A standard index of spatial resolution for distributed targets in synthetic aperture radar imagery

In this article we outline the need for a consistent method of quoting synthetic aperture radar (SAR) resolution given the influence of speckle upon SAR images. Standard measures of resolution depend upon the separability of point targets; however, this is not a useful analogy in the context of SAR. We contend that quoting resolution for a 3-4-look product may be unrealistic given the influence of speckle. Our approach considers the separability of targets that differ in intensity by a known contrast ratio, with a ratio of 2, that is, 3 dB difference, used as the threshold value. It is demonstrated that 12 looks represents a more realistic estimate of the capabilities of the system and should be used to quote an equivalent spatial resolution (ESR) when describing potential instrument performance.