US EPA

2565370 

Journal Article 

Architecture and Processes for National Ion Coverage Maps 

Vleeshouwer, J; Cresswell, RG; Stenson, M 

2009 

2007-2013 

WOS:000290045002009 

Salt accumulates on the land's surface via rainfall washout of dissolved ions and via dry deposition of salts attached to suspended dust particles. Local and regional studies, based on point data have provided an understanding of accession processes, but have not been compiled as a coherent spatial coverage for Australia, nor assessed in a temporal context, as is routinely carried out for northern America. This paper describes an information system which couples spatial analysis of salt accession modelling with GIS, to deliver national accession maps over the World Wide Web (WWW).



We illustrate this system through examination of chloride accession data across Australia. As ion accession is a spatially contiguous process, it is important to place the site-specific information into a surface Expanding from a point-based representation to a surface provides a richer means of visualisation, and hence analysis, of the geographic variation of chloride.



The key components of this system (Figure 1) are: a relational database to store site observations for modelling; the modelling application; a geospatial database to store spatial layers; and a web map application for visualisation.



We use an empirical model to estimate the deposition of chloride (kg/ha) across Australia. This follows previous research which related chloride accession to rainfall, wind direction and distance from the coast. The model was developed using The Invisible Modelling Environment (TIME) in the C#.NET programming language. It also exploits the Surfer application to assist with interpolation of site observations from the relational database.



To account for the natural variability of the atmosphere, Australia was subdivided into Uniform Geographical Units (UGUs) characterised by Australia's climatic zones. Grid cells within each UGU were parameterised based on chloride concentrations measured in rainfall at sites within each UGU. A base chloride accession map was generated from the aggregate of similar to 200 chloride observations across Australia. The approach was tested by comparing observed values to the modelled base accession map. Correlation gave an r(2) of 0.72.



Chloride accession grids were stored within an ESRI geospatial database. The OpenGIS Web Map Service (WMS) standard was used to request the geo-referenced maps from the database, allowing them to be delivered over the internet to WMS compatible clients. An interactive web map application was developed using ArcGIS Server to view the maps via a WWW browser.



Ongoing work focuses on extending the system to produce temporal chloride accession coverage maps. This spatio-temporal data will provide a mechanism to produce coverage animations, based on the on-going collection of point-based accession data. Emphasis will be placed on the automatic generation of these maps on a regular basis. 

Relational database; Salt accession; GIS web delivery; Regression analysis; Maps