Ramp response radar imagery spectral content

The physical optics (PO) approximation is examined in the time domain to illustrate certain relationships between an area function interpretation of the physical optics scattering estimate and the span of interrogating frequencies required to produce an image of the object. The consequences of extending the normal physical optics integration limit to encompass the entire object are demonstrated using conducting spheres, disks, cone spheres, and hemispherical objects. Low frequency interrogating signals are stressed for imaging purposes with an interpretation of when such signals must be supplemented by higher frequencies.