基于球坐标转换的土壤机械组成空间插值研究

Spatial Interpolation of Soil Mechanical Composition Based on Spherical Coordinate Transform Method

土壤机械组成作为一种成分数据,为满足其空间插值的定额、非负、线性无偏和最优要求,通常需要对其进行转换。本文以宁夏银北地区土壤机械组成数据为例,引进了球坐标转换方法,利用经球坐标转换、对称对数比转换和非对称对数比转换后的数据进行普通克里格插值,分析了球坐标转换方法对土壤机械组成数据转换的可行性与科学性,并比较了不同转换方法对土壤机械组成空间预测效果的影响。结果表明:球坐标转换方法能满足土壤机械组成空间插值要求,对于研究区砂粒、粉粒的空间插值精度较对称对数比转换和非对称对数比转换方法高,而对于黏粒,其插值精度却逊于对称对数比转换和非对称对数比转换方法。本研究为土壤机械组成空间插值提供了一种易于理解、计算量小、不需要考虑零值、又能保证一定插值精度的转换方法。

As a kind of compositional data,the spatial interpolation of soil mechanical composition needs to meet four constraints of constant sum, nonnegativity, linear unbiased estimation and error minimization. Therefore, it usually needs to be transformed before spatial interpolation. A novel transformation method-spherical coordinate transform method was proposed and the study area was located in Yinbei Irrigation District,Ningxia Hui Autonomous Region. Firstly,the sampled soil mechanical composition data was transformed through three methods,including symmetry logratio transform method,asymmetry logratio transform method and the proposed spherical coordinate transform method,respectively. Then the soil mechanical composition spatial interpolation was realized with the application of ordinary Kriging. Secondly,the soil mechanical composition interpolation maps of different transform methods were compared to analyze the scientificity and feasibility of the proposed transform approach. The precision and fitting effect were assessed by utilizing the mean absolute error（ MAE）,root mean square error（ RMSE）,index of agreement（ d） and Pearson＇s correlation（ R）. The results indicated that spherical coordinate transform technology not only can satisfy the four constraint conditions but also had superior interpolation accuracy for sand and silt content than the other two logratio transform methods.However,the logratio transform methods had more accurate interpolation results than spherical coordinate transform method for clay content prediction. To summarize,a novel transform technology with the advantages of easy understanding,small calculation amount,and good interpolation precision and without consideration of zero values for spatial interpolation of soil mechanical composition was presented.