Uphill or downhill?Cropland use change and its drivers from the perspective of slope spectrum

The continuous decrease of low-slope cropland resources caused by construction land crowding poses huge threat to regional sustainable development and food security.Slope spectrum analysis of topographic and geomorphic features is considered as a digital terrain analysis method which reflects the macro-topographic features by using micro-topographic factors.However,pieces of studies have extended the concept of slope spectrum in the field of geoscience to construction land to explore its expansion law,while research on the slope trend of cropland from that perspective remains rare.To address the gap,in virtue of spatial analysis and geographically weighted regression(GWR)model,the cropland use change in the Yangtze River Basin(YRB)from 2000 to 2020 was analyzed and the driving factors were explored from the perspective of slope spectrum.Results showed that the slope spectrum curves of cropland area-frequency in the YRB showed a first upward then a downward trend.The change curve of the slope spectrum of cropland in each province(municipality)exhibited various distribution patterns.Quantitative analysis of morphological parameters of cropland slope spectrum revealed that the further down the YRB,the stronger the flattening characteristics,the more obvious the concentration.The province experienced the greatest downhill cropland climbing(CLC)was Shannxi,while province experienced the highest uphill CLC was Zhejiang.The most common cropland use change type in the YRB was horizontal expansion type.The factors affecting average cropland climbing index(ACCI)were quite stable in different periods,while population density(POP)changed from negative to positive during the study period.This research is of practical significance for the rational utilization of cropland at the watershed scale.

Slope spectrum critical area and its spatial variation in the Loess Plateau of China

Slope spectrum has been proved to be a significant methodology in revealing geomorphological features in the study of Chinese loess terrain. The determination of critical areas in deriving slope spectra is an indispensable task. Along with the increase in the size of the study area, the derived spectra are becoming more and more alike, such that their dif- ferences can be ignored in favor of a standard. Subsequently, the test size is defined as the Slope Spectrum Critical Area （SSCA）. SSCA is not only the foundation of the slope spectrum calculation but also, to some extent, a reflection of geomorphological development of loess relief. High resolution DEMs are important in extracting the slope spectrum. A set of 48 DEMs with different landform areas of the Loess Plateau in northern Shaanxi province was selected for the experiment. The spatial distribution of SSCA is investigated with a geo-statistical analysis method, resulting in values ranging from 6.18 km^2 to 35.1 km^2. Primary experimental results show that the spatial distribution of SSCA is correlated with the spatial distribution of the soil erosion intensity, to a certain extent reflecting the terrain complexity. The critical area of the slope spectrum presents a spatial variation trend of weak-strong-weak from north to south. Four terrain parameters, gully density, slope skewness, terrain driving force （Td） and slope of slope （SOS）, were chosen as indicators. There exists a good exponential function relationship between SSCA and gully density, terrain driving force （Td） and SOS and a loga- rithmic function relationship between SSCA and slope skewness. Slope skewness increases, and gully density, terrain driving force and SOS decrease with increasing SSCA. SSCA can be utilized as a discriminating factor to identify loess landforms, in that spatial distributions of SSCA and the evolution of loess landforms are correlative. Following the evolution of a loess landform from tableland to gully-hilly region, this also proves that SSCA can represent the development degree of local landforms. The critical stable regions of the Loess Plateau represent the degree of development of loess landforms. Its chief significance is that the per- ception of stable areas can be used to determine the minimal geographical unit.

