ABSTRACT
Researchers in geography are much interested in issues of scale and resolution, and the strong influence these may have on the results of analyses of spatial patterns (Harvey, 1968; Stone, 1972; Goodchild and Quattrochi, 1997). Issues of scale usually arise from not knowing the optimal unit size for a study area; while MAUP (the Modifiable Area Unit Problem), one of the fundamental research problems in geographical information science, can also be considered to be related to the understanding of the scale for spatial data (Openshaw, 1984; Fotheringham and Wong, 1991). GIS and remote sensing have shown active interests in both the operational scale and measurement scale of data. Technological developments in GIS and remote sensing have led to the gradual detailing and elaboration of the measurement scale. In the field of remote sensing, for example, the 78m resolution Multi-Spectral Scanner (MSS) data of the 1970s has given way to 30m Thematic Mapper (TM) data in the 1980s, SPOT in the 1990s, and 1m IKONOS imagery in the 21st century. Such improvements in the measurement scale will allow for the new understanding of geographical phenomena that could not be measured at the previous scales. Changes of the ground resolution of satellite imagery have modified the inherent characteristics of imagery due to the "scale effect" (Goodchild and Quattrochi, 1997). Therefore, researchers have to select the image with the optimum resolution among the satellite imagery at diverse resolutions, at which a specific geographical phenomenon can be understood more effectively. In order to explore the optimum resolution, the objective procedures or indices must be designed for the image characteristics at different resolutions. They should be able to represent the changes in image characteristics that occur at different resolutions. The aim of the present study is to propose a procedure for identifying the optimum resolution for the study of coastal wetlands. These wetlands, as the point where the ecosystem of the land meets the ecosystem of the ocean, have unique
and diverse topographical features, giving rise to the formation of vegetation colonies, and exhibits diverse spatial distribution due to diverse environmental factors. Due to the dense vegetation and unstable topography of the coastal wetland, it is more effective to use satellite imagery to understand its characteristics, rather than through field investigation (Lyon and McCarthy, 1995). However, it is not necessarily effective to use the satellite imagery of higher ground resolution in the coastal area. For example, in the case of the salt marsh where colonies appear as clusters, the use of low-resolution imagery of the approximate size of the clusters is more effective (McNairn et al., 1993). In this vein, this study will attempt to find procedures and techniques for the optimal spatial resolution of satellite imagery in the study of coastal wetlands. To achieve this goal, it firstly selected the indices considering the following conditions: (1) the sensitivity of the indices, which change in response to the different resolutions, should be high enough to respond accurately to the changes in image characteristics; (2) the indices should be the ones that can provide the approximate estimate of the final result only with the minimal procedure; (3) the indices should reflect the classification accuracy of the attribute information. We then coarsened the resolution of the satellite data, to produce images at various resolutions, and observed the changes in the textural and attribute information characteristics of these images at various resolutions. As a result, the study was able to decide the operational scale, an optimum resolution in the use of satellite imagery.
