Kara Holekamp

Targets, methods, and sites for assessing the in-flight spatial resolution of electro-optical data products

The spatial resolution of a digital, electro-optical remote sensing imaging system or product is an important image quality characteristic that helps determine the utility of an imaging source. Although spatial resolution is often described by a single image quality parameter, the ground sample distance, there are several other parameters that affect image sharpness and need to be considered. These other parameters are associated with the point-spread function, signal-to-noise ratio, and dynamic range of the image product. This review paper covers the various approaches to in-flight measurement of spatial resolution parameters, including ground sample distance, point spread function, optical transfer function, modulation transfer function, far field response, and edge response and their significance, as well as target types and methods to determine these spatial resolution parameters. To this end, the paper lists and describes various targets found across the world, as well as astronomical ones. These targets are appropriate for evaluating a wide range of image scale products. For high spatial resolution imaging systems, the types of targets range from engineered fixed and deployable targets to agricultural and urban features, allowing almost any site to be used for determining spatial resolution. Independent, comprehensive image product evaluation sites that are currently in use in the US and Europe are also described.

Atmospheric correction of high spatial resolution commercial satellite imagery products using MODIS atmospheric products

Remotely sensed ground reflectance is the basis for many inter-sensor interoperability or change detection techniques. Satellite inter-comparisons and accurate vegetation indices such as the Normalized Difference Vegetation Index, which is used to describe or to imply a wide variety of biophysical parameters and is defined in terms of near-infrared and red- band reflectance, require the generation of accurate reflectance maps. This generation relies upon the removal of solar illumination, satellite geometry, and atmospheric effects and is generally referred to as atmospheric correction. Atmospheric correction of remotely sensed imagery to ground reflectance, however, has been widely applied to only a few systems. In this study, we atmospherically corrected commercially available, high spatial resolution IKONOS and QuickBird imagery using several methods to determine the accuracy of the resulting reflectance maps. We used extensive ground measurement datasets for nine IKONOS and QuickBird scenes acquired over a two-year period to establish reflectance map accuracies. A correction approach using atmospheric products derived from Moderate Resolution Imaging Spectrometer data created excellent reflectance maps and demonstrated a reliable, effective method for reflectance map generation.