Evaluation of simulated soil moisture from China Land Data Assimilation System (CLDAS) land surface models

ABSTRACT

This study evaluated the land surface model-simulated soil moisture (SM) product from the China Land Data Assimilation System (CLDAS). This was achieved using three densely instrumented in situ observation networks in China that have different environmental conditions, i.e., the Hebi, Naqu and Heihe sites. The European Space Agency Climate Change Initiative multi-satellite-retrieved SM product (CCI-SM) was also included for inter-comparison purposes. Standard validation scores indicated that the CLDAS-SM product has high correlation and low uncertainty with both surface and root-zone soil moisture observations. The target accuracy (0.04 m³ m^?3) was achieved over all three sites. Compared with the CCI-SM product, the CLDAS-SM product showed higher accuracy for the Hebi and Heihe sites but slightly lower accuracy for the Naqu site located at the centre of the Tibetan Plateau. Regionally, the unbiased root mean square difference between the CLDAS-SM and CCI-SM products was noticeably smaller within China than in neighbouring countries. Given that the performance of the CCI-SM product should be unaffected by country boundaries, the better performance of the CLDAS-SM product in China can be attributed primarily to the high-quality meteorological forcing data.     

An observation-driven optimization method for continuous estimation of soil moisture over large heterogeneous areas

ABSTRACT

In most remote sensing-based soil moisture (SM) retrieval methods, in-situ SM measurements are commonly used for validation purposes. Few studies have investigated whether such measurements can be used for calibration. In this paper, an observation-driven optimization method was proposed to estimate SM from remote sensing observations. Specifically, the optimization method was developed within the surface temperature-vegetation index (TVX) framework for the definition of objective function and constraints. In-situ SM measurements were used to optimize the theoretical boundaries of the TVX feature space. We demonstrated the applicability of the new method with Moderate Resolution Imaging Spectroradiometer (MODIS) products over the Southern Great Plains (SGP) of the United States of America. Results indicate that the accuracy produced using only one site for calibration has reached a level comparable with those produced by traditional methods. Moreover, the method has not only bypassed the complex parameterization of aerodynamic and surface resistance but also achieved continuous monitoring of SM. That is just the capacity that the traditional TVX method does not possess. Therefore, although our optimization method requires the ancillary of in-situ observations, its simplicity proves that it is a useful tool for a quick and continuous monitoring of SM over large heterogeneous areas.     

Land surface evapotranspiration estimation combining soil texture information and global reanalysis datasets in Google Earth Engine

ABSTRACT

Global accurate evapotranspiration (ET) maps are crucial to monitor the water balance on the Earth’s surface. For this purpose, Walker et al. (2019) developed a methodology to estimate ET (ET_WV), considering that the soil properties and moisture (SM) are important limiting factors. In this work ET_WV was assessed in different land covers, land uses and soil properties using FLUXNET data and climate reanalysis datasets available in Google Earth Engine (GEE). GEE application programming interface (API), a powerful programming tool for non-experienced user, was used here to derived global ET_WV maps. ET_WV, computed with in situ FLUXNET data resulted in an overall ubRMSE of about 1.58 mm d^?1. The ET_WV estimates with GEE datasets yielded RMSE at least 56% smaller than those published by the available weather datasets. So, ET_WV methodology showed to be suitable for deriving global ET maps from different sources of data.     

Expanding the applicability of remotely sensed soil evaporation transfer coefficient to the estimation of soil moisture over bare soil and partially vegetated areas

Soil evaporation transfer coefficient (h_a) is an effective means of estimating surface soil moisture from moderate-resolution imaging spectroradiometer (MODIS) imagery. This coefficient is a function of three variables: air temperature, land surface temperature and dry soil temperature. The first two variables can easily be obtained from different sources, whereas dry soil temperature cannot be determined as easily as the other ones, particularly over partially vegetated areas. In this paper, to enhance the capability of h_a in estimating soil moisture, we propose to use the combination of land surface temperature (LST) and normalized difference vegetation index (NDVI) to estimate dry soil temperature over partially vegetated areas as well as bare soil areas; this combination is known as LST-NDVI feature space in the literature. The underlying assumption of the proposed method is that at any given pixel over partially vegetated or bare soil areas, dry soil temperature is approximately equivalent to the maximum LST derived from LST-NDVI triangle space. The results showed that calculating h_a using dry soil temperature derived from the triangle space can result in more reliable estimation of soil moisture over bare soil and partially vegetated areas.     

