| Volumes and Issues Contents of Issue 7 Special Issue |
www.biogeosciences.net/7/2081/2010/
doi:10.5194/bg-7-2081-2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
A linear mixed model, with non-stationary mean and covariance, for soil potassium based on gamma radiometry
1Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK
2British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK
Abstract. In this paper we present a linear mixed model for the potassium content of soil across a large region of eastern England in which the mean is modelled as a linear function of the passive gamma-ray emissions of the earth surface in the energy interval commonly associated with potassium decay. Non-stationary models are proposed for the random effect, which is the variation not captured by this regression. Specifically, we assume that the local spectrum of the standardized random effect can be obtained by tempering a common (stationary) spectrum, that is to say raising its values to a power, the tempering parameter, which is itself modelled as a linear function of the radiometric data. This allows the "smoothness" of the random effect to vary locally. In addition the local spatially correlated variance and "nugget" variance (apparently uncorrelated given the resolution of the sampling) can also be modelled as a function of the radiometric data. Using the radiometric signal as a covariate gave some improvement in the precision of predictions of soil potassium at validation sites. In addition, there was evidence that non-stationary models for the random effect fitted the data better than stationary models, and this difference was statistically significant. Non-stationary models also appeared to describe the error variance of predictions at the validation sites better. Further work is needed on selection among alternative non-stationary models, since simple procedures used here, based on comparing log-likelihood ratios of nested models and the Akaike information criterion for non-nested models, did not identify the model which gave the best account of the prediction error variances at validation sites.
Final Revised Paper (PDF, 548 KB) Discussion Paper (BGD) Special Issue
Citation: Haskard, K. A., Rawlins, B. G., and Lark, R. M.: A linear mixed model, with non-stationary mean and covariance, for soil potassium based on gamma radiometry, Biogeosciences, 7, 2081-2089, doi:10.5194/bg-7-2081-2010, 2010. Bibtex EndNote Reference Manager XML
Search BG
News
- Impact factor for 2010 confirms the prominent position of Biogeosciences
- Overview of Scheduled Special Issues
- Three times in 2010, Biogeosciences has achieved the highest percent increase in total citations among journals in the field of Environment & Ecology in Essential Science IndicatorsSM from Thomson Reuters. For more information see: http://sciencewatch.com.
- EGU Position Statement on Discussion Papers