整合已有土壤样点的数字土壤制图补样方案

An Integrative Sampling Scheme for Digital Soil Mapping

我国多数地区经过两次土壤普查以及科研工作者的野外调查,积累了一定数量的土壤样点"(已有样点")。本文在充分整合已有样点的基础上,提出了逐次、高效地设计补充样点的方案,它包括3个步骤:首先,确定已有样点集的空间代表范围"(可推测范围");然后,将已有样点集不能代表范围内的每一个栅格都看作一个候选样点,计算每一个候选样点的可扩推范围,选择可扩推范围最大的点作为第一个补充样点;最后,基于已有样点和补充样点更新样点集的空间代表范围图。重复以上过程,直至新样点集的空间代表范围能够覆盖整个研究区。该方法在充分利用已有样点资源的基础上,不仅能够确定补充样点的数量、位置,而且能够给定补充样点的重要性次序,在采样资源有限的情况下,为采样者合理地选择样点提供了重要依据。

In most areas there exist some soil field through two historical soil surveys and/or specific samples （＂existing samples data＂） which were accumulated field studies. The accuracy of soil property map predicted based on this kind of samples is lower, because the size of these samples is limited and the global representative- ness is poor. However, these samples are valuable resource because they do capture the relationship between soil and environment conditions. This paper presents a stepwise and effective method to design additional samples by integrating existing samples. The aim of the method is to design as few additional samples as possible to com- plement the global representativeness of the existing samples and improve the accuracy of predictive soil map- ping. The detail process is as follows. First, we determine the spatial extent which can be represented by the ex- isting samples. Second, each location （grid） can be considered as a candidate for additional sampling in the area which the existing samples do not cover and the area which can be covered by each candidate was then calculat- ed. Third, the location which can represent the largest additional area was chosen as the first additional sample. Finally, the above procedure was iterated until the new sample set covered the whole study area. This integrative sampling scheme can not only determine the number and the locations of additional samples, but also give the or- der of the samples. It provides samplers with the important information on how many points can be sampled reasonably when the available resources are limited.