Uncertainty evaluation at three spatial scales for the NDVI-based VWC estimation method used in the SMAP algorithm

Vegetation water content (VWC) is the key input parameter for a soil moisture retrieval algorithm based on microwave remote sensing, and VWC uncertainty can limit the estimated accuracy of soil moisture. There has been little research on VWC algorithm development and validation in China, and the uncertainty of the VWC estimation method has not been well evaluated. Therefore, the aim of this study is to evaluate the uncertainty of the VWC estimation method used in the SMAP (Soil Moisture Active Passive) algorithm on three spatial scales (the point-scale, 30 m scale, and 1 km scale) for maize in northeast China. Results from three ground experimental datasets showed that the SMAP VWC estimation method was strongly biased with an average overestimation of 1.16 kg m^?2,1.04 kg m^?2, and 1.13 kg m^?2 for the point-scale, 30 m scale, and 1 km scale respectively, and maximum bias occurred in the mid-stage of maize. Also, a new power relationship between NDVI (Normalized Difference Vegetation Index) and VWC was proposed for the 30 m scale based on Sentinel 2 NDVI and field VWC values from 2017 experiment, with respective R² (coefficient of determination) and Root Mean Squared Error (RMSE) values of 0.80 and 0.67 kg m^?2. The results confirmed that this power relationship was still suitable for VWC estimation at the 1 km scale, and it has smaller bias than the original SMAP VWC method. Future work will be carried out to evaluate the applicability of this VWC estimation method over a lager region. It is expected that it can improve the accuracy of soil moisture by providing high precision VWC input parameters.     

Assessment of the relationship between thermal-infrared-based temperature−vegetation dryness index and microwave satellite-derived soil moisture

Soil moisture (SM) is an important parameter in terrestrial ecological and hydrological processes, particularly in arid and semi-arid regions. However, a highly accurate SM grid data set, which is used as a reference for the data quality, is not really suitable for the validation of other SM products. Thus, a more effective method may be necessary for evaluation of SM grid data. The temperature?vegetation dryness index (TVDI), which is estimated by the relationship between land surface temperature and vegetation index data, has been developed to assess regional water stress. Based on previous studies, we assumed a negative linear relationship between SM and the TVDI to establish the evaluation method of SM grid data. Although a highly accurate measure of SM obtained by use of microwave sensors may not always exhibit a negative linear correlation with the TVDI, the pixels of strong negative linear correlation between them signifies at least a higher accuracy of the two data at that position. The negative relationships between microwave satellite sensor-derived SM and the TVDI were tested by application of 16-day scaled satellite data in the Sahel. We determined that the correlations differ spatially according to vegetation distribution. That is, when compared with a lower correlation in the arid Sahara to the north, a higher correlation (?0.9 < r < ?0.7) was observed in the savannas, shrublands, and grasslands to the south. Our comparison results will be useful in developing validation methodologies for SM grid data in an alternative way under conditions of insufficient in situ measurements.     

Soil moisture monitoring using GNSS interference signal: proposing a signal reconstruction method

ABSTRACT

Soil moisture monitoring using Global Navigation Satellite System (GNSS) interference signal has gained wide interests in recent years. It utilizes the variation pattern of the routinely measured Signal-to-Noise Ratio (SNR) that contains the interference information between the direct and soil reflected signal. Previous studies have shown that the amplitude of the de-trended SNR data is not a good indicator for soil moisture variation. The possible cause found in this study is that the de-trending operation only reduces the additive direct signal component in the SNR data, while the multiplicative direct signal component in the amplitude of SNR data is unaffected. Therefore, a method is proposed to reduce the contamination of the direct signal component on the amplitude through signal reconstruction and then normalization. Experiment data are collected and processed to calculate the normalized amplitude based on the reconstruction method. The results show that the overall correlation coefficient of the normalized amplitude with in-situ soil moisture reaches to 0.6966 under highly rough surface condition, while it is only 0.4314 for the amplitude obtained from the conventional method. A quadratic model is used to retrieve soil moisture from the normalized amplitude, the retrieval error is less than 0.085 cm³ cm^?3.     

