stripmap processor is adopted. To avoid or resolve azimuth back folding in the final focused TOPS SAR images, four modified CS algorithms are presented according to special properties of the slow time-frequency diagram in TOPS. Imaging results on point targets validate the presented imaging approaches.