Forward simulation of gravity for crustal structure of Xiachayu-Gonghe profile in eastern Tibetan plateau

The crustal structure of Xiachayu-Gonghe geophysical profile in eastern Tibetan plateau is simulated with Bouguer anomaly corrected for sediments and lithosphere. The forward simulation shows that the thickness of upper crust in eastern Tibetan plateau is about 20 km, and the density is 2.78×103kg/m3. The bottom interface of middle crust changes from 30 km to 40 km, the density of middle crust is 2.89×103kg/m3. The materials with low density of 2.78 ×103kg/m3 exist in middle crust, and those with high density of 3.33 ×103kg/m3 exist at the bottom of middle crust between Wenquan and Tanggemu. The density is 3.10 ×103kg/m3 in lower crust. The shallowest depth of Moho interface is about 56 km, and the deepest one is about 74 km, the undulation of interface is large, the deep Moho is located in Xiachayu, Chayu, Nujiang, and Wenquan. The crustal density of eastern Tibetan plateau is larger than that of central section; the low velocity layers are located in middle crust and bottom in eastern Tibetan plateau and at the bottom of the upper crust in the central plateau.     

Ionospheric tomography based on GNSS observations of the CMONOC: performance in the topside ionosphere

This study carries out a quantitative analysis of the performance of ionospheric tomography in the topside ionosphere, utilizing data of October 2011 collected from 260 Global Navigation Satellite System (GNSS) stations in the Crustal Movement Observation Network of China. This tomographic reconstruction with a resolution of 2° in latitude, 2° in longitude and 20 km in altitude has more than 70 % of voxels traversed by GPS raypaths and is able to provide reliable bottom parts of ionospheric profiles. Compared with the observations measured by the Defense Meteorological Satellite Program (DMSP) satellites (F16, F17 and F18) at an altitude of 830–880 km, the results show that there is an overestimation in the reconstructed plasma density at the DMSP altitude, and the reconstruction is better during daytime than nighttime. In addition, the reconstruction at nighttime also indicates a solar activity and latitudinal dependence. In summary, with respect to DMSP measurements, the daytime bias is on average from ?0.32 × 10⁵/cm³ to ?0.28 × 10⁵/cm³, while the nighttime bias is between ?0.37 × 10⁵/cm³ and ?0.24 × 10⁵/cm³, and the standard deviation at daytime and at nighttime is, respectively, 0.082 × 10⁵/cm³ to 0.244 × 10⁵/cm³ and 0.086 × 10⁵/cm³ to 0.428 × 10⁵/cm³. This study suggests that vertical ionospheric profiles from other sources, such as ionosondes or GNSS occultation satellites, should be incorporated into ground-based GNSS topside tomographic studies.     

利用重力数据反演中国东海海域莫霍面深度

莫霍面是地壳与上地幔的分界面,莫霍面的研究有助于认识地球深部构造及演化。在以往的研究中,由于重力反演方法、使用资料不同,中国东海海域莫霍面深度反演结果有较大不确定性。通过收集中国东海海域高精度地形和自由空气重力异常数据,计算了布格重力异常并分析了其构造特征。提取了中国福建省大田至中国台湾省花莲剖面和中国东海陆架盆地至菲律宾海盆剖面的重力异常数据,采用人机交互正演、反演拟合技术得到了这两条剖面的地壳密度与莫霍面深度。通过向上延拓的方法提取了莫霍面所引起的重力异常,在两条剖面反演结果和地震探测结果的约束下进行Parker-Oldenburg界面反演,得到了该地区的莫霍面深度。反演结果显示,中国东海海域莫霍面深度的变化范围为-34.4~-8.8 km,其结构呈两凹两凸的特征。     

Seismo-ionospheric precursor of the 2008 Mw7.9 Wenchuan earthquake observed by FORMOSAT-3/COSMIC

The seismo-ionospheric precursor prior to the Mw7.9 earthquake near Wenchuan, China, on 12 May 2008 was observed by the FORMOSAT-3/COSMIC satellite constellation. By binning radio occultation observations, the three-dimensional ionospheric structure can be obtained to monitor the ionospheric electron density variation prior to the earthquake. It has been determined that near the epicenter the F2-peak height, hmF2, descends about 25 km and the F2-peak electron density, NmF2, decreases about 2 × 10⁵ el/cm³ around noon within 5 days prior to the earthquake. The integrated electron content decreases more than 2 TECU between 250 and 300 km altitude.     

