Thermal Anomalies and Earthquakes： Evidence from Wenchuan, China

Earthquake prediction is a difficult problem in Earth sciences.Unsuccessful predictions one after another urged people to explore more synthetic and comprehensive methods for earthquake prediction.The Lithosphere-Atmosphere-Ionosphere(LAI)coupling theory pays great attention to the processes taking place within the near ground layer of atmosphere.It has achieved great results recently,and can enlighten us about the nature of an earthquake's precursor.Based on the NCEP reanalysis dataset,this paper attempts to track the anomalies of the surface's upward long wave radiation flux(ULWRF),the temperature at the depth of 10cm～20cm below ground surface layer(BGL)and the air temperature at 2 meters above ground surface(AIR)around the time of the strong Wenchuan earthquake.Thermal anomalies were observed before and after May 12,2008,the time of the Wenchuan earthquake.Perhaps the thermal anomaly that occurred prior to the earthquake can be taken as indicators of the earthquake,but in view of the complexity of the earthquake phenomena,using thermal anomaly as a precursor should be done with caution.     

利用DEMETER卫星数据分析汶川地震前的电离层异常

DEMETER卫星由法国于2004年6月发射,高度约为665 km,圆轨道且经过极区,其主要目的是研究与地震有关的电离层异常.2008年5月12日6∶28（世界时）在四川省汶川县（31.02°N, 103.37°E）发生了M_s8.0级的特大地震.本文分析了在震前一周内DEMETER卫星观测到的电离层异常.这些异常主要包括：（1）卫星在震前4天和5天经过震中附近时,记录到电子浓度、电子温度和氧离子浓度出现剧烈变化（变化率均超过20%）;（2）在震前3天和7天,卫星探测到增强的电磁辐射.同时利用ELF频段（0~1250 Hz）的三分量电场和磁场数据,对异常电磁辐射作了进一步的分析（计算了电场功率谱、磁场功率谱、波矢方向和极化特性等）.另外,考查了观测期间的地磁指数,由此得出观测到的异常现象不大可能由地磁活动引起.最后,对震前出现的这些电离层异常的可能的物理机理进行了讨论.     

北方玉米冠层光合有效辐射垂直分布及影响因子分析

玉米冠层内光合有效辐射(PAR)的大小直接影响冠层内叶片的光合作用,进而影响玉米净第一性生产力或作物产量的准确评估。为弄清玉米冠层内光合有效辐射的分布规律及其影响因子,基于锦州玉米农田生态系统于2006年生育期的光合有效辐射观测数据和叶面积指数动态观测数据,对玉米冠层光合有效辐射的垂直分布特征及其影响因子进行了分析。结果表明:玉米冠层内不同垂直层次叶片的PAR分布随生育期变化显著,与叶面积指数呈显著的负相关(R2=0.89);玉米冠层光合有效辐射的消光系数K值在生育期呈动态变化,约为0.76,且表现为苗期较大、生育后期较小。分析表明,在进行光合有效辐射及与此密切相关的光合作用模拟时,应考虑消光系数的动态变化。     

盘锦芦苇湿地空气动力学参数动态特征及其影响因素分析

应用盘锦芦苇生态系统观测场的涡度相关通量观测系统和小气候梯度系统的观测资料,估算了芦苇下垫面的空气动力学参数,并分析了其影响因素。结果表明:芦苇湿地零平面位移d和粗糙度Z0的季节变化总体呈现先增加后减少的单峰曲线变化规律。Z0和d均在9月达到最大,分别为0.24 m和1.85 m;12月达到最小,分别为0.03 m和0.02 m。芦苇湿地的Z0和d的季节变化主要受叶面积指数(LAI)、株高(h)及风速的影响。d随h的增加而单调增加,Z0随着h的变化遵循二次曲线,d/h、Z0/h与LAI之间的复相关系数分别为0.99和0.78。研究亦表明,大气稳定度和风向也对d和Z0有一定的影响。     

影响植被内部辐射状况的冠层结构特征研究

植被冠层结构特征是影响植被内部辐射状况的重要因子之一,对于植被群体的光合特性来说,冠层结构特性影响了光合有效辐射的截获、吸收和透射。本文着重分析了冠层结构的数量特征（如叶面积指数）和冠层几何结构特征,综合考虑叶倾角、叶方位角和Ｇ函数等群体几何特征,以便直接用于遥感光合植被生物量机理估测模型的建立。     

Estimating fractional vegetation cover from leaf area index and clumping index based on the gap probability theory

Gap probability theory provides a theoretical equation to calculate fractional vegetation cover (FVC). However, the main algorithms used in present FVC products generation are still the linear mixture model and machine learning methods. The reason to limit the gap probability theory applied in the product algorithm is the availability and accuracy of leaf area index (LAI) and clumping index (CI) products. With the improvement of the LAI and CI products, it is necessary to assess whether the algorithm based on gap probability theory using the present products can improve the accuracy of FVC products. In this study, we generated the FVC estimates based on the gap probability theory (FVCgap) with a resolution of 500 m every 8 days for Europe. FVCgap estimates were validated with field FVC measurements of ImagineS from 2013 to 2015 for crop types. Two existing FVC products, Geoland2 Version1 (GEOV1) and Multisource data Synergized Quantitative remote sensing production system (MuSyQ), were used to inter-compare with the FVCgap estimates. FVCgap estimates showed a better agreement with field FVC measurements, with lowest root mean square error (RMSE) (0.1211) and bias (0.0224), than GEOV1 and MuSyQ FVC products. The inter-annual and seasonal variations of FVCgap estimates were also showed the most consistent with field measurements.     

