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1.
Incorporating limited field operability and legacy soil samples in a hypercube sampling design for digital soil mapping 总被引：2，自引：0，他引：2 
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下载免费PDF全文 Felix Stumpf Karsten Schmidt Thorsten Behrens Sarah Schönbrodt‐Stitt Giovanni Buzzo Christian Dumperth Alexandre Wadoux Wei Xiang Thomas Scholten 《植物养料与土壤学杂志》2016,179(4):499-509
Most calibration sampling designs for Digital Soil Mapping (DSM) demarcate spatially distinct sample sites. In practical applications major challenges are often limited field accessibility and the question on how to integrate legacy soil samples to cope with usually scarce resources for field sampling and laboratory analysis. The study focuses on the development and application of an efficiency improved DSM sampling design that (1) applies an optimized sample set size, (2) compensates for limited field accessibility, and (3) enables the integration of legacy soil samples. The proposed sampling design represents a modification of conditioned Latin Hypercube Sampling (cLHS), which originally returns distinct sample sites to optimally cover a soil related covariate space and to preserve the correlation of the covariates in the sample set. The sample set size was determined by comparing multiple sample set sizes of original cLHS sets according to their representation of the covariate space. Limited field accessibility and the integration of legacy samples were incorporated by providing alternative sample sites to replace the original cLHS sites. We applied the modified cLHS design (cLHSadapt) in a small catchment (4.2 km2) in Central China to model topsoil sand fractions using Random Forest regression (RF). For evaluating the proposed approach, we compared cLHSadapt with the original cLHS design (cLHSorig). With an optimized sample set size n = 30, the results show a similar representation of the cLHS covariate space between cLHSadapt and cLHSorig, while the correlation between the covariates is preserved (r = 0.40 vs. r = 0.39). Furthermore, we doubled the sample set size of cLHSadapt by adding available legacy samples (cLHSadapt+) and compared the prediction accuracies. Based on an external validation set cLHSval (n = 20), the coefficient of determination (R2) of the cLHSadapt predictions range between 0.59 and 0.71 for topsoil sand fractions. The R2‐values of the RF predictions based on cLHSadapt+, using additional legacy samples, are marginally increased on average by 5%. 相似文献
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Stephen L. Rathbun 《Journal of Agricultural, Biological & Environmental Statistics》2006,11(3):317-336
Environmental monitoring of contaminants often involves left-censored observations falling below the minimum detection limits
(MDLs) of the instruments used to assay their concentrations. Statistical procedures for handling left-censored observations
generally assume that the observations are independently distributed. However, data collected over a spatial network of sample
sites are likely to be spatially correlated. This correlation structure can be exploited to obtain improved imputations of
left-censored observations, and hence improved estimates of environmental parameters. This article applies a Robbins-Monro
algorithm for estimating the parameters of a spatial regression model. This algorithm uses importance sampling to obtain conditional
simulations of left-censored observations. A predictor for data at unsampled sites is obtained by taking the weighted mean
of kriging predictors computed from independent importance samples. The proposed methods are illustrated using data from the
South Florida Ecosystem Assessment Project. 相似文献
4.
改进Niblack算法的光照不均匀QR码识别研究 总被引：1，自引：1，他引：0
QR码作为农产品可追溯体系的信息载体,一直是农业领域的科研热点。在实际应用中,溯源环境的复杂多变易使设备采集到光照不均匀的QR码图像而增加解码流程中二值化的难度,影响后续解码。该文针对原始Niblack算法自适应性不足的缺陷,提出一种自适应邻域窗口和修正系数的Niblack算法,该算法依据QR码图像的分辨率和灰度值,动态调整修正系数和邻域窗口,进行自适应二值化处理。分别用改进Niblack算法,原始Niblack算法和Otsu算法处理设备无法识别的不同光照环境下、不同程度的光照不均匀QR码图像,试验数据表明经改进算法处理后的识别成功率为74.2%,高出原始Niblack算法18.4%,高出Otsu算法71.7%,具有较高的鲁棒性。这一结果对农产品在各种光照不均匀环境中的溯源提供了参考。 相似文献
5.