Spatiotemporal mixed effects modeling for the estimation of PM2.5 from MODIS AOD over the Indian subcontinent

ABSTRACT

The physical processes associated with the constituents of the troposphere, such as aerosols have an immediate impact on human health. This study employs a novel method to calibrate Aerosol Optical Depth (AOD) obtained from the MODerate resolution Imaging Spectrometer (MODIS – Terra satellite) for estimating surface PM_2.5 concentration. The Combined Deep Blue Deep Target daily product from the MODIS AOD data acquired across the Indian Subcontinent was used as input, and the daily averaged PM_2.5pollution level data obtained from 33 monitoring stations spread across the country was used for calibration. Mixed Effect Models (MEM) is a linear model to deal with non-independent data from multiple levels or hierarchy using fixed and random effects of dependent parameters. MEM was applied to the dataset obtained for the period from January to August 2017. The MEM considers a fixed and random component, where the random components model the daily variations of the AOD – PM_2.5 relationships, site-specific adjustment parameters, temporal (meteorological) variables such as temperature, and spatial variables such as the percentage of agricultural area, forest cover, barren land and road density with the resolution of 10 km × 10 km. Estimation accuracy was improved from an R² value of 0.66 from our earlier study (when PM_2.5 was modeled against only AOD and site-specific parameters) toR² value of 0.75 upon the inclusion of spatiotemporal (meteorological) variables with increased % within Expected Error from 18% to 35%, reduced Mean Bias Error from 3.22 to 0.11 and reduced RMSE from 29.11 to 20.09. We also found that spline interpolation performed better than IDW and Kriging inefficiently estimating the PM_2.5 concentrations wherever there were missing AOD data. The estimated minimum PM_2.5 is 93 ± 25μg/m³ which itself is in the upper limit of the hazardous level while the maximum is estimated as 170 ± 70μg/m³. The study has thus made it possible to determine the daily spatial variations of PM_2.5 concentrations across the Indian subcontinent utilizing satellite-based AOD data.     

川藏公路中段地质灾害现象的航空遥感研究

川藏公路巴塘至林芝段位于我国青藏高原东南部,该地区是现今地壳运动十分强烈的地区之一,地形起伏强烈,气候变化多样,因此地质灾害十分发育,川藏公路就穿过这样一个复杂的地区。为查明公路沿线的地质灾害分布情况,90年代初,地矿部航空物探遥感中心沿川藏公路进行了彩色红外航空摄影,比例尺为1∶6万。通过彩色红外航片的解译及野外实地观测,圈定出滑坡、泥石流及崩塌等灾害现象,并对这些灾害的强度、活动性及其对公路的影响进行分析,最后对灾害成因及治理方法提出了建议。     

用变密度模型反演青藏高原的莫霍面深度

采用密度随深度呈指数变化的变密度模型来反演莫霍面深度，给出了利用指数密度模型在波数域中计算重力异常的正演公式压界面深度的反演公式。结果表明，青藏高原莫霍面呈现出边缘浅、中部深，边缘变化快、梯度大，中间变化梯度趋缓的特点。通过对常密度模型、变密度模型及地震反演得到的莫霍面的比较，证实变密度模型更适合于莫霍面结构的反演。     

Combined effect of pulse density and grid cell size on predicting and mapping aboveground carbon in fast-growing Eucalyptus forest plantation using airborne LiDAR data

Background

LiDAR remote sensing is a rapidly evolving technology for quantifying a variety of forest attributes, including aboveground carbon (AGC). Pulse density influences the acquisition cost of LiDAR, and grid cell size influences AGC prediction using plot-based methods; however, little work has evaluated the effects of LiDAR pulse density and cell size for predicting and mapping AGC in fast-growing Eucalyptus forest plantations. The aim of this study was to evaluate the effect of LiDAR pulse density and grid cell size on AGC prediction accuracy at plot and stand-levels using airborne LiDAR and field data. We used the Random Forest (RF) machine learning algorithm to model AGC using LiDAR-derived metrics from LiDAR collections of 5 and 10 pulses m^?2 (RF5 and RF10) and grid cell sizes of 5, 10, 15 and 20 m.

