Martian gravity field model and its time variations from MGS and Odyssey data

We present results of several years of research and data processing aimed at modelling the Mars gravity field and its longest wavelength time variations. The new solution includes tracking data from Mars Global Surveyor (MGS) from 1998 to 2006 (end of mission) and from Mars Odyssey from 2002 to the spring of 2008; this is the longest analyzed data set from these two orbiter missions as compared to previous works. The new model has been obtained by a team working in Europe, independently from the works of groups at NASA Jet Propulsion Laboratory (JPL) and Goddard Space Flight Center (GSFC), also with totally independent software. Observations consist in two and three-way Doppler measurements (also one way for MGS), and range tracking data collected by the Deep Space Network and have been processed in 4 day arcs, taking into account all disturbing forces of gravitational and non-gravitational origins; for each arc the state vector, drag and solar pressure model multiplying factors, and angular momentum dump parameters are adjusted. The static field (MGGM08A) is represented in spherical harmonics up to degree and order 95 and is very close to previously published models (in terms of spectral components and also over specific features); correlations with the global Mars topography are established and apparent depths of compensation by degree are derived. Lumped zonal harmonics of degree two and three are solved for every 10 days, exhibiting variations in line with previous results (including authors’ ones); the work also shows the difficulty of finding clean signatures (annual and semi-annual) for the zonal coefficient of second degree. The k₂ Love number is also derived from the ensemble of data, as well as from subsets of them; values between 0.110 and 0.130 are found, which are consistent with the existence of a Martian fluid core of significant radius.     

Long term variations in solar flare activity

A statistical analysis of the contemporary (1954-1975) solar flare particle events has been made for the parametersF (integrated, proton fluence in cm^-2 in an event with kinetic energy above 10 MeV) andR ₀ (the characteristic rigidity). These data are compared with the long-term averaged values determined from stable- and radio-nuclide measurements of lunar samples. The analysis shows that the ancient solar flare proton spectrum was harder (higher R₀ values) compared to that observed in contemporary flares. A similar analysis can not be made for the mean long-term averaged flux (ˉJ, cm^-2 S^-1), since the contemporary averages suffer from an uncertainty due to the statistics of a single event. However, the average flux estimates for time durations 〈T〉 exceeding 10³ yr, are free from such uncertainties. The long-term averaged ˉJ values obtained over different time scales (10⁴ - 10⁶ yr) suggest a possible periodic variation in solar flare activity, with enhanced flux level during the last 10⁵ yr. The available data rule out the occurrence of giant flares, with proton fluence exceeding 10¹⁵ cm^-2 during the last million years.     

泸沽湖沉积物中磷累积的时空变化及其环境意义

湖泊沉积物中磷累积特征反映了流域人类活动影响下的磷入湖通量的变化,与湖泊生态环境密切相关。本研究分析了泸沽湖15根长17~27cm沉积短岩芯中磷的含量,评估了自然源与人为源磷的贡献,探讨了近140年来不同来源磷累积的时空变化特征及其与流域人类活动和湖泊生态环境的关系。结果表明,不同湖区沉积物中磷含量垂向变化趋势总体一致。以南部湖心区LGS岩芯为例,1960年前,沉积物中磷的含量与累积通量较低,为人类活动干扰较弱的准自然沉积;1960~2000年,自然源与人为源磷的含量和累积通量均逐渐增加,其中1960~1980年和1980~2000年人为源磷累积通量平均分别为4.9mg/(m²·a)和39.1mg/(m²·a)。2000年以来,沉积物中自然源磷的累积通量略有降低,但人为源磷的累积通量持续升高,平均为109mg/(m²·a)。空间上,南部湖区自然和人为源磷的累积通量总体上高于北部湖区,不同时期自然源磷的累积通量高值区均位于南部湖区东部,而沿岸居民点密集分布的南北湖区连接处和西北部湖区人为源磷的累积通量相对较高。不同来源磷累积通量的时空变化主要与农业和旅游业发展导致的土壤侵蚀和污染排放输入有关。沉积物中磷累积通量与硅藻、摇蚊等水生生物属种呈同步的历史变化趋势,指示了磷输入对湖泊生态环境变化的重要影响。

     

When are relative variograms useful in geostatistics?

The relative variogram has been employed as a tool for correcting a simple kind of nonstationarity, namely that in which local variance is proportional to local mean squared. In the past, this has been linked in a vague way to the lognormal distribution, although if {Z_t; t D}is strongly stationary and normal over a domain D,then clearly {exp (Z_t); t D}will stillbe stationary, but lognormal. The appropriate link is made in this article through a universal transformation principle. More general situations are considered, leading to the use of a scaled variogram.     

