Impact of radar flightpath on synthetic aperture radar image height of focus

Synthetic Aperture Radar (SAR) projects a 3-D scene's reflectivity into a 2-D image. In doing so, it generally focuses the image to a surface, usually a ground plane. Consequently, scatterers above or below the focal/ground plane typically exhibit some degree of distortion manifesting as a geometric distortion and misfocusing or smearing. Limits to acceptable misfocusing define a Height of Focus (HOF), analogous to Depth of Field in optical systems. This may be exacerbated by the radar's flightpath during the synthetic aperture data collection. HOF is very radar flightpath dependent. Some flightpaths like straight and level flightpaths will have very large HOF limits. Other flightpaths, especially those that exhibit large out-of-plane motion will have very small HOF limits, perhaps even small fractions of a meter. This paper explores the impact of various flightpaths on HOF, and discusses the conditions for increasing or decreasing HOF. We note also that HOF might be exploited for target height estimation and offer insight to other height estimation techniques.