Remote detection of bare soil moisture using a surface-temperature-based soil evaporation transfer coefficient

An approach for estimating soil moisture is presented and tested by using surface-temperature-based soil evaporation transfer coefficient (h_a), a coefficient recently proposed through the equation h_a = (T_s − T_a)/(T_sd − T_a), where T_s, T_sd, and T_a are land surface temperature (LST), reference soil (dry soil without evaporation) surface temperature, and air temperature respectively. Our analysis and controllable experiment indicated that h_a closely related to soil moisture, and therefore, a relationship between field soil moisture and h_a could be developed for soil moisture estimation. Field experiments were carried out to test the relationship between h_a and soil moisture. Time series Aqua-MODIS images were acquired between 11 Sep. 2006 and 1 Nov. 2007. Then, MODIS derived h_a and simultaneous measured soil moisture for different soil depths were used to establish the relations between the two variables. Results showed that there was a logarithmic relationship between soil moisture and h_a (P < 0.01). These logarithmic models were further validated by introducing another ground-truth data gathered from 46 meteorological stations in Hebei Province. Good agreement was observed between the measured and estimated soil moisture with RMSE of 0.0374 cm³/cm³ and 0.0503 cm³/cm³ for surface energy balance method at two soil depths (10 cm and 20 cm), with RMSE of 0.0467 cm³/cm³ and 0.0581 cm³/cm³ for maximum temperature method at two soil depths. For vegetated surfaces, the ratio of h_a and NDVI suggested to be considered. The proposed approach has a great potential for soil moisture and drought evaluation by remote sensing.     

太湖水体的总磷分布及湖流对其影响的数值研究

用数值模拟的方法研究了太湖水体中ＴＰ分布特征及湖流对其影响,推导,建立了包括平流,水平扩散,沉降和底泥释放的浅水湖泊中污染物浓度分布计算的二维迎风有限元数值模式,并在给定若干点源条件下计算各种稳态流场下太湖水体中的ＴＰ分布。     

主成分监督分类及其在水质特征遥感图像识别中的应用

建立了一种水域水质状况图像识别的主成分监督分类方法,首先通过ＴＭ水域图像数据的主成分分析,将原有各波段图谱的显著且独立的信息集中在数目尽可能少的合成图象中,再依据不同类型水体的光谱特征,分析各主成分图像的构成及其环境生态学含义,由此对整个研究区域内存在的不同标志类型及其分布特征有所了解,在此基础上,选定训练样本集,从而人有清楚的环境生态意义的标志类型,应用监督法得到较好的识别分类结果,分析表明,这     

秦祁结合部位宝鸡地区早泥盆世香泉A型正长花岗岩年龄、地球化学特征及其构造意义

对秦祁结合部位宝鸡地区香泉正长花岗岩进行了LA-ICP-MS锆石U-Pb年龄和岩石地球化学研究。结果显示,锆石~(206)Pb/~(238)Pb年龄加权平均值为410±5Ma(MSWD=0.20,n=18),限定该岩体的形成时代为早泥盆世。香泉正长花岗岩具有高硅(SiO_2=69.63%~73.94%)、富钾(K_2O=4.24%~4.88%,K_2O/Na_2O=1.23~1.44)、富铁(TFe_2O_3=2.10%~3.70%,TFe_2O_3/MgO=3.88~6.84)、低镁(MgO=0.31%~0.94%)、低磷(P_2O_5=0.08%~0.21%)的特征,属准铝质、高钾钙碱性系列。香泉正长花岗岩稀土元素含量较高(318×10~(-6)~499×10~(-6)),表现出明显的负Eu异常(δ Eu=0.37~0.46),富集Rb、Th、Zr、Sm、Ga(10000×Ga/Al=2.59~2.93)等微量元素,贫Ba、Nb、Ta、Sr,整体表现出A型花岗岩特征。结合区域资料认为,香泉正长花岗岩形成于造山后环境,为低压环境下长英质地壳物质部分熔融成因。     

结合数学形态学与多角度模板匹配的高分辨率遥感图像救灾帐篷识别

从灾后遥感图像中快速准确地识别救灾帐篷有利于灾后救援工作的高效开展.本文结合实际应用需求,在前人研究的基础上,提出了一种结合数学形态学与多角度模板匹配的高分辨率遥感图像救灾帐篷识别方法.首先从遥感图像中选择帐篷模板并从中提取形状特征与光谱特征;然后将各波段灰度图像二值化并进行数学形态学运算,参考帐篷的形状特征提取出候选目标;最后根据帐篷的光谱特征,将候选目标与帐篷模板进行多角度匹配,剔除匹配度较低的伪目标,完成救灾帐篷识别.试验结果表明,本方法的识别精度达90%以上,具有较高的应用价值.     

A novel dynamic stretching solution to eliminate saturation effect in NDVI and its application in drought monitoring

The normalized difference vegetation index(NDVI) is one of the key input variables for developing drought indices.However,the NDVI quickly saturates in high vegetation surfaces,and thus,the generalization of a drought index over different ecosystems becomes a challenge.This paper presents a novel,dynamic stretching algorithm to overcome the saturation effect in NDVI.A scaling transformation function to eliminate saturation effects when the vegetation fraction(VF) is large is proposed.Dynamic range adjustment is conducted using three coefficients,namely,the normalization factor(a),the stretching range controlling factor(m),and the stretching size controlling factor(e).The results show that the stretched NDVI(S-NDVI) is more sensitive to vegetation fraction than NDVI when the VF is large,ranging from 0.75 to 1.00.Moreover,the saturation effect in NDVI is effectively removed by using the S-NDVI.Further analysis suggests that there is a good linear correlation between the S-NDVI and the leaf area index(LAI).At the same time,the proposed S-NDVI significantly reduces or even eliminates the saturation effect over high biomass.A comparative analysis is performed between drought indices derived from NDVI and S-NDVI,respectively.In the experiment,reflectance data from the moderate resolution imaging spectroradiometer(MODIS) products and in-situ observation data from the meteorological sites at a regional scale are used.In this study,the coefficient of determination(R2) of the stretched drought index(S-DI) is above 0.5,indicating the reliability of the proposed algorithm with surface soil moisture content.Thus,the S-DI is suggested to be used as a drought index in extended regions,thus regional heterogeneity should be taken into account when applying stretching method.     