Results

The results show that LiDAR pulse density of 5 pulses m^?2 provides metrics with similar prediction accuracy for AGC as when using a dataset with 10 pulses m^?2 in these fast-growing plantations. Relative root mean square errors (RMSEs) for the RF5 and RF10 were 6.14 and 6.01%, respectively. Equivalence tests showed that the predicted AGC from the training and validation models were equivalent to the observed AGC measurements. The grid cell sizes for mapping ranging from 5 to 20 also did not significantly affect the prediction accuracy of AGC at stand level in this system.

Conclusion

LiDAR measurements can be used to predict and map AGC across variable-age Eucalyptus plantations with adequate levels of precision and accuracy using 5 pulses m^?2 and a grid cell size of 5 m. The promising results for AGC modeling in this study will allow for greater confidence in comparing AGC estimates with varying LiDAR sampling densities for Eucalyptus plantations and assist in decision making towards more cost effective and efficient forest inventory.

     

多视线向InSAR形变场约束的改则地震滑动分布反演

利用3种不同视线向LOS(Line Of Sight)的ENVISAT ASAR数据进行干涉处理,提取多视线向(Multi-LOS)的同震形变场;结合同震形变场特征与震源机制解,构建了改则地震双断层破裂模型;利用四叉树采样后的多视线向同震形变场进行约束,通过梯度下降法(Steepest Descent Method,SDM)与Crust2.0地壳分层模型反演了改则地震的同震滑动分布特征。结果表明:反演的形变残差得到有效控制,基本介于0±10 cm之间;主震断层的滑动量主要位于断层面2—16 km深部,最大滑动量可达1.34 m,位于断层面6.4 km深处;余震断层滑动量主要位于断层面2—6 km深部,最大滑动量可达0.90 m,位于断层面3.52 km深处;主震断层与余震断层均以正断为主,但主震断层还具有一定的左旋走滑分量,而余震断层的左旋走滑不明显;当剪切模量μ取3.2×1010Pa时,反演获得的主震与余震地震矩M0分别为6.34×1018N·M与1.20×1018N·M,分别相当于矩震级MW6.47与MW5.98。     

The geopotential to (14, 14) from a combination of satellite and gravimetric data

A set of2261 5°×5° mean anomalies were used alone and with satellite determined harmonic coefficients of the Smithsonian' Institution to determine the geopotential expansion to various degrees. The basic adjustment was carried out by comparing a terrestrial anomaly to an anomaly determined from an assumed set of coefficients. The (14, 14) solution was found to agree within ±3 m of a detailed geoid in the United States computed using1°×1° anomalies for an inner area and satellite determined anomalies in an outer area. Additional comparisons were made to the input anomaly field to consider the accuracy of various harmonic coefficient solutions. A by-product of this investigation was a new γ_E=978.0463 gals in the Potsdam system or978.0326 gals in an absolute system if −13.7 mgals is taken as the Potsdam correction. Combining this value of γ_E withf=1/298.25, KM=3.9860122·10 ²² cm ³ /sec ² , the consistent equatorial radius was found to be6378143 m.     

利用掩星技术研究南极地区顶部电离层特性

掩星观测能够提供地面到低轨卫星轨道高度处的整个电离层电子密度剖面,对于顶部电离层的研究有重要的作用。本文利用COSMIC(constellation observing system for meteorology ionosphere and climate)掩星数据反演了电子密度剖面,提取了F₂层峰值高度(hmF2)、F₂层峰值密度(NmF2)、垂直标尺高(vertical scale height,VSH)等电离层参数,研究了南极地区的F₂层在太阳活动周期内的变化、年际变化、周日变化等,并且重点分析了南极地区的顶部电离层的垂直结构特征,尤其是威德尔海异常在垂直方向上的变化。结果表明,整个南极的hmF2每日均值在250~300 km左右,NmF2每日均值在1~8×1011 el/m3之间,VSH每日均值在100~250 km,威德尔海异常主要表现在顶部电子密度的增强和底部电子密度的减少。     

