Limitations on SAR Image Area Due to Motion through Resolution Cells

Range-Doppler imaging systems are degraded by the motion of an object through its resolution cells during image formation. Given the range resolution dR, the cross-range (azimuth) resolution dA, and the wavelength λ, the image's range extent DR and cross-range extent DA must be constrained by λDR ≤ 4d2A; ≤DA ≤4dAdR to avoid significant image degradation. By implication, we can image a rectangular area A ≤ DADR. We show that, in general, the acceptable image area is a parallelogram which becomes a rectangle only in the special case of unsquinted, broadside operation. Furthermore, the actual useful image area within a rectangular map of range extent DR and crossrange extent DA decreases as the squint angle measured from broadside increases.