A note on spatial resolution measurement and its implications for image radiometry

Abstract

The smallest sized detail on the ground actually recorded by an airborne or satellite camera system can be different to that expected by an applications scientist or image analyst. When this misconception occurs, it may be due to the method used in determining the spatial resolution of the camera system concerned. The role of an optical system is of primary importance in setting a limit on the spatial resolution achieved by either a photographic or optoelectronic/digital camera system. This is because it is the first component of the imaging system to intercept radiation coming from an object on the ground. In circumstances where the smallest image patch produced at the focal plane by an optical system is comparable or larger in size than the pixel size/spacing of a CCD then spatial resolution will become limited by the optics, not the CCD. When this occurs, the radiometric response of the camera system to small features on the ground will correspond to the small optical image patch, and not the size of pixels in the CCD. The spatial resolution characteristics of a camera system will usually be given in terms of the ground sampled distance (GSD), or as a ground resolved distance (GRD). The results obtained by the two methods of measurement these values represent are different, and the difference can be significant because of the sampling principles that are the basis of each method.