空间自相关性对冬小麦种植面积空间抽样效率的影响 总被引：1，自引：1，他引：0
空间抽样是实现区域农作物面积高效估算的重要手段,农作物分布受自然条件等因素影响普遍存在空间自相关性,但以往针对空间相关性对农作物面积抽样效率的影响研究明显不足。该研究选取安徽省凤台县为研究区,通过2017年4月4景GF-1全色多光谱影像(Panchromatic and Multispectral, PMS)与Google Earth高空间分辨率影像相结合提取研究区冬小麦。设计10种抽样单元尺度、3种抽样外推方法、2种相对允许误差和5种样本布局方式,构建多种冬小麦面积空间抽样方案。利用全局莫兰指数(global Moran’s index)评价不种尺度下抽样单元内冬小麦面积比的空间自相关强度,分析空间自相关性对冬小麦面积抽样效率(抽样误差、样本容量和空间布局)的影响。研究结果表明,抽样单元内冬小麦面积比的空间自相关强度随单元尺度的增大而减小,全局莫兰指数相应地由0.75降至0.50。无论在何种尺度下抽样单元内冬小麦面积比都呈显著的空间正相关性;抽样外推冬小麦面积总体的误差随空间自相关强度的减小呈先减小后明显增大的趋势。在10种抽样单元尺度中,当抽样单元尺度为2000m且抽样比为5%时,无论采用何种抽样方法外推总体的误差均为最小(简单随机抽样、系统和分层抽样外推总体的相对误差分别为17.94%、9.48%和1.82%);当相对允许误差设计为5%时,简单随机抽样外推总体所需样本容量随空间自相关强度的降低从660降至56。而分层抽样的样本容量不受空间自相关性的影响;5种样本布局方式中,采用分层随机抽样方式外推冬小麦面积总体的平均相对误差、平均变异系数和均方根误差最小,分别为1.82%、3.19%和0.11×108 m2。该研究可为有空间自相关存在下的农作物面积空间抽样方案合理设计提供参考依据。 相似文献
6.
Sampling Designs for Validating Digital Soil Maps: A Review 总被引：1，自引：0，他引：1
Sampling design (SD) plays a crucial role in providing reliable input for digital soil mapping (DSM) and increasing its efficiency. Sampling design, with a predetermined sample size and consideration of budget and spatial variability, is a selection procedure for identifying a set of sample locations spread over a geographical space or with a good feature space coverage. A good feature space coverage ensures accurate estimation of regression parameters, while spatial coverage contributes to effective spatial interpolation. First, we review several statistical and geometric SDs that mainly optimize the sampling pattern in a geographical space and illustrate the strengths and weaknesses of these SDs by considering spatial coverage, simplicity, accuracy, and efficiency. Furthermore, Latin hypercube sampling, which obtains a full representation of multivariate distribution in geographical space, is described in detail for its development, improvement, and application. In addition, we discuss the fuzzy k-means sampling, response surface sampling, and Kennard-Stone sampling, which optimize sampling patterns in a feature space. We then discuss some practical applications that are mainly addressed by the conditioned Latin hypercube sampling with the flexibility and feasibility of adding multiple optimization criteria. We also discuss different methods of validation, an important stage of DSM, and conclude that an independent dataset selected from the probability sampling is superior for its free model assumptions. For future work, we recommend:1) exploring SDs with both good spatial coverage and feature space coverage; 2) uncovering the real impacts of an SD on the integral DSM procedure; and 3) testing the feasibility and contribution of SDs in three-dimensional (3D) DSM with variability for multiple layers. 相似文献
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A ranked set sample (RSS) is composed of independent order statistics, formed by collecting and ordering independent subsamples,
then measuring only one item from each subsample. If the cost of sampling is dominated by data measurement rather than collection
or ranking, the RSS technique is known to be superior to ordinary sampling. Experiments based on binary data are not designed
to exploit the advantages of ranked set sampling because categorical data typical are as easily measured as ranked, making
RSS methods impractical. However, in some environmental and biological studies, the success probability of a bivariate outcome
is related to one or more covariates. If the covariate information is not easily quantified, but can be objectively ordered
with respect to this success probability, the RSS method can be used to improve the analysis of binary data. This article
considers the case in which the covariate information is modeled in terms of a mixing distribution for the success probability,
and the expected success probability is of primary interest. The inference technique is demonstrated with water-quality data
from the Rappahannock river in Virginia. In a general setting, the RSS estimator is shown to be superior, including cases
in which error in judgment ranking is present. 相似文献
8.
