Evaluation of GIS Interpolation Techniques for Estimating the Radon Concentration for Unmeasured Zip Codes in the State of Ohio
Abstract (Summary)The main objective of this thesis is to predict the geometric mean of radon concentrations for unmeasured zip codes in the State of Ohio using the best geostatistical analyst interpolation technique. The radon concentration data used in this study spans from 1989-2005 (with some data sets obtained prior to 1989) and has been collected by the University of Toledo researchers from various commercial testing services, university researchers, and county health departments. This objective was achieved by first dividing the data into a 80% training data set and a 20% test data set and then applying five interpolation techniques on the training data set to evaluate the predictions for test data points. Several statistical indicators (root mean square error (RMSE), normalized mean square error (NMSE), fractional bias (FB), mean error (ME), mean absolute error (MAE), mean square error (MSE) and coefficient of correlation (r)) were computed on observed and predicted radon concentrations for evaluating the ability of predicting missing radon values using all interpolation techniques. The confidence limits on these indicators were obtained using the bootstrap resampling technique. The analysis of statistical indicators and confidence limits on the indicators clearly showed that none of the techniques is superior over the other. The spatial pattern of radon concentration generated using the measured values for all techniques were then compared with the uranium maps for the area. This exercise led to the exclusion of global and local polynomial interpolation technique. Assessment of the interpolation techniques using the soil uranium concentrations map showed that ordinary kriging interpolation technique can be used for predicting the radon concentrations for unmeasured zip codes. Radon concentration values for unmeasured zip codes were obtained and upon their examination, it was found that the number of zip codes having geometric mean of radon concentrations exceeding 4 pCi/l, 8 pCi/l and 20pCi/l were 688, 85 and 9 respectively.
School:University of Toledo
School Location:USA - Ohio
Source Type:Master's Thesis
Date of Publication:01/01/2007