Usually, in traditional Inverse Synthetic Aperture Radar (ISAR) systems design and
mode selection for space satellite targets, coherent integration gain in azimuth direction
hardly can be analyzed, which depends on target’s motion. In this study, we combine
the target orbit parameters to determine its motion relative to radar and deduce coherent
integration equation in ISAR imaging to realize the selection of imaging intervals
based on coherent integration, which can ensure the resolution in azimuth direction.
Meanwhile, we analyze the influence of target orbit altitude to echo power and imaging
Signal-to-Noise Ratio (SNR) that provides a new indicator for space observation ISAR
systems design. The result of simulation experiment illustrates that with target orbit
altitude increasing, coherent integration gain in azimuth direction of large-angular
observation offsets the decreasing of imaging SNR in a degree, which provides a brand-new
perspective for space observation ISAR systems and signal processing design.