地理情報学と地球統計学: 概要

An Updated Methodology for Preparation of Sediment Distribution Maps Using Conditional Strings in Arc GIS 10.X

RachnaPillai

This paper proposes the most simplified, concise and accurate geostatistical method for the spatial representation of the surface sediment distribution. The methodology uses conditional strings in the raster calculator of Map Algebra using ArcGIS 10.x for preparing sediment distribution maps. This methodology is an updated version of USGS Arc Map Sediment Classification since the latter is a customized toolbar for Arc GIS 9.X. The conditional strings are derived from the ternary classification systems of Folk and Shepard. These strings are further updated for mapping hard bottom along with sediment types. For generating sediment distribution map in an area with natural or artificial barriers using conditional strings in ArcGIS 10.x is also discussed here. The ‘SedTypes’ freeware attached with the paper provides conditional strings that are compatible with Arc GIS 10.X series. The freeware also provides triangular plots of sediment classifications pertaining to gravel, sand and mud (GSM) and sand, silt and clay (SSC). Further, this methodology also has several advantages over the conventional discrete number method. The spatial distribution map of surficial sediments using conditional strings is more reliable and accurate as these maps are generated taking the weight percentages of sediment classes (gravel, sand, silt, clay etc) in the corresponding rasters. The methodology using conditional strings for preparing sediment distribution map and spatial representation of hard bottom along with sediments using sediment class data are the new attempts made by the authors. Further this methodology aids in generating first generation sediment distribution maps.