《Communications in Soil Science and Plant Analysis》2012,43(21):2701-2717
ABSTRACTConventional sampling schemes for soil test guided nutrient management do not duly consider spatial variability. Fisher’s least significant difference (LSD) classical technique is sometimes manipulated for computing minimum sample size. However, it does not consider spatial dependence and relies on sample variance. Here, we present a new LSD-based robust method that uses semivariogram sill as a variance surrogate and then explore through sensitivity analysis novel alternative measurement units to reduce sample size rendered large by spatial variability. For differentiating crop response based categories, 273–22,320 samples were required for primary nutrients. Required sample size for detecting desired critical shifts in micronutrient status varied from 16–28,854. Changing to millimole units for potassium (K) and iron (Fe) further reduced sample size significantly. Thus, LSD-based technique can be made robust by using geostatistical techniques. Conventional measuring units in highly variable plant nutrients can be replaced with more practicable and economical units. 相似文献
9.
地面样本点是农作物遥感分类模型训练的基础，样本点数量和质量是影响模型分类精度的2个主要因素。该研究构建了数据驱动的样本点布设方法，利用待分类影像的光谱、植被指数等特征构造分层抽样底图，结合分层随机抽样方法进行地面样本点布设，并分析不同抽样策略对农作物遥感分类结果的影响。采取基于k-means聚类分析的数据驱动方法，考虑6景哨兵2号影像提取的共78个分类特征，生成同一个最优k的聚类结果图；设计等量分配和按面积比分配2种样本量分配方式，样本点数量为25、49、100、169、225的5个总样本量；基于不同抽样策略获取地面样本点信息，利用同一个支持向量机模型对待分类影像进行监督分类，并通过与139个样本点的理论总样本量和400个样本点的传统方式总样本量对比分析，定量解析不同抽样策略对分类精度的影响。结果表明：1）在数据驱动非监督聚类生成的底图上进行抽样（按面积比分层抽样法、等量分层抽样法）获得的样本点质量和分类精度明显优于没有该底图的抽样策略（简单随机抽样法、系统抽样法）；2）当总样本量低于理论总样本量时，等量分层抽样法能获取比按面积比分层抽样法更高的分类精度。例如，当理论样本量为139时，... 相似文献
10.
采样点数量对长三角典型地区土壤肥力指标空间变异解析的影响 总被引：9，自引：2，他引：7
通过对江苏省如皋市888个采样点的不重复随机抽样,探讨了采样点数量对土壤肥力指标空间变异解析的影响。从半方差函数估计的可靠性角度考虑,在长江冲积物形成的土壤上,针对县级农业管理和生态环境规划的土壤肥力指标调查采样,采集250个样点较为合适。另外,仅使用交互验证和独立验证评价半方差函数估计的可靠性及确定采样点数量是不完善的,而平均克里格方差理论上随采样点数量的增加而单调递减,可以作为不同采样点数量条件下,综合评价半方差函数估计可靠性及确定采样点数量的补充指标。 相似文献
11.