人工蜂群算法优化SVR的叶面积指数反演

支持向量机回归SVR（Support Vector Regression）方法作为叶面积指数反演的一种新思路,在LAI反演中具有一定的应用价值和前景,但SVR算法中惩罚系数C、核函数宽度参数g、不敏感损失函数参数ε的取值对回归精度有显著的影响。本文提出了一种基于人工蜂群算法ABC（Artificial Bee Colony）优化SVR参数的遥感影像叶面积指数反演方法。研究数据为美国土壤水分实验（SMEX02）2002年LAI实测数据和同期的Landsat 7 ETM+地表反射率数据,为了验证ABC算法优化SVR各个参数对反演精度的影响,建立了未优化参数（SVR）、优化单个参数（ABC-SVR-C,ABC-SVR-g,ABC-SVR-ε）、优化3个参数（ABC-SVR）的3类LAI反演模型,并比较了其回归拟合精度。在此基础上,分析了3个关键参数对LAI反演模型精度的敏感性,并对ABC算法优化SVR模型的精度进行显著性检验。研究表明：（1）相比未优化参数模型,ABC算法优化模型具有更高的反演精度,优化3个参数优于优化单个参数,回归直线斜率k达到0.797、决定系数r²达到0.775。（2）SVR的3个关键参数对模型精度都有影响,相较参数C和g,参数ε引起模型精度的不确定性更高。（3）95%的置信区间下,ABC-SVR模型与SVR模型的回归直线斜率k、r²、RMSE的差异显著性检验P值均小于0.005,ABC算法显著改善了SVR模型的精度。     

Simulation analysis on the relationship between the leaf area index and polarimetric parameters of crops

Abstract

The leaf area index (LAI) is an important parameter to quantitatively describe the structure of vegetation and crops. Uncertainty in the relationship between the LAI and polarimetric parameters is the key problem for LAI estimation from polarimetric synthetic aperture radar (POLSAR) data. However, the existing POLSAR data have difficulties meeting the demand of the aforementioned research. This paper analyses the correlations between the LAI and the polarimetric parameters derived from Cloude and Freeman decompositions using simulated POLSAR data based on a coherent scattering model for maize and wheat. The results show: (1) The POLSAR data at C-band with a large incidence angle (40 degrees) are very suitable for finding the LAI for maize and wheat. (2) For maize there is a strong correlation between the scattering type angle and the LAI at C-band with a large incidence angle, and the coherency entropy, anisotropy, and the power of the double-bounce scattering power component also have significant correlations with the LAI. (3) For wheat at C-band with a high incidence angle, although the correlation coefficient is low, there is still a correlation between the entropy, anisotropy and LAI. Besides, the volume scattering is suitable for extracting the LAI for wheat at X-band.     

机载激光雷达森林叶面积指数反演研究

叶面积指数(LAI)是分析冠层结构最常用的参数之一,它控制着植被的生物物理过程,如光合、呼吸、蒸腾、碳循环和降水截获等,因此快速、可靠和客观地评价LAI非常重要.本文发展了激光穿透指数(LPI)的简化计算方法,首次利用校正后的回波强度计算出LPI,以LPI为变量基于Beer-Lambert定律实现了甘肃大野口研究区森林LAI反演,并且与原始回波强度和回波数反演LAI的精度进行对比,结果发现通过距离和角度校正后的回波强度值能提高LAI反演精度.为了评价模型的可靠性和泛化性能,用留一法交叉验证程序(LOOCV)对最佳反演模型进行了验证,表明该模型没有过度拟合,具有很好的泛化能力.最后,用没有参加建模的16个实测LAI对预测值进行精度验证(R²=0.810,RMSE=0.198),发现校正后的回波强度反演山区森林LAI精度较高.本文还对激光雷达LAI反演结果与传统光学TM影像的反演结果进行了对比分析,结果表明机载激光雷达反演LAI精度(R²=0.825,RMSE=0.165)高于光学TM遥感数据(R²=0.605,RMSE=0.257),因此,可用激光雷达数据实现研究区的高精度LAI反演,为生态环境研究提供可靠的基础数据.     

Mapping grassland leaf area index with airborne hyperspectral imagery: A comparison study of statistical approaches and inversion of radiative transfer models

Statistical and physical models have seldom been compared in studying grasslands. In this paper, both modeling approaches are investigated for mapping leaf area index (LAI) in a Mediterranean grassland (Majella National Park, Italy) using HyMap airborne hyperspectral images. We compared inversion of the PROSAIL radiative transfer model with narrow band vegetation indices (NDVI-like and SAVI2-like) and partial least squares regression (PLS). To assess the performance of the investigated models, the normalized RMSE (nRMSE) and R² between in situ measurements of leaf area index and estimated parameter values are reported. The results of the study demonstrate that LAI can be estimated through PROSAIL inversion with accuracies comparable to those of statistical approaches (R² = 0.89, nRMSE = 0.22). The accuracy of the radiative transfer model inversion was further increased by using only a spectral subset of the data (R² = 0.91, nRMSE = 0.18). For the feature selection wavebands not well simulated by PROSAIL were sequentially discarded until all bands fulfilled the imposed accuracy requirements.