Slope spectrum variation in a simulated loess watershed

A simulated loess watershed, where the loess material and relief properly represent the true loess surface, is adopted to investigate the variation in slope spectrum with loess watershed evolution. The evolution of the simulated loess watershed was driven by the exogenetic force of artificial rainfall. For a period of three months, twenty artificial rainfall events with different intensities and durations were carried out. In the process, nine DEM data sets, each with 10mm grid resolution, were established by the method of close-range photogrammetry. The slope spectra were then extracted from these DEMs. Subsequent series of carefully designed quantitative analyses indicated a strong relationship between the slope spectrum and the evolution of the simulated loess watershed. Quantitative indices of the slope spectrum varied regularly following the evolution of the simulated loess watershed. Mean slope, slope spectrum information entropy （H）, terrain driving force （Td）, Mean patch area （AREA_MN）, Contagion Index （CONTAG）, and Patch Cohesion Index （COHESION） kept increasing following the evolution of the simulated watershed, while skewness （S）, Perimeter-Area Fractal Dimension （PAFRAC）, and Interspersion and Juxtaposition Index （IJl） represented an opposite trend. All the indices changed actively in the early and active development periods, but slowly in the stable development periods. These experimental results indicate that the time series of slope spectra was able to effectively depict the slope distribution of the simulated loess watershed, thus presenting a potential method for model- ing loess landforms.

Research on the slope spectrum of the Loess Plateau

A new concept dealing with digital analysis of loess terrain,slope spectrum,is presented and discussed in this paper,by introducing its characteristic,represen-tation and extracting method from DEMs. Using 48 geomorphological units in dif-ferent parts of the loess as test areas and 5 m-resolution DEMs as original test data,the quantitative depiction and spatial distribution of slope spectrum in China's Loess Plateau have been studied on the basis of a series of carefully-designed experiments. In addition,initial experiment indicates a strong relationship between the slope spectrum and the loess landform types,displaying a potential importance of the slope spectrum in geomorphological studies. Based on the slope spectrums derived from the 25 m-resolution DEM data in whole loess terrain in northern part of Shaanxi,13 slope spectrum indices were extracted and integrated into a compre-hensive layer with image integration method. Based on that,a series of unsuper-vised classifications was applied in order to make a landform classification in northern Shaanxi Loess Plateau. Experimental results show that the slope spec-trum analysis is an effective method in revealing the macro landform features. A continuous change of slope spectrum from south to north in northern Shaanxi Loess Plateau shows an obvious spatial distribution of different loess landforms. This also proves the great significance of the slope spectrum method in describing the terrain roughness and landform evolution as well as a further understanding on landform genesis and spatial distribution rule of different landforms in the Loess Plateau.

Slope wavenumber spectrum models of capillary and capillary-gravity waves

Capillary and capillary-gravity waves possess a random character, and the slope wavenumber spectra of them can be used to represent mean distributions of wave energy with respect to spatial scale of variability. But simple and practical models of the slope wavenumber spectra have not been put forward so far. In this article, we address the accurate definition of the slope wavenumber spectra of water surface capillary and capillary-gravity waves. By combining the existing slope wavenumber models and using the dispersion relation of water surface waves, we derive the slope wavenumber spectrum models of capillary and capillary-gravity waves. Simultaneously, by using the slope wavenumber models, the dependence of the slope wavenumber spectrum on wind speed is analyzed using data obtained in an experiment which was performed in a laboratory wind wave tank. Generally speaking, the slope wavenumber spectra are influenced profoundly by the wind speed above water surface. The slope wavenumber spectrum increases with wind speed obviously and do not cross each other for different wind speeds. But, for the same wind speed, the slope wavenumber spectra are essentially identical, even though the capillary and capillary-gravity waves are excited at different times and locations. Furthermore, the slope wavenumber spectra obtained from the models agree quite well with experimental results as regards both the values and the shape of the curve.

Deriving the slope-mean shielded astronomical solar radiation spectrum and slope-mean possible sunshine duration spectrum over the Loess Plateau

