反演地表质量变化的附有空间约束的三维加速度点质量模型法

重力卫星可以在相同误差尺度下对全球质量变化进行连续重复观测,并在近十余年来取得了巨大成功,探索重力卫星数据精化处理方法和相关应用研究具有重要意义.本文基于三维加速度点质量模型法的基本原理,进一步发展建立了时变重力场模型球谐位系数的变化和地面点质量变化的关系,可有效考虑地表质量变化导致的负荷形变的影响;引入等权形式、线性形式、指数形式和高斯形式的空间约束方法处理南北条带噪声和向下延拓导致的病态问题,并与零阶Tikhonov正则化方法进行对比分析.采用模拟数据和一个月的实测GRACE时变重力场模型计算全球质量变化,对三维加速度点质量模型法和几种空间约束方法进行对比分析验证.计算结果表明,对于3°等面积的全球格网质量点,高斯和指数形式空间约束方法的最优相关距离约为500 km,等权和线性形式空间约束方法的最优相关距离约为600 km,各方法均可有效处理条带噪声的影响,四种空间约束方法的计算效果优于零阶Tikhonov正则化方法,本文的相关方法为进一步利用三维加速度点质量模型法监测全球质量变化提供了借鉴.

     

INVERSION OF MOISTURE PROFILES BY A NONLINEAR ITERATIVE PHYSICAL RETRIEVAL*

The Advanced TIROS-N Operational Vertical Sounder(ATOVS) measurements are used to generate the atmospheric parameters,such as temperature and moisture profiles,under both clear and cloudy situations.This paper describes briefly the nonlinear iterative physical retrieval method.By using this retrieval scheme,an experiment has been carried out to retrieve the moisture profiles from ATOVS measurements on the NOAA-16 satellite for July of 2002.ATOVS profile retrieval results are evaluated by root mean square(RMS) differences with respect to RAdiosonde OBservation(RAOB) profiles.The accuracy of the retrieval is about 15%-23% for the relative humidity profile in this study.     

用GPS监测杭州湾跨海大桥沉降的可行性分析

杭州湾跨海大桥建成通车后,原有的利用水准测量进行沉降监测的方式遇到了很大困难。针对这种情况,本文从理论上推导了使用GPS静态测量代替水准测量进行沉降监测带来的差别,并通过数值分析证明了对于杭州湾跨海大桥这种差别在1mm以内。最后对两者的实际测量精度情况进行了分析,得出两者在杭州湾跨海大桥沉降监测中测量精度相当。     

Spatio‐temporal variability of water and energy fluxes – a case study for a mesoscale catchment in pre‐alpine environment

Water and energy fluxes at and between the land surface, the subsurface and the atmosphere are inextricably linked over all spatio‐temporal scales. Our research focuses on the joint analysis of both water and energy fluxes in a pre‐alpine catchment (55 km²) in southern Germany, which is part of the Terrestrial Environmental Observatories (TERENO). We use a novel three‐dimensional, physically based and distributed modelling approach to reproduce both observed streamflow as an integral measure for water fluxes and heat flux and soil temperature measurements at an observation location over a period of 2 years. While heat fluxes are often used for comparison of the simulations of one‐dimensional land surface models, they are rarely used for additional validation of physically based and distributed hydrological modelling approaches. The spatio‐temporal variability of the water and energy balance components and their partitioning for dominant land use types of the study region are investigated. The model shows good performance for simulating daily streamflow (Nash–Sutcliffe efficiency > 0.75). Albeit only streamflow measurements are used for calibration, the simulations of hourly heat fluxes and soil temperatures at the observation site also show a good performance, particularly during summer. A limitation of the model is the simulation of temperature‐driven heat fluxes during winter, when the soil is covered by snow. An analysis of the simulated spatial fields reveals heat flux patterns that reflect the distribution of the land use and soil types of the catchment. The water and energy partitioning is characterized by a strong seasonal cycle and shows clear differences between the selected land use types. Copyright © 2016 The Authors Hydrological Processes Published by John Wiley & Sons Ltd.     