Timber production assessment of a plantation forest: An integrated framework with field-based inventory,multi-source remote sensing data and forest management history

Timber production is the purpose for managing plantation forests, and its spatial and quantitative information is critical for advising management strategies. Previous studies have focused on growing stock volume (GSV), which represents the current potential of timber production, yet few studies have investigated historical process-harvested timber. This resulted in a gap in a synthetical ecosystem service assessment of timber production. In this paper, we established a Management Process–based Timber production (MPT) framework to integrate the current GSV and the harvested timber derived from historical logging regimes, trying to synthetically assess timber production for a historical period. In the MPT framework, age-class and current GSV determine the times of historical thinning and the corresponding harvested timber, by using a “space-for-time” substitution. The total timber production can be estimated by the historical harvested timber in each thinning and the current GSV. To test this MPT framework, an empirical study on a larch plantation (LP) with area of 43,946 ha was conducted in North China for a period from 1962 to 2010. Field-based inventory data was integrated with ALOS PALSAR (Advanced Land-Observing Satellite Phased Array L-band Synthetic Aperture Radar) and Landsat-8 OLI (Operational Land Imager) data for estimating the age-class and current GSV of LP. The random forest model with PALSAR backscatter intensity channels and OLI bands as input predictive variables yielded an accuracy of 67.9% with a Kappa coefficient of 0.59 for age-class classification. The regression model using PALSAR data produced a root mean square error (RMSE) of 36.5 m³ ha⁻¹. The total timber production of LP was estimated to be 7.27 × 10⁶ m³, with 4.87 × 10⁶ m³ in current GSV and 2.40 × 10⁶ m³ in harvested timber through historical thinning. The historical process-harvested timber accounts to 33.0% of the total timber production, which component has been neglected in the assessments for current status of plantation forests. Synthetically considering the RMSE for predictive GSV and misclassification of age-class, the error in timber production were supposed to range from −55.2 to 56.3 m³ ha⁻¹. The MPT framework can be used to assess timber production of other tree species at a larger spatial scale, providing crucial information for a better understanding of forest ecosystem service.     

闪电河流域农牧交错带微波遥感土壤水分产品评价

空间网格分辨率为9 km的SMAP (Soil Moisture Active and Passive)、0.1D (Degree)的ASCAT (The Advanced Scatterometer)、 25 km的FY-3B以及25 km ESA-CCI (European Space Agency-Climate Change Initiative)是较为广泛应用的卫星遥感土壤水分产品,对数据质量的评价是进一步应用于旱情监测、蒸散发估算等研究的前提。本研究基于2018年9月在闪电河流域内蒙古农牧交错带区域开展的碳、水循环与能量平衡遥感综合试验,采用近似同步的两种尺度观测数据即点尺度地面实测土壤水分数据以及面尺度(1 km×1 km)机载土壤水分数据,利用RMSE (Root Mean Square Error), MAE (Mean Absolute Error),R (Correlation Coefficient),Bias以及ubRMSE (unbiased Root Mean Square Error)等评价指标分别对SMAP, ASCAT, FY-3B, ESA-CCI土壤水分卫星遥感产品进行了评价。本研究利用机载土壤水分数据作为桥梁,实现了从点尺度地面实测土壤水分数据、至面尺度(1 km×1 km)机载土壤水分数据、再至粗格网面尺度(9 km×9 km、0.1 D×0.1 D、25 km×25 km)卫星遥感土壤水分产品的对比分析过程。利用地面观测值对机载观测土壤水分开展评价分析,发现在裸土区域,机载土壤水分数据与地面实测数据较为一致,RMSE, MAE, Bias, ubRMSE以及R值分别为0.033 cm~3/cm~3,0.030 cm~3/cm~3,-0.004 cm~3/cm~3, 0.033 cm~3/cm~3, 0.474。对卫星土壤水分产品的评价结果显示,SMAP的9 km土壤水分卫星产品与地面观测更为一致,其RMSE,MAE,Bias,ub RMSE以及R值分别为0.037 cm~3/cm~3,0.032 cm~3/cm~3,-0.008 cm~3/cm~3, 0.036 cm~3/cm~3, 0.507。SMAP, ASCAT, FY-3B以及ESA-CCI与机载土壤水分数据有更高的相关性,R值分别为0.735, 0.558, 0.558, 0.575。综上,闪电河流域实验区内的4种卫星遥感土壤水分产品中,SMAP产品与地面土壤水分、机载土壤水分数据均较为一致,其次是FY-3B与ESA-CCI。     