Solar radiation is often shielded by terrain relief, especially in mountainous areas, before reaching the surface of the Earth. The objective of this paper is to study the spatial structures of the shielded astronomical solar radiation(SASR) and the possible sunshine duration(PSD) over the Loess Plateau. To this end, we chose six test areas representing different landforms over the Loess Plateau and the software package of Matlab was used as the main computing platform. In each test area, 5-m-resolution digital elevation model established from 1:10,000 scale topographic maps was used to compute the corresponding slope, SASR and PSD. Then, we defined the concepts of the slope-mean SASR spectrum and the slope-mean PSD spectrum, and proposed a method to extract them from the computed slope, SASR and PSD over rectangular analysis windows. Using this method, we found both spectrums in a year or in a season for each of the four seasons in the six test areas. Each spectrum was found only when the area of the corresponding rectangular analysis window was greater than the corresponding stable area of the spectrum. The values of the two spectrums decreased when the slope increased.Furthermore, the values of the stable areas of the spectrums in a year or in a season were positively correlated with the variable coefficients of the slope or the profile curvature. The values of the stable areas of the two spectrums in a year or in a season may represent the minimum value of test areas for corresponding future research on the spatial structures of the SASR or PSD. All the findings herein suggest that the spatial structures of the PSD and the SASR are caused by the interactions between solar radiation and terrain relief and that the method for extracting either spectrum is effective for detecting their spatial structures. This study may deepen our understanding of the spatial structure of solar radiation and help us further explore the distribution of solar energy in mountainous regions.

坡谱信息熵与区域水土流失关系研究

坡谱信息熵可以在宏观上反映地形起伏特征和地貌组合差异,且计算相对便捷。为探索坡谱信息熵与区域水土流失之间的关系,文章以西北黄土高原水土保持区为例,基于ALOS数字高程模型(空间分辨率12.5 m)计算研究区内的坡谱信息熵、土壤侵蚀模数,构建坡谱信息熵与土壤侵蚀模数之间的函数关系。研究结果表明:研究区内坡谱曲线主要为“L”形、“S”形,坡谱信息熵值在0.67~1.72nat之间;平均土壤侵蚀模数为1940t/(km^(2)·a)。在流域尺度、二级尺度和三级尺度上,构建坡谱信息熵与土壤侵蚀模数的函数模型,均呈极显著的多项式函数关系,但在流域尺度上,坡谱信息熵与土壤侵蚀模数的关系存在较大不确定性。

基于卫星海面高度资料的太平洋海区涡旋能谱分析

在空间均匀和各向同性的假定下,地转湍流理论认为涡旋动能随尺度分布遵循k–n定律(k为波数)。但实际海洋受边界、地形、层结等,具有明显的非均匀、各向异性特征。鉴于此,我们基于近30a卫星高度计资料,分别计算了热带、副热带、中高纬度等海洋涡旋强度不同区域的海面高度异常(SSHA)波数谱,进而利用线性回归拟合方法估算出中尺度波段上SSHA波数谱的斜率,并与地转湍流理论预测进行了对比。研究结果显示:SSHA波数谱从赤道到中高纬度逐渐变陡,其斜率由–4减到–5,基本符合赤道线性波动理论和准地转湍流理论的预测。SSHA波数谱斜率存在纬向与经向差异,例如在赤道地区,纬向谱比相应的经向谱陡;而在南极绕极流区域,经向谱斜率大于纬向谱斜率。SSHA波数谱斜率的各向异性表明海洋中尺度运动受β效应影响,具有明显的经向和纬向差异。以上结果表明,海洋中尺度运动介于准二维和三维之间,不能用一个全球普适的湍流理论模型来描述。

基于双能量CT中双能量指数、原子序数结合能谱曲线斜率对于鉴别泌尿系结石成分的价值研究

目的:评估双能量计算机体层扫描(DECT)的双能量指数(DEI)、有效原子序数(Zeff)结合能谱曲线斜率在鉴别患者泌尿系结石成分的价值。方法:收集2019年10月至2022年10月在南通市海门区人民医院就诊的111例泌尿系结石患者的临床及DECT影像资料。所有患者泌尿系结石直径均>5 mm,所有患者的离体结石均经红外光谱分析确定结石成分。分别计算DEI、Zeff、能谱曲线斜率及三者结合对于鉴别泌尿系结石成分的准确率、灵敏度、特异度等。结果:111例患者中草酸钙结石75例(占67.57%),羟基磷灰石15例(占13.51%),尿酸结石21例(占18.92%),未发现胱氨酸等其他类型结石。3种类型结石的CT值(F=487.691,P<0.001)、DEI(F=395.553,P<0.001)、Zeff(F=818.689,P<0.001)和能谱曲线斜率(H=19.615,P<0.001)比较的差异均有统计学意义。DEI、Zeff和能谱曲线斜率对鉴别泌尿系结石成分的总准确率分别为87.39%(97/111)、84.68%(94/111)和81.98%(91/111)。DEI、Zeff和能谱曲线分别对草酸钙结石、羟基磷灰石及尿酸结石诊断准确率均为80%~100%。DEI、Zeff结合能谱曲线斜率对鉴别泌尿系结石成分的总准确率为94.59%(105/111)。DEI、Zeff结合能谱曲线斜率对草酸钙结石、羟基磷灰石及尿酸结石诊断的准确性分别为94.59%、94.59%和100%。结论:与DECT的单个指标相比,DEI、Zeff结合能谱曲线斜率对鉴别泌尿系结石成分显示出更好的诊断准确率。

