provide a short revisit time (around 3 days) and have stereo mapping capability. In particular, stereo pairs can be formed in near real time due to a very flexible pointing mechanism. These characteristics make these new high-resolution satellite imagery systems very attractive for monitoring and change detection as well as coastal mapping.

If ground control is used, IKONOS images are capable of producing mapping products with meter position accuracy for general land features and submeter accuracy for objects that can be measured at subpixel level (Di et al., 2003). Although the sensor model is not provided to the users, so-called rational function coefficients are supplied along with stereo imagery to allow generation of Digital Elevation Models (DEMs), orthoimages, and other features. Recent results of tests and experiments to use IKONOS images for coastal mapping have demonstrated the potential to produce shorelines with about 1-meter horizontal and 2-meter vertical accuracy (Li et al., 2002). Since a satellite system has a prescribed orbit, it is impractical to require that the satellite images be taken at the time of a local MLLW or Mean High Water (MHW) level. Shorelines extracted from IKONOS images are therefore always instantaneous shorelines. In conjunction with an accurate Vdatum model, however, instantaneous shorelines can be converted to more traditional tidal datum-based or orthometric shorelines. Accordingly, high-resolution satellite imagery appears to have considerable potential for augmenting or replacing aerial photogrammetry in coastal mapping. There are numerous online resources already available that provide access to aerial- or space-derived imagery. These include the USACE Topographic Engineering Center’s Commercial and Civil Imagery Office,1 the USGS Global Land Information System,2 and the Microsoft TerraServer web site.3



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