Spatially variable surface elevation changes and estimated melt water contribution of Continental Glacier in the Wind River Range,Wyoming, USA: 1966–2011

Seasonal snow melt in the Wind River Range, Wyoming, has been ending earlier over the last several decades leaving the region to rely more on supplemental melt water from mountain glaciers. This leads to the necessity of understanding recent glacial changes. This study uses elevation data from 1966, 2006 and 2011 to calculate surface elevation and volume changes that have occurred on Continental Glacier. Results indicate a mean volume change of ?0.034 ± 0.02 km³ and surface elevation change of ?0.36 ± 0.19 m y^?1 between 1966 and 2006. Detailed spatial analysis shows that the glacier is divided into two sections which are thinning at different rates (lower section: ?0.06±0.19 m y^?1; upper section: ?0.51 ± 0.19 m y^?1). The upper section has experienced 97% of the thinning (or 742.5 × 10³ m³ of melt water equivalent per year) and increased its rate since 2006 by 27.5%.     

Model anomalies for the earth from crustal data

Crustal data of surface elevations and depth of Moho (and densities) can be utilized to form model-earth anomalies. These model-anomalies can closely approximate the free-air anomaly field of the earth, and could thus be used to predict the latter. A review of several such models is presented, with some elaboration on model developments, procedures, data analysis and accuracies. One of the models approaches a prediction accuracy of ±10 mgal for5°×5° mean free-air anomalies, whose r.m.s. value was about30% higher.     

A technique for routinely updating the ITU-R database using radio occultation electron density profiles

Well credited and widely used ionospheric models, such as the International Reference Ionosphere or NeQuick, describe the variation of the electron density with height by means of a piecewise profile tied to the F2-peak parameters: the electron density, $N_m \mathrm{F2}$ N m F 2 , and the height, $h_m \mathrm{F2}$ h m F 2 . Accurate values of these parameters are crucial for retrieving reliable electron density estimations from those models. When direct measurements of these parameters are not available, the models compute the parameters using the so-called ITU-R database, which was established in the early 1960s. This paper presents a technique aimed at routinely updating the ITU-R database using radio occultation electron density profiles derived from GPS measurements gathered from low Earth orbit satellites. Before being used, these radio occultation profiles are validated by fitting to them an electron density model. A re-weighted Least Squares algorithm is used for down-weighting unreliable measurements (occasionally, entire profiles) and to retrieve $N_m \mathrm{F2}$ N m F 2 and $h_m \mathrm{F2}$ h m F 2 values—together with their error estimates—from the profiles. These values are used to monthly update the database, which consists of two sets of ITU-R-like coefficients that could easily be implemented in the IRI or NeQuick models. The technique was tested with radio occultation electron density profiles that are delivered to the community by the COSMIC/FORMOSAT-3 mission team. Tests were performed for solstices and equinoxes seasons in high and low-solar activity conditions. The global mean error of the resulting maps—estimated by the Least Squares technique—is between $0.5\times 10^{10}$ 0.5 × 10 10 and $3.6\times 10^{10}$ 3.6 × 10 10 elec/m $^{-3}$ ? 3 for the F2-peak electron density (which is equivalent to 7 % of the value of the estimated parameter) and from 2.0 to 5.6 km for the height ( $\sim $ ～ 2 %).     