Dynamic failure mode and energy-based identification method for a counter-bedding rock slope with weak intercalated layers

The dynamic failure mode and energybased identification method for a counter-bedding rock slope with weak intercalated layers are discussed in this paper using large scale shaking table test and the Hilbert-Huang Transform(HHT) marginal spectrum.The results show that variations in the peak values of marginal spectra can clearly indicate the process of dynamic damage development inside the model slope.The identification results of marginal spectra closely coincide with the monitoring results of slope face displacement in the test.When subjected to the earthquake excitation with 0.1 g and 0.2 g amplitudes,no seismic damage is observed in the model slope,while the peak values of marginal spectra increase linearly with increasing slope height.In the case of 0.3 g seismic excitation,dynamic damage occurs near the slope crest and some rock blocks fall off the slope crest.When the seismic excitation reaches 0.4 g,the dynamic damage inside the model slope extends to the part with relative height of 0.295-0.6,and minor horizontal cracks occur in the middle part of the model slope.When the seismic excitation reaches 0.6 g,the damage further extends to the slope toe,and the damage inside the model slope extends to the part with relative height below 0.295,and the upper part(near the relative height of 0.8) slides outwards.Longitudinal fissures appear in the slope face,which connect with horizontal cracks,the weak intercalated layers at middle slope height are extruded out and the slope crest breaks up.The marginal spectrum identification results demonstrate that the dynamic damage near the slope face is minor as compared with that inside the model slope.The dynamic failure mode of counter-bedding rock slope with weak intercalated layers is extrusion and sliding at the middle rock strata.The research results of this paper are meaningful for the further understanding of the dynamic failure mode of counter-bedding rock slope with weak intercalated layers.

Measurements of ocean wave spectrum from airborne radar at small incidence angles

This paper proposes the retrieval method of ocean wave spectrum for airborne radar observations at small incidence angles, which is slightly modified from the method developed by Hauser. Firstly, it makes use of integration method to estimate total mean square slope instead of fitting method, which aims to reduce the affects of fluctuations superposed on normalized radar cross-section by integration. Secondly, for eliminating the noise spectrum contained in signal spectrum, the method considers the signal spectrum in certain look direction without any long wave components as the assumed noise spectrum, which would be subtracted from signal spectrum in any look direction for linear wave spectrum retrieval. Estimated v from the integration method are lower than the one from fitting method and have a standard deviation of 0.004 between them approximately. The assumed noise spectrum energy almost has no big variations along with the wave number and is slightly lower to the high wave number part of signal spectrum in any look direction, which follows that the assumption makes sense. The retrieved directional spectra are compared with the buoy records in terms of peak wavelength, peak direction and the significant wave height. Comparisons show that the retrieved peak wavelength and significant wave height are slightly higher than the buoy records but don＇t differs significantly （error less than 10%）. For peak direction, the swell waves in first case basically propagate in the wind direction 6 hours ago and the wind-generated waves in second case also propagate in the wind direction, but the 180° ambiguity remains. Results show that the modified method can carry out the retrieval of directional wave spectrum.

