A Standard Index of Spatial Resolution for Distributed Targets in Synthetic Aperture Radar Imagery I. H. WOODHOUSE * , A. MARINO, I. CAMERON School of Geosciences, The University of Edinburgh, Drummond St Edinburgh, United Kingdom, EH8 9XP In this paper we outline the need for a consistent method of quoting 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 looks 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, i.e. 3 dB difference, used as 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 1. Introduction The increasing availability over the last decade of both space-borne and airborne high resolution radar systems has given the user community an ever wider selection of observational tools. However, this abundance of choice has a new problem – users must be able to easily assess the data quality and compare performance across sensors in a straightforward and transparent manner. In this paper we address one aspect of this problem, particularly within the field of land surface applications of radar imagery, by tackling the issue of spatial resolution. It is the experience of the authors that spatial resolution of radar imagery is neither presented consistently across data providers, nor is it widely understood by users of the data. Inconsistency and confusion often leads to inappropriate application and eventual disappointment on behalf of many users. Spatial resolution is a key performance indicator of remotely sensed imagery and is defined as the separability of two idealised point targets. The point target is characterized by a Dirac delta function and so does not indicate visibility, which is a property of the contrast of any individual target with its background. The limiting factor of any imaging system is therefore the width of the end-to-end point spread function (PSF), or more exactly the ability to separate two overlapping PSFs. Separability usually refers to the distance between the maximum and the first minimum in the point spread function, although there are other arbitrary criteria that can be used to decide at what point they are separable. The problem in radar imagery is that speckle, the noise-like modulation of the signal due to wave interference, does not effect point targets. The strict definition of spatial resolution does not allow direct comparison between differently processed SAR data, nor between *Corresponding author. Email: i.h.woodhouse@ed.ac.uk