The use of atmospheric dispersion in optical distance measurement

The development of lasers, new electro-optic light modulation methods, and improved electronic techniques have made possible significant improvements in the range and accuracy of optical distance measurements, thus providing not only improved geodetic tools but also useful techniques for the study of other geophysical, meteorological, and astronomical problems. One of the main limitations, at present, to the accuracy of geodetic measurements is the uncertainty in the average propagation velocity of the radiation due to inhomogeneity of the atmosphere. Accuracies of a few parts in ten million or even better now appear feasible, however, through the use of the dispersion method, in which simultaneous measurements of optical path length at two widely separated wavelengths are used to determine the average refractive index over the path and hence the true geodetic distance. The design of a new instrument based on this method, which utilizes wavelengths of6328 ? and3681 ? and3 GHz polarization modulation of the light, is summarized. Preliminary measurements over a5.3 km path with this instrument have demonstrated a sensitivity of3×10 ⁻⁹ in detecting changes in optical path length for either wavelength using1-second averaging, and a standard deviation of3×10 ⁻⁷ in corrected length. The principal remaining sources of error are summarized, as is progress in other laboratories using the dispersion method or other approaches to the problem of refractivity correction.     

Modeling biophysical properties of broad-leaved stands in the hyrcanian forests of Iran using fused airborne laser scanner data and ultraCam-D images

Inventories of mixed broad-leaved forests of Iran mainly rely on terrestrial measurements. Due to rapid changes and disturbances and great complexity of the silvicultural systems of these multilayer forests, frequent repetition of conventional ground-based plot surveys is often cost prohibitive. Airborne laser scanning (ALS) and multispectral data offer an alternative or supplement to conventional inventories in the Hyrcanian forests of Iran. In this study, the capability of a combination of ALS and UltraCam-D data to model stand volume, tree density, and basal area using random forest (RF) algorithm was evaluated. Systematic sampling was applied to collect field plot data on a 150 m × 200 m sampling grid within a 1100 ha study area located at 36°38′- 36°42′N and 54°24′–54°25′E. A total of 308 circular plots (0.1 ha) were measured for calculation of stand volume, tree density, and basal area per hectare. For each plot, a set of variables was extracted from both ALS and multispectral data. The RF algorithm was used for modeling of the biophysical properties using ALS and UltraCam-D data separately and combined. The results showed that combining the ALS data and UltraCam-D images provided a slight increase in prediction accuracy compared to separate modeling. The RMSE as percentage of the mean, the mean difference between observed and predicted values, and standard deviation of the differences using a combination of ALS data and UltraCam-D images in an independent validation at 0.1-ha plot level were 31.7%, 1.1%, and 84 m³ ha⁻¹ for stand volume; 27.2%, 0.86%, and 6.5 m² ha⁻¹ for basal area, and 35.8%, −4.6%, and 77.9 n ha⁻¹ for tree density, respectively. Based on the results, we conclude that fusion of ALS and UltraCam-D data may be useful for modeling of stand volume, basal area, and tree density and thus gain insights into structural characteristics in the complex Hyrcanian forests.     

中国西部地壳现今变形特征及其机制探讨

以中国大陆及周边10年来近400个GPS测站的复测资料为基础，获取并绘制了现今地壳水平运动与变形图像，结果表明：青藏块体内西半部南北向只存在微弱的缩短变化（5mm/a左右），东半部南北向则没有缩短的迹象，南北缩短的区域主要位于青藏块体南缘的喜马拉雅条带（约15mm/a），北缘中部的柴达木西区（约15mm/a）和青藏块体北面的天山块体及周围地区（约15mm/a）；青藏块体大约有10mm/a的东西拉张，但不均匀，自西向东经历了由弱到强再有所减弱的过程，整个西部地区东边缘的东向运动表现为南强北弱的左旋特征；川滇菱形块体不是逃逸块体而是变形块体；青藏块体东缘及附近地区是东向运动的消减区带，面应变结果显示，青藏块体周边以面收缩为主，内部则以面膨胀为主；其以北的地区以面收缩为主（但压中有张），面应变的量级为10^-8/a。这样的变形结果，若只靠来处于印度板块的北向挤压是无法解释的。由此并结合最新的地球物理研究成果可推断或证实，地壳下部来自南向的物质涌入是控制青藏块体乃至中国大陆形变的另一大动力源，甚至可能是主导动力源；或者具有深、浅立体活动的某种协同性。