3D soil structure of the Mygdonian basin for site response analysis

The 3D structure of the Mygdonian sedimentary basin (N. Greece) is investigated. The aim of this study is to propose a 3D model of this sedimentary structure that can later be used to model the seismic records currently being obtained by the permanent accelerograph network operating in the area. This model builds on previous efforts and incorporates new data. The geometry and dynamic properties of the soil layers were inverted using data from microtremor array measurements, seismic refraction profiles, boreholes, and geotechnical investigations. Phase-velocity dispersion curves of Rayleigh waves were determined at 27 sites in the basin using the spatial autocorrelation method (SPAC) introduced by Aki [1]. S-wave velocity profiles were inverted from these dispersion curves and the whole valley structure was interpolated using our new results and all previously available data. The proposed 3D model describes the geometry and shear-wave velocities of the Mygdonian and pre-Mygdonian sedimentary systems, and the top bedrock surface. Our results indicate that this 3D model correctly reflects the geometry and dynamic properties of the sedimentary layers. The case of Euroseistest, where the subsoil structure is the result of bringing together many disparate data, could be used as an example for similar alluvial basins throughout the world, where usually only scarce data is available.     

Basaltic thermals and Subplinian plumes: Constraints from acoustic measurements at Shishaldin volcano, Alaska

The 1999 basaltic eruption of Shishaldin volcano (Alaska, USA) included both Strombolian and Subplinian activity, as well as a “pre-Subplinian” phase interpreted as the local coalescence within a long foam in the conduit. Although few visual observations were made of the eruption, a great deal of information regarding gas velocity, gas flux at the vent and plume height may be inferred by using acoustic recordings of the eruption. By relating acoustic power to gas velocity, a time series of gas velocity is calculated for the Subplinian and pre-Subplinian phases. These time series show trends in gas velocity that are interpreted as plumes or, for those signals lasting only a short time, thermals. The Subplinian phase is shown to be composed of a thermal followed by five plumes with a total expelled gas volume of .The initiation of the Subplinian activity is probably related to the arrival of a large overpressurised bubble close to the top of the magma column. A gradual increase in low-frequency (0.01–0.5 Hz) signal prior to this “trigger bubble” may be due to the rise of the bubble in the conduit. This delay corresponds to a reservoir located at ≈3.9 km below the surface, in good agreement with studies on other volcanoes.The presence of two thermal phases is also identified in the middle of the pre-Subplinian phase with a total gas release of and . Gas velocity at the vent is found to be and for the Subplinian plumes and the pre-Subplinian thermals respectively.The agreement is very good between estimates of the gas flux from modelling the plume height and those obtained from acoustic measurements, leading to a new method by which eruption physical parameters may be quantified. Furthermore, direct measurements of gas velocity can be used for better estimates of the flux released during the eruption.     

Petrological model of the northern Izu–Bonin–Mariana arc crust: constraints from high-pressure measurements of elastic wave velocities of the Tanzawa plutonic rocks, central Japan

Ultrasonic compressional wave velocities (Vp) and shear wave velocities (Vs) were measured with varying pressure up to 1.0 GPa in a temperature range from 25 to 400 °C for a suite of tonalitic–gabbroic rocks of the Miocene Tanzawa plutonic complex, central Japan, which has been interpreted as uplifted and exposed deep crust of the northern Izu–Bonin–Mariana (IBM) arc. The Vp values of the tonalitic–gabbroic rocks increase rapidly at low pressures from 0.1 to 0.4 GPa, and then become nearly constant at higher pressures above 0.4 GPa. The Vp values at 1.0 GPa and 25 °C are 6.3–6.6 km/s for tonalites (56.4–71.1 wt.% SiO₂), 6.8 km/s for a quartz gabbro (53.8 wt.% SiO₂), and 7.1–7.3 km/s for a hornblende gabbro (43.2–47.7 wt.% SiO₂). Combining the present data with the P wave velocity profile of the northern IBM arc, we infer that 6-km-thick tonalitic crust exists at mid-crustal depth (6.1–6.3 km/s Vp) overlying 2-km-thick hornblende gabbroic crust (6.8 km/s Vp). Our model shows large differences in acoustic impedance between the tonalite and hornblende gabbro layers, being consistent with the strong reflector observed at 12-km-depth in the IBM arc. The measured Vp of Tanzawa hornblende-bearing gabbroic rocks (7.1–7.3 km/s) is significantly lower than that Vp modeled for the lowermost crustal layer of the northern IBM arc (7.3–7.7 km/s at 15–22 km depth). We propose that the IBM arc consists of a thick tonalitic middle crust and a mafic lower crust.     

