稀疏格网样点的国家尺度土壤属性制图方法与应用

 国家尺度土壤属性数据是地球生物化学循环及水循环等领域研究的重要数据,目前,该尺度土壤属性数据的获取方法主要有两类:土壤属性-空间数据连接法和空间插值。为了确定哪一类方法更适合稀疏样点的国家尺度土壤属性制图,本文以中国吉林省的土壤有机质含量制图为例,采用8~32km格网样点和1∶100万土壤图,对这两类方法进行对比分析。独立样本验证结果表明,土壤属性-空间数据连接法的平均误差(ME)大于距离反比加权(IDW)插值,而平均绝对误差(MAE)和均方根误差(RMSE)都小于IDW插值。IDW插值获得的土壤属性图虽然能大致反映土壤属性空间分布的基本规律,但出现了类似"牛眼睛"的空间结构,且存在无样点区估计值不准确等问题;土壤属性-空间数据连接法尽管忽略了同种土壤类型内部的差异,保留了不同土壤类型边界处的属性值突变,但获得的土壤属性图更能反映土壤属性分布的基本规律,也具有比较详细的土壤属性空间结构。因此,在基于稀疏样点的国家尺度土壤属性制图中,土壤属性-空间数据连接法的制图效果要优于IDW空间插值法。

A Study on Soil Property Mapping at National Scale Based on Sparse Grid Soil Samples

Soil property data at national scale are necessary inputs for researches on biogeochemical and hydrological cycles.There are two commonly used methods to obtain accurate soil property data at this scale including soil linkage method and spatial interpolation method.In this paper,soil organic matter（SOM） content in Jilin Province was taken as a case study to evaluate these two methods based on 8～32 km grid soil samples and 1∶1 million soil map,in order to provide suggestions about soil property mapping at national scale based on sparse grid soil samples.Independent validation indicated that the mean error（ME） of the soil linkage method was-0.58,higher than the inverse distance weighted（IDW） interpolation method（0.13）,but the mean absolute error（MAE） and root mean square error（RMSE） of the soil linkage method were 1.12 and 1.76,respectively,lower than those of IDW interpolation method（1.43 and 2.12）.Although the soil property map through IDW interpolation revealed the general trend of soil property distribution,it had ＂Bull＇s eye＂ pattern and the estimations in areas with few or no soil samples were unreliable.The soil property map obtained by soil linkage method ignored the variations inside the same soil type on the soil map and a break of soil property existed around different soil boundaries,but the soil distribution regularity was well represented in this map and the details could be obtained.According to the validation results of maps through these two methods,the soil linkage method is better than the spatial interpolation method in soil property mapping based on sparse grid soil samples at national scale.