城市化过程中半城市化地区社区人居环境特征研究——以厦门市集美区为例

城市化过程中半城市化地区存在着城市化程度由低到高的农村社区、城乡过渡型社区以及居住小区等城市型社区,社区人居环境多样化、多变化。在城市化影响下,这些社区人居环境呈现一定的特征。以厦门市集美区为例,通过选取典型社区,分析其景观格局特征,构建人居环境评价指标体系,对城市化过程中半城市化地区不同类型社区的人居环境特征进行了研究。结果表明:①从农村到城乡过渡型社区,建筑面积比例显著增加,道路面积比例变化不大,而林地和草地面积比例逐渐减少,景观格局逐渐变为景观类型较单一、以现代建筑为优势景观的状态,景观趋于破碎化,形状略趋复杂,城市居住小区各类景观面积比例则相对合理,但景观高度破碎化、形状较规则。②城市化过程中各类型社区人居环境质量均逐渐变好,城乡过渡型社区和农村尤为明显,城市居住小区质量明显高于过渡型社区与农村,且除城中村之外,从农村到城市居住小区社区城市化程度与人居环境质量呈正相关关系。③城市化总体上促进了社区人居环境质量的提高,但对社区人居环境各方面的作用具有不同的规律,对于环境质量、人文环境等方面具有一定的负面影响。     

Definitions of natural-language spatial relations: Combining topology and directions

Because SQL for querying data from spatial databases is ineffective, the query based on natural or visual language becomes an attractive research field gradually. However, how to define and represent natural languages related to spatial data are still gigantic problems. Because existing models of direction relations can't describe by use of some common concepts. First of all, detailed direction relations are proposed to describe the directions related to the interior of spatial objects, such as “east part of a region”, “east boundary of a region”, and so on. Secondly, by integrating the detailed directions with exterior direction relations and topological relations, several NLSRs are defined, such as “a road goes across the east part of a lake”, “a river goes along the east boundary of a province”, etc. Finally, based on the NLSRs abovementioned, a natural spatial query language (NSQL) is formed to retrieve data from spatial databases.     

A 3-dimensional data model for visualizing cloverleaf junction in a city model

The research work has been seldom done about cloverleaf junction expression in a 3-dimensional city model (3DCM). The main reason is that the cloverleaf junction is often in a complex and enormous construction. Its main body is bestraddle in air, and has aerial intersections between its parts. This complex feature made cloverleaf junction quite different from buildings and terrain, therefore, it is difficult to express this kind of spatial objects in the same way as for buildings and terrain. In this paper, authors analyze spatial characteristics of cloverleaf junction, propose an all-constraint points TIN algorithm to partition cloverleaf junction road surface, and develop a method to visualize cloverleaf junction road, surface using TIN. In order to manage cloverleaf junction data efficiently, the authors also analyzed the mechanism of 3DCM data management, extended BLOB type in relational database, and combined R-tree index to manage 3D spatial data. Based on this extension, an appropriate data structure for cloverleaf junction in 3DCM is proposed.     

Monitoring global land surface drought based on a hybrid evapotranspiration model

The latent heat of evapotranspiration (ET) plays an important role in the assessment of drought severity as one sensitive indicator of land drought status. A simple and accurate method of estimating global ET for the monitoring of global land surface droughts from remote sensing data is essential. The objective of this research is to develop a hybrid ET model by introducing empirical coefficients based on a simple linear two-source land ET model, and to then use this model to calculate the Evaporative Drought Index (EDI) based on the actual estimated ET and the potential ET in order to characterize global surface drought conditions. This is done using the Global Energy and Water Cycle Experiment (GEWEX) Surface Radiation Budget (SRB) products, AVHRR-NDVI products from the Global Inventory Modeling and Mapping Studies (GIMMS) group, and National Centers for Environmental Prediction Reanalysis-2 (NCEP-2) datasets. We randomly divided 22 flux towers into two groups and performed a series of cross-validations using ground measurements collected from the corresponding flux towers. The validation results from the second group of flux towers using the data from the first group for calibration show that the daily bias varies from −6.72 W/m² to 12.95 W/m² and the average monthly bias is −1.73 W/m². Similarly, the validation results of the first group of flux towers using data from second group for calibration show that the daily bias varies from −12.91 W/m² to 10.26 W/m² and the average monthly bias is −3.59 W/m². To evaluate the reliability of the hybrid ET model on a global scale, we compared the estimated ET from the GEWEX, AVHRR-GIMMS-NDVI, and NECP-2 datasets with the latent heat flux from the Global Soil Wetness Project-2 (GSWP-2) datasets. We found both of them to be in good agreement, which further supports the validity of our model's global ET estimation. Significantly, the patterns of monthly EDI anomalies have a good spatial and temporal correlation with the Palmer Drought Severity Index (PDSI) anomalies from January 1984 to December 2002, which indicates that the method can be used to accurately monitor long-term global land surface drought.