All pixels are useful,but some are more useful: Efficient in situ data collection for crop-type mapping using sequential exploration methods

A precise knowledge of the crop distribution in the landscape is crucial for the agricultural sector to inform better management and logistics. Crop-type maps are often derived by the supervised classification of satellite imagery using machine learning models. The choice of data sampled during the data collection phase of building a classification model has a tremendous impact on a model's performance, and is usually collected via roadside surveys throughout the area of interest. However, the large spatial extent, and the varying accessibility to fields, often makes the acquisition of appropriate training data sets difficult. As such, in situ data are often collected on a best-effort basis, leading to inefficiencies, sub-optimal accuracies, and unnecessarily large sample sizes. This highlights the need for new more efficient tools to guide data collection. Here, we address three tasks that one commonly faces when planning to collect in situ data: which survey route to select among a set logistically feasible routes; which fields are the most relevant to collect along the chosen survey route; and how to best augment existing in situ data sets with additional observations. Our findings show that the normalised Moran's I index is a useful indicator for choosing the survey route, and that sequential exploration methods can identify the most important fields to survey on that route. The provided recommendations are flexible, overcome the main logistical constraints associated with in situ data collection, yield accurate results, and could be incorporated in a mobile application to assist data collection in real-time.     

On the Variability of the Fluxes of Momentum and Sensible Heat

Direct measurements of the air–sea turbulent fluxes of momentum and heat, along with surface currents, waves and supporting meteorological variables, were acquired during a recent field campaign. Surface currents, measured from a very high frequency radar, were found to steer the stress away from the mean wind direction. Although this effect has been reported in a recent scatterometer study, this is the first time it has been observed in an in situ study with co-located flux, wind and surface current measurements. Data collected during a week of stationary conditions are used to investigate and quantify the sampling variability of the air–sea fluxes of momentum and sensible heat.     

田间土壤含水率的空间结构及取样数目确定

本文以田间试验资料为基础,研究田间土壤含水率的空间变异性与空间结构。对1m土层不同深度的含水率与1m土层平均含水率作了统计、自相关与半方差分析,表明田间土壤存在着空间变异性。1m土层平均含水率的变差系数Cv小于各不同深度含水率的Cv值。资料还表明含水率在平面位置上相关性不显著。将田间含水率作为空间变异的随机变量,可计算其符合要求的置信水平P1和估值精度的合理取样数目。本文提供的取样数目表亦可供确定合理取样数目时参考。     

田块尺度作物辐射温度获取方法对比研究

热像仪的优势在于可以获得组分辐射温度,常用于地面温度同步测量实验中,其数据与植被覆盖度联合还可以得到作物田块尺度的平均辐射温度。以黑河流域进行的星—机—地遥感综合观测试验加密观测——盈科绿洲玉米地的热像仪和手持式红外辐射计温度测量数据为基础对不同采样方式获得的地面辐射温度进行对比。对于热像仪数据:①采用阈值法对热像仪影像中的玉米和土壤背景两组分进行分离,获得了各自辐射温度的平均值;②利用LAB彩色变换法处理同步拍摄的真彩色照片,获得每块玉米样地的植被覆盖度;③最终结合组分温度和植被覆盖度求得地块平均的辐射温度。经过实验对比发现,由热红外图像计算获得的地面平均辐射温度与手持式红外辐射计垂直垄或顺垄条带采样获得的地面平均辐射温度差值较小,基本在±1℃以内,而3种测量方式的最大值、最小值相差较多。还模拟了几种常见尺度下利用手持式红外辐射计进行随机采样时,其采样平均值以不同的置信度处于真实温度±0.5℃之间所对应的采样次数。分析表明,基于点测量的采样方案难以仅利用1~2台手持式红外辐射计实现对田块或更大尺度平均辐射温度的准确测量,高时空采样频率是保障地面辐射温度测量精度的前提,与遥感像元尺度相匹配的地面真实性检验需要...     

惰性气体同位素确定地热流体循环深度

地热系统惰性气体同位素地球化学是地热成因研究的重要手段。许多惰性气体同位素都可用于地热系统的研究中,主要目的为揭示热田的热源性质、深-浅层地热流体的内在联系和循环深度等。本文从惰性气体理化特点、样品采集、测试技术及数据等若干方面介绍了惰性气体研究方法,重点探讨了在自由气和溶解气两种形态下,热泉、喷气孔、热水井不同环境下的惰性气体采样方法,还介绍了成熟的惰性气体同位素的测试方法,即利用磁偏转静态真空质谱计分析测试方法,最后基于世界各地典型地热系统的惰性气体测试数据,讨论地热系统的气体来源判别,不同气源的混合比例计算等,进而确定地热流体循环深度。     

