Quantifying snow water equivalent using terrestrial ground penetrating radar and unmanned aerial vehicle photogrammetry

This study demonstrates the potential value of a combined unmanned aerial vehicle (UAV) Photogrammetry and ground penetrating radar (GPR) approach to map snow water equivalent (SWE) over large scales. SWE estimation requires two different physical parameters (snow depth and density), which are currently difficult to measure with the spatial and temporal resolution desired for basin-wide studies. UAV photogrammetry can provide very high-resolution spatially continuous snow depths (SD) at the basin scale, but does not measure snow densities. GPR allows nondestructive quantitative snow investigation if the radar velocity is known. Using photogrammetric snow depths and GPR two-way travel times (TWT) of reflections at the snow-ground interface, radar velocities in snowpack can be determined. Snow density (RSN) is then estimated from the radar propagation velocity (which is related to electrical permittivity of snow) via empirical formulas. A Phantom-4 Pro UAV and a MALA GX450 HDR model GPR mounted on a ski mobile were used to determine snow parameters. A snow-free digital surface model (DSM) was obtained from the photogrammetric survey conducted in September 2017. Then, another survey in synchronization with a GPR survey was conducted in February 2019 whilst the snowpack was approximately at its maximum thickness. Spatially continuous snow depths were calculated by subtracting the snow-free DSM from the snow-covered DSM. Radar velocities in the snowpack along GPR survey lines were computed by using UAV-based snow depths and GPR reflections to obtain snow densities and SWEs. The root mean square error of the obtained SWEs (384 mm average) is 63 mm, indicating good agreement with independent SWE observations and the error lies within acceptable uncertainty limits.     

A PHYSICAL MODEL STUDY OF SCATTERING OF WAVES BY ALIGNED CRACKS: COMPARISON BETWEEN EXPERIMENT AND THEORY1

An approximation to plane-wave propagation through a composite material is examined using a physical model with oriented but randomly distributed penny-shaped rubber inclusions within an isotropic epoxy resin matrix. A pulse transmission method is used to determine velocities of shear and compressional waves as a function of angle of incidence and crack density. The experimental and theoretical results of Hudson were compared and limitations within the crack parameters used in this study have been determined. Results from both polarized shear waves (S1, S2) compare favourably with the theory for a composite with up to 7% crack density, but theory and experiment diverge at higher crack densities. On the other hand, compressional-wave velocities at low crack densities (1% and 3%) compare favourably with the theory. It is also shown that the velocity ratio V_p/V_s for two extreme cases, i.e. propagation normal and parallel to the cracks, as a function of crack density and porosity, has a strong directional dependence.     

A Monte Carlo study of rainfall forecasting with a stochastic model

A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities.     

APOD卫星大气密度数据处理与标校

APOD卫星是我国首颗以热层大气密度探测与精密定轨为科学目标的微纳卫星,搭载大气密度探测器、双频GNSS接收机等载荷,于2015年9月20日发射入轨,2015年10月27日进入轨道高度460 km、轨道倾角97.4°、降交点地方时6∶20的工作轨道,各项载荷随即展开例行观测.本文给出了APOD卫星大气密度探测器的基本原理和数据处理流程,采用基于双行根数（TLE）反演获取的密度数据,对2015年12月至2016年12月的就位探测数据进行了标校,并与经验密度模式进行了比较.结果表明,反演密度与APOD卫星就位探测数据的线性相关性达到0.943,采用线性拟合与二次函数拟合的残差水平基本相当.两种不同方法标校密度相对于NRLMSIS00模式日均值误差的均值和标准偏差为10.1%、18.2%和5.1%、17.1%,二次函数标校略优于线性标校;相对于JB2008模式日均值误差的均值和标准偏差为0.6%、14.9%和3.9%、16.9%,线性标校略优于二次函数标校.总体而言,APOD卫星大气密度就位探测数据与常用经验模式精度基本一致,可为开展大气密度变化规律及应用研究提供数据基础.     