Seasonal variations and mechanism for environmental control of NEE of CO_2 concerning the Potentilla fruticosa in alpine shrub meadow of Qinghai-Tibet Plateau

The study by the eddy covariance technique in the alpine shrub meadow of the Qing-hai-Tibet Plateau in 2003 and 2004 showed that the net ecosystem carbon dioxide exchange (NEE) exhibited noticeable diurnal and annual variations, with more distinct daily changes during the warmer seasons. The CO2 emission of the shrub ecosystem culminated in April and September while the CO2 absorption capacity reached a maximum in July and August. The absorbed carbon dioxide during the two consecutive years was 231.4 and 274.8 g CO2·m-2 respectively, yielding an average of 253.1 gCO2·m-2 per year: that accounts for a large proportion of absorbed CO2 in the region. Obviously, the diurnal carbon flux was negatively related to temperature, radiation and other atmospheric factors. Still, minute discrepancies in kurtosis and duration of carbon emission/absorption were detected between 2003 and 2004. It was found that the CO2 flux in the daytime was similarly affected by photosynthetic photon flux density in both years. Temperature appears to be the most important determinant of CO2 flux: specifically, the high temperature during the plant growing season inhibits the carbon absorption capacity. One potential explanation is that soil respiration is enhanced under such condition. Analysis of biomass revealed that the annual net carbon fixed capacity of aboveground and belowground biomass was 544.0 in 2003 and 559.4 g Cm"2 in 2004, which coincided with the NEE absorption capacity (63.1 g C·m-2 in 2003 and 74.9 g C·m-2 in 2004) in the corresponding plant growing season.     

Multi-threaded compression of Earth observation time-series data

ABSTRACT

Earth observation data are typically compressed using general-purpose single-threaded compression algorithms that operate at a fraction of the bandwidth of modern storage and processing systems. We present evidence that recently developed multi-threaded compression codecs offer substantial benefits over widely used single-threaded codecs in terms of compression efficiency when applied to a selection of moderate resolution imaging spectroradiometer (MODIS) datasets stored in the HDF5 format. Compression codecs from the LZ77 and Rice families are shown to vary in efficacy when applied to different MODIS data products, highlighting the need for compression strategies to be tailored to different classes of data. We also introduce LPC-Rice, a new multi-threaded codec, that performs particularly well when applied to time-series data.     

求定CG-5型重力仪静态漂移常数的方法研究

介绍了如何利用仪器的试验数据文件,在MATLAB中绘制静态漂移曲线和残余零漂曲线图的方法.设计了一款GUI用户界面,并给出了两种精确计算漂移常数数值的方法.通过多台仪器计算对比,该方法能够较好地检验仪器静态漂移特性.     

Évolution de l'onde semi-diurne M2 de la marée à Brest de 1846 à 2005

The work of searching, recovering and quality control of ancient sea-level measurements at Brest is presented. This work enables us to complete a study carried out by Cartwright in 1972, which showed a decrease in the tidal M2 semi-diurnal amplitude of 1% per century. After including these ancient data, as well as the last four decades of observations in the analysis, our results show an increase of the amplitude of M2 after 1960 and a decrease before 1880, suggesting a long-period oscillation rather than a steady secular trend. To cite this article: N. Pouvreau et al., C. R. Geoscience 338 (2006).     

Enhanced Oxygen Isotope Determination in Uranium Oxides Using BrF5 Fluorination

A new method for accurate determination of oxygen isotopes in uranium oxides encountered in the nuclear fuel cycle was developed using the conventional BrF₅ fluorination technique. Laser‐assisted fluorination was tested for comparison. We focused on fine powders of triuranium octoxide (U₃O₈), uranium dioxide (UO_2±x with 0 ≤ x ≤ 0.25), uranium trioxide (UO₃.nH₂O, with 0.8 ≤ n ≤ 2) and diuranates (M₂U₂O₇.nH₂O, with M = NH₄, Na or Mg_0.5 and 0 ≤ n ≤ 6). Fluorination at room temperature and heating under vacuum at 150 °C are shown to eliminate both adsorbed and structural water from the powder samples. Precision fit for purpose of δ¹⁸O values (± 0.3‰, 1s) and oxygen yields (close to 100%) were obtained for U₃O₈ and UO₂ where oxygen is only bound to uranium. A lower precision was observed for UO₃.nH₂O and M₂U₂O₇.nH₂O where oxygen is both present in the structural H₂O and bonded to uranium and where the extracted O_2(g) can be contaminated by NF₃ and NO_x compounds. Laser‐assisted fluorination gave shifted δ¹⁸O values between +0.8 and +1.4‰ for U₃O₈, around ?0.8‰ for UO₃.nH₂O and between ?3.9 and ?4.5‰ for M₂U₂O₇.nH₂O (± 0.3‰, 1s) compared with the conventional method.     

基于GRACE卫星测量得到的中国及其周边地区陆地水量变化

GRACE卫星成功开辟了空间大地测量对地观测的新途径。利用GRACE卫星得到的时变地球重力资料,分析估计了中国及其周边地区陆地水量的变化趋势,较为清晰地揭示了该地区季节性变化特征。进一步采用13点滑动平均的方法扣除了季节性变化,提取了4个特征区域(喜马拉雅南部,新疆与西藏及其周边的亚洲高山区域,中国华北、东北地区和中国南部地区)的陆地水量变化特征信息,这4个区域陆地水量的变化趋势分别为-12.7±0.7、-60.4±2.7、-12.5±0.5和6.6±0.9 km³/a。其中：喜马拉雅南部和亚洲高山区域陆地水量呈现明显的衰减趋势,与Matsuo和Heki模拟冰川质量损失源得到的结果较为一致;但近10年来亚洲高山区域西北部冰川加速融化趋势并不明显。中国华北、东北地区和南部地区水量变化比较复杂,具不稳定的变化趋势。