Minaret behavior under earthquake loading: The case of historical Istanbul

Minarets are very slender structures with an old existence. The historical ones are made of cut‐stone‐block masonry assembled in peripheral cylindrical wall with an interior helicoidal stair supported on a central core and on the wall. They are spread throughout the Islamic world and constitute an important heritage not only of religious value, but also of great cultural interest. Throughout the times, these structures as part of a mosque, have suffered significant damage during the earthquakes. Istanbul presents interesting characteristics to evaluate their dynamic behavior, as they are in great number, in an area where a large event in the next 30 years has been predicted. In this paper, we performed a series of in situ ambient vibration tests to old minarets of various sizes and compared results of frequencies with numerical modeling of the same structures. For the low‐amplitude motion, the frequency values of the first modes can be obtained from an empirical formulae function of the inertia of the cross‐section and of the height of the main ‘body.’ Damping ratios for these amplitudes are of the order of 0.5–1.0%. Dynamic linear analyses of these structures indicate that for most cases very high stresses develop for PGA above 0.5 g, an input with a reasonable chance of occurring in the next 30 years. These high stresses are expected to cause the toppling of the minarets in the form that has been observed in the recent past events. Copyright © 2011 John Wiley & Sons, Ltd.     

Information content of snow hydrological signatures based on streamflow,precipitation and air temperature

Hydrological signatures that represent snow processes are valuable to gain insights into snow accumulation and snow melt dynamics. We investigated five snow signatures. Considering inter-annual average of each calendar day, two slopes derived from the relation between streamflow and air temperature for different periods and streamflow peak maxima are used as signatures. In addition, two different approaches are used to compute inter-annual average and yearly snow storage estimates. We evaluated the ability of these signatures to characterize average (a) snow melt dynamics and (b) snow storage. They were applied in 10 Critical Zone Observatory catchments of the Southern Sierra mountains (USA) characterized by a Mediterranean climate. The relevance and information content of the signatures are evaluated using snow depth and snow water equivalent measurements as well as inter-catchment differences in elevation. The slopes quantifying the relations between streamflow and air temperature and the date of streamflow peak were found to characterize snow melt dynamics in terms of snow melt rates and snow melt affected areas. Streamflow peak dates were linked to the period of highest snow melt rates. Snow storage could be estimated both on average, considering all years, and for each year. Snow accumulation dynamics could not be characterized due to the lack of streamflow response during the snow accumulation period. The signatures were found potentially valuable to gain insights into catchment scale snow processes. In particular, when comparing catchments or observed and simulated data, they could provide insights into differences in terms of (a) snow melt rate and/or snow melt affected area over the snow melt season and (b) average or yearly snow storage. Requiring only widely available data, these hydrological signatures can be valuable for snow processes characterization, catchment comparison/classification or model development, calibration or evaluation.     

高分五号可见短波红外高光谱相机在轨辐射性能评估

对遥感器及其图像的在轨辐射性能(信噪比、相对辐射定标精度、绝对辐射定标精度和动态范围)评估是检验遥感器定量应用能力的重要任务之一。本文结合高分五号卫星可见短波红外高光谱相机AHSI (the Advanced Hyperspectral Imager)在轨性能评估任务,依据卫星发射以来的在轨测试数据,介绍了AHSI相机在轨辐射性能评估的原理、方法及相应测试情况。测试结果表明:AHSI信噪比可见近红外最高达到近700,短波红外最高达到近500;相对辐射定标精度误差小于0.5%,星上绝对辐射定标不确定度小于3%,场地绝对辐射定标真实性检验精度误差小于5%;动态范围在轨可见短波均可以256档增益精细调整。AHSI在轨辐射性能良好且稳定,能够有效支持后续定量化应用需求。