A model of prediction and cross-validation of fat-free mass in men with motor complete spinal cord injury

Gorgey AS, Dolbow DR, Gater DR Jr. A model of prediction and cross-validation of fat-free mass in men with motor complete spinal cord injury.ObjectivesTo establish and validate prediction equations by using body weight to predict legs, trunk, and whole-body fat-free mass (FFM) in men with chronic complete spinal cord injury (SCI).DesignCross-sectional design.SettingResearch setting in a large medical center.ParticipantsIndividuals with SCI (N=63) divided into prediction (n=42) and cross-validation (n=21) groups.InterventionNot applicable.Main Outcome MeasureWhole-body FFM and regional FFM were determined by using dual-energy x-ray absorptiometry. Body weight was measured by using a wheelchair weighing scale after subtracting the weight of the chair.ResultsBody weight predicted legs FFM (legs FFM=.09×body weight+6.1; R²=.25, standard error of the estimate [SEE]=3.1kg, P<.01), trunk FFM (trunk FFM=.21×body weight+8.6; R²=.56, SEE=3.6kg, P<.0001), and whole-body FFM (whole-body FFM=.288×body weight+26.3; R²=.53, SEE=5.3kg, P<.0001). The whole-body FFM_predicted (FFM predicted from the derived equations) shared 86% of the variance in whole-body FFM_measured (FFM measured using dual-energy x-ray absorptiometry scan) (R²=.86, SEE=1.8kg, P<.0001), 69% of trunk FFM_measured, and 66% of legs FFM_measured. The trunk FFM_predicted shared 69% of the variance in trunk FFM_measured (R²=.69, SEE=2.7kg, P<.0001), and legs FFM_predicted shared 67% of the variance in legs FFM_measured (R²=.67, SEE=2.8kg, P<.0001). Values of FFM did not differ between the prediction and validation groups.ConclusionsBody weight can be used to predict whole-body FFM and regional FFM. The predicted whole-body FFM improved the prediction of trunk FFM and legs FFM.     

Measurement of glomerular filtration rate in adults: accuracy of five single-sample plasma clearance methods

Summary. After an intravenous injection of a tracer that is removed from the body solely by filtration in the kidneys, the glomerular filtration rate (GFR) can be determined from its plasma clearance. The method requires a great number of blood samples but collection of urine is not needed. In the present investigation the total plasma clearance of ⁵¹Cr-EDTA (ethylenediaminetetra-acetate) was assessed from 13 blood samples taken 5–300 min post-injection in 44 adult patients with GFR>15 ml min^-1. In 34 of these patients the plasma clearance of ⁹⁹Tc^m-DTPA (diethylenetri-aminepenta-acetate) was determined simultaneously. Using these clearance values as reference the accuracy of six simplified methods were studied: five single-sample methods and one five-sample method. The standard error of estimate (SEE) of the single-sample methods ranged from 4·2 to 7·5 ml min^-1 using EDTA, and from 3·8 to 6·3 ml min^-1 using DTPA. SEE of the five-samples method was 3·0 ml min^-1 (EDTA) and 3·1 ml min^-1 (DTPA). The single-sample methods given by Christensen & Groth (1986) and by Tauxe (1986) are recommended for daily use, as SEE was small even at low GFR values. In patients with GFR < 80 ml min^-1, in whom a highly accurate determination is needed, a multiple samples method is recommended, e.g., Brøchner-Mortensen (1972).     