Constraints in 3D gravity inversion

A three-dimensional (3D) inversion program is developed to interpret gravity data using a selection of constraints. This selection includes minimum distance, flatness, smoothness and compactness constraints, which can be combined using a Lagrangian formulation. A multigrid technique is also implemented to resolve separately large and short gravity wavelengths. The subsurface in the survey area is divided into rectangular prismatic blocks and the problem is solved by calculating the model parameters, i.e. the densities of each block. Weights are given to each block depending on depth, a priori information on density and the density range allowed for the region under investigation. The present computer code is tested on modelled data for a dipping dike and multiple bodies. Results combining different constraints and a weight depending on depth are shown for the dipping dike. The advantages and behaviour of each method are compared in the 3D reconstruction. Recovery of geometry (depth, size) and density distribution of the original model is dependent on the set of constraints used. From experimentation, the best combination of constraints for multiple bodies seems to be flatness and a minimum volume for the multiple bodies. The inversion method is tested on real gravity data from the Rouyn-Noranda (Quebec) mining camp. The 3D inversion model for the first 10 km is in agreement with the known major lithological contacts at the surface; it enables the determination of the geometry of plutons and intrusive rocks at depth.     

Estimation of the high-latitude topside electron heat flux using DMSP plasma density measurements

The high-latitude ionosphere interfaces with the hot, tenuous, magnetospheric plasma, and a heat flow into the ionosphere is expected, which has a large impact on the plasma densities and temperatures in the high-latitude ionosphere. The value of this magnetospheric heat flux is unknown. In an effort to estimate the value of the magnetospheric heat flux into the high-latitude ionosphere, and show its effect on the high-latitude ionospheric plasma densities, we ran an ensemble of model runs using the Ionosphere Forecast Model (IFM) with different values of the heat flux through the upper boundary. These model runs included heating from both auroral and solar sources. Then, for each heat flux value, the plasma densities obtained from the model runs, at 840 km, were compared to the corresponding values measured by the DMSP F13 satellite. The heat flux value that gave the best comparison between the measured and calculated plasma densities was considered to be the best estimate for the topside heat flux. The comparison was conducted for a 1-year data set of the DMSP F13 measured plasma densities (4300 consecutive orbits). Our systematic IFM/DMSP plasma density comparisons indicate that when a zero magnetospheric downward heat flux is assumed at the upper boundary of the IFM model, on the average, the IFM underestimates the measured plasma densities by a factor of 2. A good IFM/DMSP plasma density comparison was achieved for each month in 1998 when for each month a constant heat flux was assumed at the upper boundary of the model. For the 12-month period, the heat flux values that gave the best IFM/DMSP plasma density comparisons varied on the average from −0.5×10¹⁰ to −1.5×10¹⁰ eV cm⁻² s⁻¹.     

Annual and seasonal variations in the low-latitude topside ionosphere

Annual and seasonal variations in the low-latitude topside ionosphere are investigated using observations made by the Hinotori satellite and the Sheffield University Plasmasphere Ionosphere Model (SUPIM). The observed electron densities at 600 km altitude show a strong annual anomaly at all longitudes. The average electron densities of conjugate latitudes within the latitude range ±25° are higher at the December solstice than at the June solstice by about 100% during daytime and 30% during night-time. Model calculations show that the annual variations in the neutral gas densities play important roles. The model values obtained from calculations with inputs for the neutral densities obtained from MSIS86 reproduce the general behaviour of the observed annual anomaly. However, the differences in the modelled electron densities at the two solstices are only about 30% of that seen in the observed values. The model calculations suggest that while the differences between the solstice values of neutral wind, resulting from the coupling of the neutral gas and plasma, may also make a significant contribution to the daytime annual anomaly, the E × B drift velocity may slightly weaken the annual anomaly during daytime and strengthen the anomaly during the post-sunset period. It is suggested that energy sources, other than those arising from the 6% difference in the solar EUV fluxes at the two solstices due to the change in the Sun-Earth distance, may contribute to the annual anomaly. Observations show strong seasonal variations at the solstices, with the electron density at 600 km altitude being higher in the summer hemisphere than in the winter hemisphere, contrary to the behaviour in NmF2. Model calculations confirm that the seasonal behaviour results from effects caused by transequatorial component of the neutral wind in the direction summer hemisphere to winter hemisphere.     

地震动随机函数模型研究(Ⅱ)——参数统计与模型验证

依场地类别进行了强震记录分组,对模型参数的变化规律进行了统计分析.在模型随机参数向量满足独立性假设的前提下,得到了地震动随机函数模型的联合概率密度函数.引入数论选点方法对地震动随机函数模型的概率空间进行剖分,可以较少的样本点描述概率空间.以所选模型参数代表点代入地震动随机函数模型,即可以得到地震动时程样本集合.在集合层次上对比了模型预测地震动与真实记录的差异,两者在均值谱和标准差谱层次上均吻合较好,证实了模型预测结果的合理性.     