Wave Reflection Coefficient Spectrum

The wave reflection coefficient frequency spectrum and directional spectrum for concrete face slope breakwaters and rubble mound breakwaters are investigated through physical model tests in the present study. The reflection coefficients of oblique irregular waves are analyzed by the Modified Two-Point Method (MTPM) proposed by the authors. The results show that the wave reflection coefficient decreases with increasing wave frequency and incident angle or decreasing structure slope. The reflection coefficient frequency spectrum and its variation with Iribarren number are given in this paper. The paper also suggests an empirical 3-dimensional reflection coefficient spectrum, i.e. reflection coefficient directional spectrum, which can be used to illustrate quantitatively the variation of reflection coefficient with the incident angle and the Iribarren number for oblique irregular waves.

Transformation and Breaking of Irregular Waves on Very Gentle Slopes

Based on theoretical analysis, numerical calculation, and experimental study. this paper discusses breaker indices of irregular waves, transformation of wave spectrum, characteristics and computation of breaking waves, as well as the critical beach slope under which waves will not break. Computed results are in good agreement with laboratory physical model test data and ocean wave field measurements.

南海岛礁泻湖区域波浪双峰谱的特征研究

当波浪从深水区传播到岛礁的浅水区域时,由于珊瑚礁复杂的地形地貌,其波浪谱特征与深海中的波浪谱特征会有较大差异。根据南海西沙环礁泻湖内原位测点的波浪谱实测数据,双峰谱发生概率较大。本文首先分析了夏季台风浪和冬季东北季风浪两种典型海况下平衡范围内双峰谱的斜率,发现其斜率值与深海区有较大差异,进而得到低频峰值频率和高频峰值频率的特征值分布范围。然后基于以上分析,采用基于Ochi-Hubble谱型重构泻湖内的双峰波浪谱,得到混合波浪中风浪分量和涌浪分量的参数表达式,较好地描述了岛礁海域双峰波浪谱的特征。本文的研究成果可为近岛礁工程和海洋工程的结构物设计制造提供参考。

2000—2020年湖南省耕地坡谱演变规律研究

耕地是粮食生产的根基。文章利用土地利用数据和数字高程数据,结合坡谱分析方法,构建了耕地上山指数,分析了2000—2020年耕地坡谱在省和区域2个尺度上的变化规律以及影响耕地坡度变化的因素。结果显示:(1)2000—2020年时间段内,湖南省耕地的平均坡度增加了0.09°,高坡度(10°以上)地区耕地面积比例增加了0.68%,湖南省耕地逐渐向高坡度地区发展。(2)在区域尺度,经济相对发达的长株潭地区和地形较复杂的大湘西地区,耕地上山现象明显;经济较发达、以平原为主的洞庭湖地区,耕地上山现象不明显;湘南地区受到地形限制和经济快速发展双重影响,耕地上山程度仅次于长株潭地区。(3)退耕还林、非农建设、土地综合整治是影响耕地坡度变化的主要因素,可通过积极稳妥开展退耕还林工作、合理引导建设用地上山、严控新增耕地管理等措施,来减缓耕地在高坡度区域增加趋势,即减缓耕地上山现象。

Slope Year for the U-Pb Dating Method and Its Applications

The slope year tslope for the U-Pb dating method is given as , where λ238 and λ235 are the decay constants for 238U and 235U, respectively, and k is the slope of the tangent line at a point on either the Concordia or Discordia line. These two lines are determined by the initial 206(7)Pbi concentrations in minerals. If , the line is the Concordia. However, if (∧?is the logical operator “and”, also known as the logical conjunction), or , the line is Discordia. The Concordia line is of the form (where p stands for the present), while the Discordia line has the form (where k and b are the slope and intercept of the straight line, respectively).