土壤制图中多等级代表性采样与分层随机采样的对比研究 总被引：6，自引：0，他引：6
采样设计是土壤地理研究中备受关注的重要问题。本文以区域尺度土壤属性制图为例,将多等级代表性采样与经典采样中的分层随机采样进行对比研究。以安徽宣城研究区的表层砂粒含量为目标要素,采集数量均为59个的两套样点,设计不同数量(46、58和59)的样点分组,采用两种制图方法进行制图并利用独立验证点进行评价。结果表明:1)无论是采用多元线性回归方法还是基于环境相似度的制图方法,在同等样点数量下,利用代表性样点所得土壤图精度均高于利用随机样点所得精度,并且利用少量代表性样点(46个)所得土壤图精度也高于利用多量随机样点(59个)所得精度;2)随着代表性较低样点的增加,土壤制图精度基本有一个提高的趋势,而采用随机样点所得土壤图的精度波动较大。因此,可认为多等级代表性采样方法是一种可用于区域尺度土壤调查的有效采样方法,且比分层随机采样高效、稳定。 相似文献
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Anne C. RICHER-de-FORGES Dominique ARROUAYS Laura POGGIO Songchao CHEN Marine LACOSTE Budiman MINASNY Zamir LIBOHOVA Pierre ROUDIER Vera L. MULDER Herv&#; N&#;D&#;LEC Guillaume MARTELET Blandine LEMERCIER Philippe LAGACHERIE Hocine BOURENNANE 《土壤圈》2023,33(5):731-743
Digital maps of soil properties are now widely available. End-users now can access several digital soil mapping (DSM) products of soil properties, produced using different models, calibration/training data, and covariates at various spatial scales from global to local. Therefore, there is an urgent need to provide easy-to-understand tools to communicate map uncertainty and help end-users assess the reliability of DSM products for use at local scales. In this study, we used a large amount of hand-feel soil texture (HFST) data to assess the performance of various published DSM products on the prediction of soil particle size distribution in Central France. We tested four DSM products for soil texture prediction developed at various scales (global, continental, national, and regional) by comparing their predictions with approximately 3 200 HFST observations realized on a 1:50 000 soil survey conducted after release of these DSM products. We used both visual comparisons and quantitative indicators to match the DSM predictions and HFST observations. The comparison between the low-cost HFST observations and DSM predictions clearly showed the applicability of various DSM products, with the prediction accuracy increasing from global to regional predictions. This simple evaluation can determine which products can be used at the local scale and if more accurate DSM products are required. 相似文献
13.
县域农田土壤采样布局多目标优化分析模型 总被引：2，自引：0，他引：2
合理布置农田土壤采样点可以在满足采样精度的前提下显著降低采样数量及成本,或在有限采样数量的限制下确保采样具有最佳的代表性。通过研究筛选区域范围内多种影响农田土壤养分采样点分布的因素,以及不同土壤养分的空间效应,建立区域农田土壤养分采样点布局多目标优化决策分析模型;并结合改进的遗传算法进行模型的求解过程分析。采用江苏省宝应县的农田空间数据及筛选的环境数据,分别从给定采样点数量条件下寻求最佳采样点分布方案,以及在满足采样精度和代表性的前提下确定最小采样点数量等2个角度进行了模型的分析验证工作;结果表明该模型可适用于解决县域范围大量分散耕作农田的土壤养分统一采样规划问题,为采样点的合理分布提供了一种定量优化分析手段。 相似文献
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15.
Clusters or groups of individuals are the fundamental unit of observation in many wildlife sampling problems, including aerial
surveys of waterfowl, marine mammals, and ungulates. Explicit accounting of cluster size in models for estimating abundance
is necessary because detection of individuals within clusters is not independent and detectability of clusters is likely to
increase with cluster size. This induces a cluster size bias in which the average cluster size in the sample is larger than
in the population at large. Thus, failure to account for the relationship between detectability and cluster size will tend
to yield a positive bias in estimates of abundance or density. I describe a hierarchical modeling framework for accounting
for cluster-size bias in animal sampling. The hierarchical model consists of models for the observation process conditional
on the cluster size distribution and the cluster size distribution conditional on the total number of clusters. Optionally,
a spatial model can be specified that describes variation in the total number of clusters per sample unit. Parameter estimation,
model selection, and criticism may be carried out using conventional likelihood-based methods. An extension of the model is
described for the situation where measurable covariates at the level of the sample unit are available. Several candidate models
within the proposed class are evaluated for aerial survey data on mallard ducks (Anas platyrhynchos). 相似文献
16.
Most soil sampling techniques are calibrated with standards and against each other, but the error introduced by the individuals performing each technique (sampler error) is often not addressed. We determined that sampler error explains a minimum of 5.5% of the variation in soil bulk density when using a composite coring technique. This source of error is of concern because it could easily obscure the small, but significant differences anticipated with long-term (decadal) research. We suggest three methods for increasing sampling accuracy across spatial and temporal treatments: (1) use > 5 individuals to sample each treatment; (2) consider both the concentration and pool size of soil properties (e.g. nitrate, root mass, etc.); and (3) include measurements of sampler error. 相似文献
17.