雨区衰减和雷达取样误差对713型双线偏振雷达测量精度的影响

为了确定713型双线偏振雷达的探测精度,本文利用电磁波的矩阵传播法计算了考虑椭球形雨滴在不同空间取向下,雨区衰减对713型双线偏振雷达的可测量反射率因子Z_H、差反射率因子Z_(DR)的影响。并利用已有的统计理论讨论了该雷达的取样误差,为实际雷达改装工作提供了依据。     

青藏高原科研文献地理信息空间分析研究

多学科的协同、渗透、交叉已成为当代科学发展的重要趋势,文献计量学和地理信息系统（GIS）技术的集成是拓展GIS应用领域的一个新兴方向。许多与地理空间位置有关的信息包含在大量地学科研文献中。从CNKI文献数据库收录的研究青藏高原的科研文献中提取研究区、样带和采样点等位置相关信息,运用GIS技术进行空间分析和展现。结果显示,青藏高原研究的主要学科领域集中在生态环境及其变化、地质与地球物理特征及其演化、资源及其勘探、地质工程等方面。有关青藏高原的研究在空间分布上存在较大的差异,对青藏高原的研究从西南、西北到东南、东北区域,其受关注的程度逐渐增加。祁连山脉、羌塘高原、青海湖、青藏公路、青藏铁路和川藏公路等是研究的热点区域。沿经度和纬度方向不同区间研究的分布也不同,研究热点区域呈现出从青藏高原中部向东北部转移的趋势。多数采样点和观测点沿交通干线分布,并且随着与交通干线距离的增加数量明显减少。GIS技术在关于青藏高原的文献计量分析中得到了有效应用,有助于挖掘出大量与空间位置相关的信息,从而深入分析青藏高原研究的发展态势。     

Total load transport in gravel bed and sand bed rivers case study:Chelichay watershed

Field experiments were conducted on total load transport in the Chelichay River Basin,a mountainous catchment (1,400 km~2) located in north eastern of Iran,to evaluate total load formulas including four gravel bed rivers and a sand bed river(Qaresoo River).Gravel bed rivers in Chelichay River Basin can be grouped into two types;steep slope rivers with high shear values(Chehelchay River and Khormaloo River) and mild slope rivers with low shear values(Narmab River and Soosara River).Two depth integrating suspended load samplers(DH-48 and D-49),and two bed load samplers(Helley-Smith and BLSH) were used to measure total load.The performance is tested of 8 total load transport formulae including 4 macroscopic and 4 microscopic methods.A systematic and thorough analysis of 59 sets of data collected from sand bed river indicate that Yang and Engelund and Hansen reach to the better results, and from four gravel bed rivers confirmed that the methods of Karim and Kennedy and Engelund and Hansen yields the best results for steep slope rivers,and the methods of Einstein and Bijker are ranked highest in gradual slope rivers.     

Effect of field plot location on estimating tropical forest above-ground biomass in Nepal using airborne laser scanning data

The prediction of tropical forest attributes using airborne laser scanning (ALS) is becoming attractive as an alternative to traditional field measurements. Area-based ALS inventories require a set of representative field plots from the study area, which may be difficult to obtain in tropical forests with limited accessibility. This study investigates the effect of sample-plot selection in Nepal, based on two accessibility factors: distance to road and degree of slope. The sparse Bayesian method was employed in the model to estimate above-ground biomass (AGB) with an independent validation dataset for model validation. Study findings showed that the sample plot distance and slope had a considerable effect on the accuracy of the AGB estimation, because the forest structure varied according to the level of accessibility. Thus, the field sample plots that are used in model construction should cover the full range of sample plot distances and slopes occurring within the area.     

ICP-AES在新疆哈拉奇地区水系沉积物样品分析中的应用研究

本文采用四酸溶样ICP6300电感耦合等离子体发射光谱法测试了新疆哈拉奇地区水系沉积物样品中的Li P Ti V Cr Mn Co Ni Cu Zn Sr Y Nb Mo Ba La Pb B W Sn Cd 21种微量元素,明确了该方法测试样品中的Li P Ti V Cr Mn Co Ni Cu Zn Sr Y Nb Mo Ba La 16个元素的检出限、准确度、精密度满足规范（DZ/T0130.2006-2006）要求,而Pb B Cd Sn W5个元素测试质量不能满足规范要求,并对新疆哈拉奇地区水系沉积物采样粒度样品进行了分析测试,验证了该区化探扫面选择10-80目粒度是合适的,但在异常查证工作中要选择10-60目采样粒度更合理。