Comparison between some methods for estimating thermospheric parameters using ionospheric incoherent scatter measurements

Three methods for estimating the atomic oxygen density and exospheric temperature using the ionospheric incoherent scatter measurements have been compared. These methods are based on the usage of the relationship obtained from the energy conservation equation. They are applicable under the conditions of the atmosphere composed of oxygen atoms and ions. The first method is based on the regression analysis of finding minimal deviations of the calculated electron densities (N) from the values measured at altitudes of 300–450 km. The second method is based on solving the set of equations of the analytical expression relating N to ionospheric characteristics. These equations are given for several altitudes. The third method is related to the selection of such atomic oxygen densities at which the neutral gas temperature remains constant at an altitude above 350 km. All methods give similar results. The calculations based on the measurements performed at the Irkutsk radar on September 23, 1998, showed that the atomic oxygen densities at 400 km, estimated using the first and second methods, account for 0.48 of the value predicted by the MSIS-86 model, and such densities estimated using the third method account for 0.59 of the model value. In this case the estimated exospheric temperatures are larger than the values obtained using the thermospheric model by 11% for the first and second methods and by 14% for the third method.     

Experimental verification of effective anisotropic crack theories in variable crack aspect ratio medium

Physical modelling of cracked/fractured media using downscaled laboratory experiments has been used with great success as a useful alternative for understanding the effect of anisotropy in the hydrocarbon reservoir characterization and in the crustal and mantle seismology. The main goal of this work was to experimentally verify the predictions of effective elastic parameters in anisotropic cracked media by Hudson and Eshelby–Cheng's effective medium models. For this purpose, we carried out ultrasonic measurements on synthetic anisotropic samples with low crack densities and different aspect ratios. Twelve samples were prepared with two different crack densities, 5% and 8%. Three samples for each crack density presented cracks with only one crack aspect ratio, whereas other three samples for each crack density presented cracks with three different aspect ratios in their composition. It results in samples with aspect ratio values varying from 0.13 to 0.26. All the cracked samples were simulated by penny‐shaped rubber inclusions in a homogeneous isotropic matrix made with epoxy resin. Moreover, an isotropic sample for reference was constructed with epoxy resin only. Regarding velocity predictions performed by the theoretical models, Eshelby–Cheng shows a better fit when compared with the experimental results for samples with single and mix crack aspect ratio (for both crack densities). From velocity values, our comparisons were also performed in terms of the ε, γ, and δ parameters (Thomsen parameters). The results show that Eshelby–Cheng effective medium model fits better with the measurements of ε and γ parameters for crack samples with only one type of crack aspect ratio.     

Bayesian spectral density approach for modal updating using ambient data

The problem of identification of the modal parameters of a structural model using measured ambient response time histories is addressed. A Bayesian spectral density approach (BSDA) for modal updating is presented which uses the statistical properties of a spectral density estimator to obtain not only the optimal values of the updated modal parameters but also their associated uncertainties by calculating the posterior joint probability distribution of these parameters. Calculation of the uncertainties of the identified modal parameters is very important if one plans to proceed with the updating of a theoretical finite element model based on modal estimates. It is found that the updated PDF of the modal parameters can be well approximated by a Gaussian distribution centred at the optimal parameters at which the posterior PDF is maximized. Examples using simulated data are presented to illustrate the proposed method. Copyright © 2001 John Wiley & Sons, Ltd.     

Seismic characterization of reservoirs with multiple fracture sets using velocity and attenuation anisotropy data

Knowledge about the spatial distribution of the fracture density and the azimuthal fracture orientation can greatly help in optimizing production from fractured reservoirs. Frequency-dependent seismic velocity and attenuation anisotropy data contain information about the fractures present in the reservoir. In this study, we use the measurements of velocity and attenuation anisotropy data corresponding to different seismic frequencies and azimuths to infer information about the multiple fracture sets present in the reservoir. We consider a reservoir model with two sets of vertical fractures characterized by unknown azimuthal fracture orientations and fracture densities. Frequency-dependent seismic velocity and attenuation anisotropy data is computed using the effective viscoelastic stiffness tensor and solving the Christoffel equation. A Bayesian inversion method is then applied to measurements of velocity and attenuation anisotropy data corresponding to different seismic frequencies and azimuth to estimate the azimuthal fracture orientations and the fracture densities, as well as their uncertainties. Our numerical examples suggest that velocity anisotropy data alone cannot recover the unknown fracture parameters. However, an improved estimation of the unknown fracture parameters can be obtained by joint inversion of velocity and attenuation anisotropy data.     