增强MRI肿瘤-皮下脂肪信号强度比值鉴别椎管内神经鞘瘤与脊膜瘤北大核心CSCD

目的观察定量分析增强MRI所示椎管内神经鞘瘤(IS)和脊膜瘤(SM)肿瘤-皮下脂肪信号强度比值(SIR)鉴别二者的价值。方法回顾性分析76例经病理证实的IS(IS组,n=43)和SM(SM组,n=33)患者的术前MRI,由2名医师(医师1和医师2)分别测量增强T1WI所示肿瘤及皮下脂肪信号强度(SI),并计算其SIR;比较组间SIR异,采用受试者工作特征(ROC)曲线评价SIR鉴别IS与SM的效能,计算相应曲线下面积(AUC)。结果医师1测得IS组及SM组的SIR分别为0.91±0.12和0.62±0.09,医师2分别为0.88±0.12和0.64±0.10,IS组的SIR均高于SM组(Z=-6.825、-6.368,P均<0.01)。ROC曲线显示,医师1及医师2测量的SIR鉴别IS与SM的AUC分别为0.959和0.928;医师1测量SIR的最佳临界值为0.77时,其诊断敏感度为86.05%,特异度为100%;医师2测量SIR的最佳临界值为0.79时,其诊断敏感度为81.40%,特异度为96.97%。结论增强MRI所示IS肿瘤-皮下脂肪SIR高于SM,据此可有效鉴别二者。     

Enhancement of exchangeable Cd and Pb immobilization in contaminated soil using Mg/Al LDH-zeolite as an effective adsorbent

In the present study, experiments using zeolite and Mg/Al LDH-zeolite for immobilization of Cd and Pb ions in artificial soil were conducted. The conditions which affect Cd and Pb ion immobilization in soil were evaluated, namely soil pH (5–7), the mass ratio of adsorbents (1%, 3% and 5%), incubation time (15 days, 30 days and 45 days) and soil moisture (30%, 50% and 70%). The results indicated that the optimal soil pH, mass ratio of adsorbents, incubation time and soil moisture for immobilization of Cd and Pb ions by the adsorbent were, respectively, 7.0, 3%, 30 days and 70%. The exchangeable Cd ion content in the contaminated soil dropped from 22.17 mg kg⁻¹ (87.65%) to 11.03 mg kg⁻¹ (43.48%) and 6.47 mg kg⁻¹ (26.36%) on incubation with zeolite and Mg/Al LDH-zeolite, respectively, while the exchangeable Pb content fell from 23.28 mg kg⁻¹ (90.02%) to 14.12 mg kg⁻¹ (54.04%) and 9.47 mg kg⁻¹ (35.24%) using zeolite and Mg/Al LDH-zeolite as absorbents in contaminated soil, respectively. Fe–Mn oxide occluded (F2), carbonate bound (F3) and organically complexed (F4) were the main forms for immobilization of the exchangeable Cd and Pb when the zeolite and Mg/Al LDH-zeolite absorbents were separately cultivated into soil. Precipitation, co-precipitation and electrostatic attraction were the main mechanisms of exchangeable Cd and Pb immobilization onto the Mg/Al LDH-zeolite to form carbonate metals (CdCO₃ and PbCO₃). This was due to the surface functional groups of the adsorbent and the presence of Fe and Al oxyhydroxides, Mn oxides, and Si and O elements in the Mg/Al LDH-zeolite''s constituents. The efficiency of Cd and Pb immobilization by the Mg/Al LDH-zeolite was higher than that by zeolite from 1.5 to 1.6 times. The Mg/Al LDH-zeolite showed an enhanced ability of exchangeable Cd and Pb immobilization in contaminated soil.

In the present study, experiments using zeolite and Mg/Al LDH-zeolite for immobilization of Cd and Pb ions in artificial soil were conducted.     