A sampling strategy is presented for soil survey in which an individual soil property is of interest and can be measured. It depends on first determining accurately the semi-variogram for the property, and this must be done in a prior reconnaissance stage of a survey. Then from the semi-variogram estimation variances can be found for any combination of block size and sampling density by the methods of kriging. Alternatively for a given block size the sampling density needed to achieve a predetermined precision (maximum estimation variance) can be determined. The strategy is optimal in the sense that the sampling effort is the least possible to achieve the precision desired. An equilateral triangular configuration of sampling points is best where variation is isotropic, but a square grid at the same density is very nearly as good, and will usually be preferred for convenience. Where there is simple anisotropic variation optimal sampling is achieved by choosing a rectangular grid with sides in the same proportion to one another as the slopes of the semi-variogram in the directions of maximum and minimum variation. 相似文献
18.
The principal component scoring: A new method of constituting a core collection using quantitative data 总被引：1，自引：0，他引：1
The principal aims of a core collection are: 1) to include the maximum of diversity of the base collection in a sample of minimum size; and 2) to avoid redundancies. We present here a new method (the Principal Component Scoring) which fulfills these aims. The use of P.C.S. has consequences for sampling stratification and choice of sample size. P.C.S. requires quantitative data, but with small changes can be used for qualitative data. 相似文献
19.
Determination of enantiomers of synthetic pyrethroids in water by solid phase microextraction - enantioselective gas chromatography 总被引：5，自引：0，他引：5
Solid phase microextraction (SPME) is an ideal sample preparation technique because of its speed and solvent-free features. Sampling by SPME is selective and only the dissolved concentration is measured, which allows measurement of the bioavailable fraction of a contaminant in aqueous media. One potential application of SPME is for analysis of enantiomers of chiral contaminants in environmental samples. In this study, a method was developed for determining enantiomers of (Z)-cis-bifenthrin and cis-permethrin in water using coupled SPME and enantioselective gas chromatography (GC). Following SPME sampling, enantiomers of (Z)-cis-bifenthrin and cis-permethrin were separated at the baseline on a beta-cyclodextrin-based enantioselective column, and analyte enrichment onto the SPME fiber was not enantioselective. The GC response increased as sampling time was increased from 0 to 240 min, and as sampling temperature was increased from 20 to 40 degrees C. Organic solvents such as methanol, acetone, and acetonitrile enhanced, while soil extracts slightly decreased, the GC response. The integrated SPME-enantioselective GC method was used to analyze surface runoff samples. The analysis showed preferential degradation of the 1S-3S enantiomer over the 1R-3R enantiomer for both (Z)-cis-bifenthrin and cis-permethrin. The concentrations detected by SPME-GC were substantially smaller than those determined following solvent extraction, suggesting that SPME-enantioselective GC analysis selectively measured the dissolved fraction. 相似文献
20.
土壤碱解氮空间变异与合理采样点数量研究 总被引：2，自引：0，他引：2
掌握土壤碱解氮变异特征是合理施肥与精准农业发展的前提,而合理采样点数量的确定是高效获取土壤碱解氮空间变异特征的基础。本研究基于江苏省沛县内约38 km2的区域中148个均匀分布的土壤采样点,分析了土壤碱解氮的空间变异特征,并通过区域随机抽样理论,计算了不同置信水平和误差等级的合理采样点数量。研究表明,沛县土壤碱解氮的平均含量为109.97 mg/kg,变异系数为0.29,其在空间分布上以中部和东南部局部地区土壤碱解氮含量较高,而东北部地区含量较缺乏;在95%置信水平上,当误差为5%和10%时的合理土壤采样点的数量分别为69个和27个;而在90%置信水平上,两误差等级所需合理采样点的数量分别为56个和20个。研究结果可为该地区土壤养分调查时高效采样方案的制定提供参考。 相似文献