Geoid determination using adapted reference field, seismic Moho depths and variable density contrast

 The traditional remove-restore technique for geoid computation suffers from two main drawbacks. The first is the assumption of an isostatic hypothesis to compute the compensation masses. The second is the double consideration of the effect of the topographic–isostatic masses within the data window through removing the reference field and the terrain reduction process. To overcome the first disadvantage, the seismic Moho depths, representing, more or less, the actual compensating masses, have been used with variable density anomalies computed by employing the topographic–isostatic mass balance principle. In order to avoid the double consideration of the effect of the topographic–isostatic masses within the data window, the effect of these masses for the used fixed data window, in terms of potential coefficients, has been subtracted from the reference field, yielding an adapted reference field. This adapted reference field has been used for the remove–restore technique. The necessary harmonic analysis of the topographic–isostatic potential using seismic Moho depths with variable density anomalies is given. A wide comparison among geoids computed by the adapted reference field with both the Airy–Heiskanen isostatic model and seismic Moho depths with variable density anomaly and a geoid computed by the traditional remove–restore technique is made. The results show that using seismic Moho depths with variable density anomaly along with the adapted reference field gives the best relative geoid accuracy compared to the GPS/levelling geoid. Received: 3 October 2001 / Accepted: 20 September 2002 Correspondence to: H.A. Abd-Elmotaal     

Atmospheric Methyl Iodide at Cape Grim, Tasmania, from AGAGE Observations

Atmospheric mixing ratios of methyl iodide (CH₃I) and other methyl halides have been measured at Cape Grim, Tasmania (41°S, 145°E), since early 1998 as part of the Advanced Global Atmospheric Gases Experiment (AGAGE). This paper analyses about 1700 ambient air CH₃I measurements from the 14-month period (March 1998–April 1999). Mixing ratios peaked during the summer, despite faster photolytic loss, suggesting local oceanic emissions were about 2.2–3.6 times stronger in summer than in winter. Back trajectories show that CH₃I levels are strongly dependent on air mass origin, with highest mixing ratios in air from the Tasman Sea/Bass Strait region and lowest levels in air originating from the Southern Ocean at higher latitudes. CH₃I mixing ratios were not well correlated with other methyl halides in unpolluted marine air. The large variations with season and air mass origin suggest that high frequency, continuous data from key locations will make a significant contribution to the understanding of sources and sinks of this important short-lived atmospheric species.     

测氡法快速确定油气田边界及深度

本介绍了运用测氡法快速确定大庆××油气田边界，估算其埋藏深度试验，结果表明，该方法具有可行性和实用性。由于所做工作有限，尚属经验性探讨，还必须从理论和实践上进一步地工作，进而充实、完善它。     

X射线荧光分析技术在喀拉通克铜镍矿井下现场品位测定

文章主要介绍应用 X射线荧光现场取样技术在新疆喀拉通克铜镍矿井下现场测定铜镍品位 ,快速评价矿石质量和降低工人劳动强度的方法和效率     

热液矿床石英铅同位素组成及其地质意义

作者以若尔盖铀矿床为例，研究了含矿热液形成的石英脉石英的铅同位素组成，并将其作为联系母源铅同位素组成的桥梁，判别铀的来源。结果表明，矿床中石英铅同位素组成与含矿黄铁矿和中酸性构造－岩浆成因的花岗岩铅同位素组成具线性演化关系。由此提出含矿热液中的铀来自中酸性构造－岩浆岩而不是地层岩石的新见解，同时提出利用热液石英铅同位素组成判别非放射性矿床成矿元素来源的可能性。     

微波焙烧炉在分析测试中的应用研究

本文详细论述了微波焙烧炉代替马弗炉应用于样品焙烧、熔融、活性炭灰化工作中的实际效果。结果表明：其应用不但可行，而且与马弗炉相比，微波焙烧炉具有更加优越的经济性与环保效果。     

药用滑石粉酸中可溶物测定方法考察

考察药用滑石粉酸中可溶物测定方法的重复性、耐用性 ,分析主要影响因素。比较酸溶物提取液滤过介质对测定结果差异的影响 ;采用重量法随机测定酸溶物含量和室间差异。两种滤过介质处理对测定结果没有显著差异 ;室间测定结果没有显著差异 ;30批样品平行测定结果的 RSD值范围为 0 %～ 18.2 %。酸中可溶物测定法存在重复性和耐用性不佳的问题 ,应相应调整酸中可溶物含量限度     

河北省物理地层界线厘定

以现代地层学多重划分为理论依据,以岩石地层单元组的密度、磁化率、剩余磁化强度及厚度加权算术平均值等物性参数为研究对象,以有序地质量最优分割方法为数学手段,进行河北省全区综合地层柱物理地层界线的厘定,并对其地质意义进行了初步讨论。     

北斗卫星导航系统双差动力法精密定轨及其精度分析

针对GEO卫星切向轨道分量与双差模糊度强相关的问题,对经典双差动力法进行了改进,提出联合使用载波相位和相位平滑伪距实现北斗系统精密定轨,并从理论上分析了以上处理策略的可行性及对模糊度固定的影响,然后结合北斗系统精密定轨特点,推导给出了利用QIF方法实现北斗卫星双差模糊度固定的基本原理,实测数据分析表明:联合载波相位和相位平滑伪距,既可降低相关性,又可兼顾精度,定轨效果优于经典双差动力法;利用QIF方法能够取得一定的模糊度固定效果,但受观测条件限制,北斗卫星双差模糊度固定成功率整体不高,双差模糊度固定之后对轨道的改进作用有限。