99Tcm-TRODAT-1多巴胺转运蛋白SPECT脑显像在亚临床期和临床期帕金森病模型猴诊断中的研究

目的探讨99Tcm-TRODAT-1多巴胺转运蛋白SPECT脑显像在帕金森病亚临床期诊断中的价值.方法对4只食蟹猴静脉注射多巴胺转运蛋白显像剂99Tcm-TRODAT-1,观察99Tcm-TRODAT-1在不同时间点正常猴体内分布并进行纹状体DAT功能分析.用MPTP分别制备无症状亚临床期和临床期PD猴模型,利用计算机感兴趣区(ROI)技术进行纹状体DAT功能半定量分析.结果99Tcm-TRODAT-1最佳SPECT脑显像时间为注射99Tcm-TRODAT-1后3～4 h.PD猴毁损侧(右侧)纹状体在亚临床期就已存在DAT功能的降低,并随着损伤的加重毁损侧纹状体DAT功能进一步降低,对侧纹状体的DAT也受损.结论99Tcm-TRODAT-1 SPECT脑显像可用于PD的亚临床期诊断和病情监测.     

Validation of Global LAnd Surface Satellite (GLASS) fractional vegetation cover product from MODIS data in an agricultural region

Fractional vegetation cover (FVC) is an important parameter for describing the land surface vegetation conditions and widely used for land surface process simulations and global change studies. Global FVC products are mainly derived from satellite data and several global FVC products have been generated. Validation of the satellite FVC products is important before they can be applied. The objective of this study is to validate the newly generated Global LAnd Surface Satellite (GLASS) FVC product based on the time series of field FVC measurements in an agriculture region in the Heihe Basin of Northwest China. The high spatial resolution remotely sensed Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Compact Airborne Imaging Spectrometer (CASI) data were used to upscale the ground FVC measurements to validate the GLASS FVC product at 0.5 km spatial resolution. The results indicated that the GLASS FVC was highly accurate with the coefficient of determination (R²) of 0.86 and root-mean-square error (RMSE) of 0.087. Furthermore, the time series FVC profiles were consistent with the crop growing characteristics. It can be a reliable FVC product for agricultural applications.     

18F-FDG符合线路显像与99mTc-MDP骨显像及二者联合对乳腺癌骨转移的检出效能

目的 采用ROC曲线比较18F-FDG符合线路显像、99mTc-MDP骨显像及二者联合对乳腺癌骨转移的检出效能.方法 收集手术病理诊断为乳腺癌的女性患者113例,均于4周内先后接受18F-FDG符合线路显像及99mTc-MDP骨显像;对两种显像结果按5分法评分,以二者评分之和为联合评分值,以病理诊断或临床随访为确诊“金标准”,比较ROC曲线下面积(AUC),评价99mTc-MDP骨显像、18F-FDG符合线路显像及联合评分法对乳腺癌骨转移患者的检出效能,比较不同方法在各自最佳诊断阈值下的灵敏度、特异度、准确率、阳性预测值(PPV)和阴性预测值(NPV).结果 113例中,12例(10.62％)最终确诊为骨转移,101例(89.38％)无骨转移.99mTc-MDP骨显像、18 F-FDG符合线路显像以及二者联合诊断评分的ROC曲线分析显示三者AUC分别为0.991、0.874和0.993,三种方法对乳腺癌骨转移的诊断效能均佳,尤以99mTc-MDP骨显像与联合诊断为最佳(P均＜0.01).最佳阈值点下,单独18F-FDG符合线路显像、99mTc-MDP骨显像及联合检出骨转移患者的灵敏度分别为75.00％(9/12)、75.00％(9/12)、83.33％(10/12),特异度为100％(101/101)、98.02％(99/101)、98.02％(99/101),准确率为97.35％(110/113)、95.58％(108/113)、96.46％(109/113),PPV为100％(9/9)、81.82％(9/11)、83.33％(10/12),NPV为97.12％(101/104)、97.06％(99/102)、98.02％(99/101).结论 99mTc-MDP骨显像对乳腺癌骨转移患者的检出效能优于18F-FDG符合线路显像,二者联合可提高对骨转移患者的检出率.     