基于GRACE星载加速度计数据的热层密度反演

本文主要研究了利用GRACE星载加速度计数据反演热层密度.首先联合采用GRACE卫星2007—2009年星载加速度计数据和星载GPS数据进行动力学定轨并同时估计加速度计校正参数,依此对加速度计数据进行了校正.根据Sentman稀薄空气动力学方程计算卫星空气动力系数,对校正后的加速度计数据进行处理,反演得到了该时期沿轨热层大气密度.为分析反演密度的精度,将本文反演得到的GRACE-A卫星沿轨密度与Doornbos的解算结果,以及经验密度模型NRLMSISE00,HASDM模型进行比较分析.统计结果表明,本文反演结果比Doornbos系统性偏大约5%~8%,二者间的标准差(STD,standard deviation)在10%以内,具有较好的符合性.其差异主要是由于采用了不同的加速度标校以及空气动力系数计算策略.本文反演得到的热层密度较HASDM模型表现为正的系统性偏差且幅度在4%以内,而Doornbos的结果较HASDM模型约系统性偏小4%~7%,二者与HASDM模型的标准差均为30%左右.另外,本文反演密度与NRLMSISE00模型之间存在约30%~40%的系统性bias,其STD也在30%左右.     

基于面平均雨量误差修正的实时洪水预报修正方法

空间集总式水文模型的洪水预报精度会受到面平均雨量估计误差的严重影响.点雨量监测值的误差类型、误差大小以及流域的雨量站点密度和站点的空间分布都会影响到面平均雨量的计算.为提高实时洪水预报精度,本文提出了一种基于降雨系统响应曲线洪水预报误差修正方法.通过此方法估计降雨输入项的误差,从而提高洪水预报精度.此方法将水文模型做为输入和输出之间的响应系统,用实测流量和计算流量之间的差值做为信息,通过降雨系统响应曲线,使用最小二乘估计原理,对面平均雨量进行修正,再用修正后的面平均雨量重新计算出流过程.将此修正方法结合新安江模型使用理想案例进行检验,并应用于王家坝流域的16场历史洪水以及此流域不同雨量站密度的情况下,结果证明均有明显修正效果,且在雨量站密度较低时修正效果更加明显.该方法是一种结构简单且不增加模型参数和复杂度的实时洪水修正的新方法.     

Finite strain theories and comparisons with seismological data

All the finite strain equations that we are aware of that are worth considering in connection with the interior of the Earth are given, with the assumptions on which they are based and corresponding relationships for incompressibility and its pressure derivatives in terms of density. In several cases, equations which have been presented as new or independent are shown to be particular examples of more general equations that are already familiar. Relationships for deriving finite strain equations from atomic potential functions or vice versa are given and, in particular it is pointed out that the Birch-Murnaghan formulation implies a sum of power law potentials with even powers. All the equations that survive simple plausibility tests are fitted to the lower mantle and outer core data for the PEM earth model. For this purpose the model data are extrapolated to zero temperature, using the Mie-Grüneisen equation to subtract the thermal pressure (at fixed density) and the pressure derivative of this equation to substract the thermal component of incompressibility. Fitting of finite strain equations to such zero temperature data is less ambiguous than fitting raw earth model data and leads immediately to estimates of the low temperature zero pressure parameters of earth materials. On this basis, using the best fitting equations and constraining core temperature to give an extrapolated incompressibilityK ₀=1.6×10¹¹Pa, compatible with a plausible iron alloy, the following numerical data are obtained: Core-mantle boundary temperature 3770 K Zero pressure, zero temperature densities: lower mantle 4190 kg m^–3 outer core (solidified) 7500 kg m^–3 Zero pressure, zero temperature incompressibility of the lower mantle 2.36×10¹¹PaHowever, an inconsistency is apparent betweenP() andK() data, indicating that, even in the PEM model, in which the lower mantle is represented by a single set of parameters, it is not perfectly homogeneous with respect to composition and phase.     