灰岩崩塌体斜坡动力响应与损伤识别

灰岩崩塌体斜坡在天然状态下的稳定性较高,但剧烈地震作用会造成岩体裂缝扩展,导致斜坡发生破坏。通过大型振动台模型试验,研究强震条件下灰岩崩塌体斜坡的动力响应、破坏模式以及能量传递规律。结果表明:地震作用下灰岩崩塌体斜坡的破坏过程主要分为坡肩节理受拉开裂及顶部岩层剪切错动、垂直节理裂缝扩展及剪切位移增加、阶梯状贯通滑动面形成和岩体失稳滑塌4个阶段,破坏模式符合拉裂-剪切-滑移型破坏;斜坡的加速度响应表现出高程放大效应和趋表效应,0.55倍坡高以下时PGA放大系数近似呈线性增长,而在0.55倍坡高以上时PGA放大系数增长较为迅速;当输入地震波幅值小于0.4g时,PGA放大系数随输入波幅值增加而增加,当幅值超过0.4g后,PGA放大系数会有所降低;边际谱识别显示,边坡损伤在从坡肩位置开始,逐渐向下转移,且坡表损伤程度大于坡体内部;在进行损伤判识时,边际谱的灵敏度要优于PGA放大系数。

基于斜坡法的智能化架空线路应变快速感知

为了提高输电线路状态感知实时性,将单斜坡法和基于伪Voigt模型的最小二乘谱拟合法用于架空线路复合光纤应变的测量,基于实测布里渊谱系统,研究了工作点增益的信噪比和布里渊频移对单斜坡法准确性的影响。结果表明,随着工作点增益信噪比增加,布里渊频移误差近似成指数规律减小;随着布里渊频移与工作点频率之差的增加,布里渊频移误差先快速下降,然后略有增加;当工作点处布里渊增益的信噪比不小于25 dB且工作点频率始终小于(或大于)布里渊频移时,单斜坡法应变误差小于60με;根据不同布里渊频移下60με对应的临界信噪比,可插值获得不同情况下对应的临界信噪比;单斜坡法的谱测量时间和计算时间分别为谱拟合法的1/161和1/600左右。该工作为提高智能化光纤复合架空线路态势感知实时性奠定了基础。

基于自适应波谱斜率的海面风速反演算法研究

对于波浪谱风速反演研究,虽然已经建立了波谱平衡范围斜率为-4幂律的初步反演模型,然而对于复杂多变的实测波谱,单一斜率模型的反演效果不佳。针对可变波谱斜率的问题,通过量化波谱函数对应的谱系数,提出一种自适应波谱斜率的风速反演算法。为了验证该算法估算风的准确性,本文通过对NDBC浮标观测的大量风浪数据进行海面风速反演研究,结果显示自适应波谱斜率算法反演风速与实测风速相关系数R=0.83,呈显著相关,且平均偏差BIAS和均方根误差RMSE分别为0.75 m/s和2.48 m/s。通过近海海试实验验证表明该算法依然有效具有普适性。总的来看,自适应波谱斜率反演风速算法与实测风速之间误差相对较小,反演精度较好,为风浪观测和风浪研究提供了一种新思路,且该算法能够融合应用于海洋观测应用平台,使理论研究和工程实际相结合。

基于小波包和反应谱的黄土边坡动力特征研究

为研究黄土边坡在地震动力作用下的动力响应特征,以宝兰客专沿线某天然黄土边坡为工程背景,建立1∶20缩尺的黄土边坡试验模型。通过大型振动台试验,采用时程分析和小波包、反应谱分析相结合的方法,在模型底部振动台上输入地震动荷载,分析黄土边坡结构在地震动荷载下加速度信号第一频段能量占比(E_(1))、第二频段能量占比(E_(2))、特征周期、反应谱幅值、峰值加速度(PGA)和加速度放大系数(AFA)的变化规律。结果表明:根据E_(1)、E_(2)转化规律,弹性阶段可以细分为挤压密实阶段和密实阶段,E_(1)+E_(2)的最大值位于边坡顶部位置。在弹塑性阶段,同种类型地震波不同地震烈度下到达特征周期的时间基本不变,El-Centro波到达特征周期的时间滞后于汶川汤峪波,且其加速度、速度反应谱幅值也略小。模型在水平方向上存在PGA及AFA放大效应,PGA及AFA沿水平方向放大效应按照大小排序为:破坏阶段>塑性阶段>弹性阶段。地震过程中距离坡面越近的位置越容易被破坏和先破坏,验证了地震过程中“鞭梢效应”的存在。