Suitability of hyperspectral data for monitoring nitrogen and phosphorus content in constructed wetlands

ABSTRACT

The nitrogen and phosphorus content in water and sediment is an important index for evaluating the nutritional status of wetland ecosystems. This study used an inversion model to assess the total nitrogen (TN) and total phosphorus (TP) content of constructed wetland using the canopy spectral reflectance data of four wetland plants. And then determine their relative suitability as a remotely sensed environmental monitoring tool. For water, the coefficient of determination (R²) of floating plants (up to 0.92) was higher than that of emergent plants (up to 0.82). For sediment, the R² of TN inversion for S. natans was 0.59 and that of TP inversion for L. minor was 0.52, suggesting that floating plant canopy spectral reflectance data are more useful for assessing water directly, while indicators for the sedimentary environment can be assessed using emergent plants. Overall, the results clearly show that it is feasible to estimate water and sediment TN and TP content using plant canopy spectral reflectance data, providing the basis for widespread, rapid, and reliable monitoring of wetland ecosystem health via hyperspectral remote sensing. This study provides a reference for the timely development of further wetland restoration and protection measures.     

Rapid error assessment for quantitative estimations from Landsat 7 gap-filled images

The failure of the Scan Line Corrector (SLC) of the Landsat ETM+ (Enhanced Thematic Mapper Plus) instrument in 2003 had resulted in missing values for 22% of each scene. As the remaining pixels were of high quality, several procedures had been developed to fill the gaps and increase the usability of the SLC-off images. In this letter, a methodology is presented to assess the error when estimating quantitative parameters from gap-filled Landsat 7 images. The error from the gap-filling procedure was estimated using an external reference image. The methodology was applied in a Mediterranean river basin using two types of gap-filling methods and the error was estimated for leaf area index (LAI), actual evapotranspiration (ET_a) and soil moisture in the rootzone (SM_rz), three remotely sensed products which are commonly used in hydrological studies. The results suggest that the interpolation method had lower errors in all examined products. The proposed methodology is an imperative step that each user of gap-filled products could use to estimate the associated error before using the maps.     

99mTc-EHIDA SPECT 30 min胆囊显像对内镜微创保胆手术治疗胆石症的指导价值

目的探讨~(99m)Tc-EHIDA SPECT 30 min胆囊显像对内镜微创保胆手术治疗胆石症的指导价值。方法回顾性分析因胆石症行胆囊~(99m)Tc-EHIDA SPECT显像的患者791例。其中,男388例,女403例,年龄(53.5±29.5)岁。对比分析~(99m)Tc-EHIDA SPECT 30 min胆囊显影结果与保胆治疗的情况。结果胆石症患者中,633例~(99m)Tc-EHIDA SPECT 30 min胆囊显影,提示胆囊管通畅,而158例患者~(99m)Tc-EHIDA SPECT 30 min胆囊未显影,提示胆囊功能异常。SPECT显示胆囊功能是否正常与保胆手术治疗胆石症之间的符合率为80.03%(633/791)。SPECT胆囊显影组与未显影组保胆率比较,差异有统计学意义(2=95.66,P=0.000),其优势比(OR)为7.91(95%CI:4.99～12.55)。结论~(99m)Tc-EHIDA SPECT 30 min胆囊显像是一种安全、快速、简便和非创伤性的检查方法,能够有效判断胆囊功能状态,对内镜微创保胆手术治疗胆石症有一定的指导作用。     

苯巴比妥钠介入99mTc-EHIDA肝胆显像诊断 先天性胆道闭锁的价值

目的 评价苯巴比妥钠介入99mTc-EHIDA肝胆显像诊断先天性胆道闭锁(BA)的临床价值.方法 应用SPECT仪器对58例临床上持续黄疸的婴儿服用苯巴比妥钠,5 mg·kg-1·d-1体重,分两次服用,连续一周后行99mTc-EHIDA肝胆显像,并经手术、病理诊断及随访确诊.结果 SPECT诊断为BA29例,经临床确诊为BA24例,婴儿肝炎综合征(HIS)5例;SPECT诊断为IHS29例,均经临床随访确诊.SPECT诊断BA的灵敏度为100%,特异性85.3%,准确度91.4%.结论 苯巴比妥钠联合99mTc-EHIDA肝胆显像是一种无创、安全、诊断效能高的检查方法,有助于明确病因,预测治疗效果,对于BA的诊断有较高的临床价值.