重力数据3D密度成像中EXTR方法的各参数变化对反演结果的影响(英文)

Tikhonov正则化(TR)方法在重磁数据处理中发挥了重要的作用,本文在研究如何利用Tikhonov正则化方法方法解决重力数据3D反演的同时,深入讨论了可进一步提高拟合误差的Extrapolation Tikhonov正则化方法(EXTR)的原理,并就其参数选择方法及各参数对拟合误差、迭代次数及反演结果的影响进行研究。常密度及变密度组合模型试算结果表明,与TR方法相比,EXTR方法不仅可以达到解释人员设定的先验拟合误差水平,在计算时间及迭代次数相应增加的前提下有更高的拟合精度;同时其反演结果也更加紧致,进一步改善了TR反演结果的发散性;并且其反演数据范围更贴近预设模型参数范围,模型特征与预设模型密度分布吻合较好。     

Effects of various transport processes on the streaming ion density during the first stage of plasmaspheric refilling

The dependence of the first stage H⁺ plasmaspheric refilling density on various parameters is examined using a kinetic transport model. The first stage of refilling is defined as the time for the source cone to reach a quasi-steady-state level. Three influencing factors are examined in detail. The first two factors are actually studying numerical influences of physical phenomena. That is, the method of including these processes in the calculation is varied to determine the importance of calculational rigor. The two processes of interest are self-collisional feedback and the ambipolar electric field. The third influencing factor to be examined is the effect of coexistent energetic populations of the refilling rate. It is found that the results greatly depend on the method of incorporating self-collisions into the model, as the scattering and loss processes of the low-energy proton population interacting with itself has a significant influence on the early stage density. This interaction is particularly strong in the low-altitude region where the densities are high enough to substantially alter the distribution function. It is also found that the ambipolar electric field is the dominant force term, increasing the densities in the plasmasphere by accelerating the particles through the low-altitude scattering zone. The hot populations are found to have only a minor influence near the equatorial region, where they slow the H⁺ streams down and cause the density to slightly increase. The effects of hot ions are more pronounced in the streaming velocity and the temperature anistropy, but still confined to the equatorial region.     

亚暴期间电离层场向电流的分布特征——CHAMP卫星观测

场向电流在不同的等离子体区之间传递能量、动量和质量,是磁层与电离层之间的关键耦合过程.本文利用CHAMP卫星高精度的空间磁场测量数据,研究亚暴期间极区电离层场向电流的统计学分布特征.研究表明场向电流的大小与所在位置呈现明显的日夜和晨昏不对称性,具体为：（1）场向电流的大小与亚暴极光电急流指数（AL）密切相连,AL愈大,电流愈强,亚暴期间电流强度相对平静期来说可增加约5倍,昏侧和夜侧电流强度与AL指数的相关性较好,晨侧和白天侧两者相关性较差;（2）电流的峰值密度所在位置与AL指数的相关性不高,昏侧电流所处纬度低于晨侧,而夜晚电流所处纬度低于白天侧.     

Telescoping ore targets by geochemical exploration at multiple scales in Eastern Yunnan Pt geochemical province,southwestern China

Platinum has been one of the highly needed mineral resources in China. The geochemical exploration at two survey scales was applied in telescoping ore targets for the first time in Eastern Yunnan Pt geochemical province that was delineated using Pt data from flood plain sediments with extra-low sampling density. Our study was based on the delineations and assessments of both regional and local Pt anomalies using the Pt data by analyzing with C-OES the composite samples with two sampling densities. The composite samples were obtained by recomposing at two sampling densities the original stream sediment samples collected by the National Geochemical Mapping Project. Semi-variograms were used to quantitatively describe the variability of Pt anomalies and further analyze the factors controlling the variability. Pt resource potentials of both the regional Pt anomalies and the local Pt anomalies in the study area were estimated based on the geochemical block methods, respectively. It comes to the conclusions as follows. (1) From the regional to local Pt anomaly, the factors controlling their variability from the deep seated faults-basalts turn into the basalts-branch faults, which suggest that Semi-variograms could identify the geological factors controlling the variability of the Pt anomalies identified by the Pt data from the stream sediments with different sampling densities. (2) There exist two types of Pt anomalies in the study area. One is those displaying at sampling densities, and its average Pt concentration significantly increases with sampling density increasing. The other is getting weaker and/or disappears with sampling density increasing. This shows that TOTGEMS could gradually eliminate non-ore anomalies and keep ore anomalies. (3) The average Pt concentration of the local Pt anomaly blocks delineated using Pt data from stream sediments with sampling density of one composite per 16 km² is twice as much as that of the regional Pt anomaly blocks delineated using Pt data from stream sediments with sampling density of one composite per 64 km2. The Pt resource amount of the local Pt anomaly blocks is 60% of the regional anomaly blocks, but the area of the former is just 35% of the latter, which suggests that the Pt resource amount is mainly concentrated in its local anomalies, and that TOTGEMS has a good exploration function that efficiently approaches ore targets. Supported by National High-Tech Research & Development Program of China (863 Program) (Grant No. 2006AA06Z113) and National Natural Science Foundation of China (Grant No. 40772197)