MODEL-BASED TRANSFORMATIONS OF COMMON MIDPOINT GATHERS1

A method for transforming Normal Moveout corrected CMP-gathers is proposed. The method is based upon the availability of a model of the CMP-gather. However, the transformation can be performed with any degree of accuracy in the model. Ideally the employed model should be a synthesis of all available a priori information about the particular data set. Mathematically the transformation is performed as follows. The CMP-gather is considered to be a matrix. This matrix is first decomposed into a set of submatrices of the same dimensions. Each submatrix consists of non-zero elements or samples with the same relative amount of noise. By reducing each of these submatrices to a vector (a trace) we get a new set of traces. This set then represents the transformed CMP-gather. The purpose of the transformation is to organize the CMP data in a form which makes it easier both to analyse the noise distribution and to take the necessary steps to improve the signal-to-noise ratio at the stacking stage. In principle the method incorporates the exploitation of multichannel recordings with the use of models. Several examples of transformed gathers and their applications to the improvement of real seismic data are shown.     

白云鄂博碳酸岩墙的稀土和微量元素地球化学及对其成因的启示

根据矿物组成白云鄂博矿区的碳酸岩岩可墙可分为白云石型、白云石－方解石共存型和方解石型三种类型。REE和微量元素地球化学表明，这三类碳酸岩岩墙为碳酸岩浆演化不同阶段的产物，白云石型和白云石－方解石共存型对应于早期岩浆阶段，其（La/Nd)n、(La/Yb)n比值随稀土总量的增加而增大，方解石型则对应于碳酸岩浆演化的晚期热液阶段，其稀土总量明显富集，但其（La/Nd)n、(La/Y)n和（La/Yb)n比值随稀土总量的增加却有减小的趋势，热液阶段也是白云鄂博稀土矿化的主要阶段。     

Modelling for forest growing stock assessment using satellite data — A case study

The satellite digital vegetation index data has been correlated with the forest growing stock by fitting linear regression models. The goodness of fit was tested. The analysis showed that the vegetation index which is the ratio of reflectance of vegetation in near infrared band to red wave band of electromagnetic spectrum is highly correlated to forest growing stock and the same can be used to predict the volume in remote forest areas for quick assessment purpose. Implications for future forest inventory are discussed.     

SUPERSTACK—AN ITERATIVE STACKING ALGORITHM*

An algorithm for separation of signals according to their coherency is proposed. The algorithm, called Superstack, is used on common depth point data after normal moveout corrections have been applied. The algorithm can be regarded as an iterative stacking procedure. After each stack, input values are changed depending on the consistency of the output of the previous stack. The Superstack algorithm is able to provide better separation of signals showing a different degree of horizontal consistency (coherency) than the normal horizontal stack. All noise signals in a CDP-gather may be assumed to show less horizontal consistency than the primary reflections. On this basis the algorithm will give an improved primary/multiple and an improved primary/noise ratio. The Superstack is very general, should not be especially expensive in terms of computer time, and can easily be implemented in routine processing.     

白云鄂博碳酸岩的方解石-白云石地质温度计

利用方解石-白云石地质温度计对白云鄂博地区碳酸岩的平衡温度进行了测定。出露于东矿下盘的白云岩质火山岩和出露于尖山的方解石-白云石型火山岩获得了较高的温度,分别为681℃和648℃。这些样品中的方解石呈二十微米左右晶形较完整的小片,被稍大粒度的白云石颗粒包裹,未受交代作用影响,推测这种碳酸岩在快速冷却的情况下保存下了其岩浆侵位时的成分特点,从而指示出接近碳酸岩浆侵位时的温度。但本区多数碳酸岩的平衡温度在400～500℃之间,有下列三种情况:(1)具有自形-半自形中粗粒粒状变晶结构的碳酸岩最后的平衡温度为415～496℃;(2)产自东矿的其余样品(火山岩),所测最后平衡温度为431～485℃,在测温的微区范围内可见极细粒白云石方解石与稀土等矿物共生的现象;(3)为交代重结晶结构的碳酸岩明显受到后期热液流体的交代,在流体的作用下共生方解石和白云石在成分上达到新的平衡,平衡温度为432～507℃。本文所分析的样品多数结果(371～507℃)与用白云石(方解石)和磁铁矿氧同位素温度计对白云鄂博碳酸岩的计算结果(360～546℃)十分一致。虽然有研究者对方解石-白云石温度计用于火成碳酸岩表示过质疑,但本文资料表明火成碳酸岩最后的平衡温度是可以运用方解石-白云石温度计法来计算的。     

Application of directional filtering in lineament mapping for groundwater prospecting around bhinmal — A semi arid part of thar desert

The significance of neotectonic lineaments for groundwater prospecting was studied for the area around Bhinmal — a semi-arid part of Thar desert. The application of Directional Filtering procedures on IRS LISS I Band 4 digital image of the study area revealed NE-SW, NW-SE and E-W trending lineaments which are very subtle and in two cases, even unnoticed otherwise. The use of exploratory borehole lithologs and field evidences indicated that the identified lineaments are long rectilinear buried and partly exposed channels and the intersection zones are characterised by thick lenses of coarse sand and gravel. These buried channels and zones of coarse sediments thus represent potential sites for the accumulation of freshwater during rain. The present work has highlighted the suitability of Directional Filtering procedures for lineament mapping and buried channel studies in a desertic terrain.     

内蒙古白云鄂博地区基底岩石锆石年代学及对构造背景的指示

白云鄂博地区的克拉通基底岩石主要由糜棱岩化花岗片麻岩(2588±15Ma),正长岩、花岗闪长岩(2018±15Ma)和黑云母花岗片麻岩、含石榴石蓝晶石花岗片麻岩(～1890Ma)等组成,白云鄂博超大型稀土矿床就位于华北克拉通太古代基底之上。太古代克拉通基底在早元古代中晚期(2.0Ga)又经历了一次强烈的碰撞造山运动,造成了闪长质与花岗质岩浆侵位,以及1.9Ga片麻岩相变质事件。     

Cloud condensation nuclei spectra derived from size distributions and hygroscopic properties of the aerosol in coastal south-west Portugal during ACE-2

In this work we propose and test a method to calculate cloud condensation nuclei (CCN) spectra based on aerosol number size distributions and hygroscopic growth factors. Sensitivity studies show that this method can be used in a wide variety of conditions except when the aerosol consist mainly of organic compounds. One crucial step in the calculations, estimating soluble ions in an aerosol particle based on hygroscopic growth factors, is tested in an internal hygroscopic consistency study. The results show that during the second Aerosol Characterization Experiment (ACE-2) the number concentration of inorganic ions analyzed in impactor samples could be reproduced from measured growth factors within the measurement uncertainties at the measurement site in Sagres, Portugal.
CCN spectra were calculated based on data from the ACE-2 field experiment at the Sagres site. The calculations overestimate measured CCN spectra on average by approximately 30%, which is comparable to the uncertainties in measurements and calculations at supersaturations below 0.5%. The calculated CCN spectra were averaged over time periods when Sagres received clean air masses and air masses influenced by aged and recent pollution. Pollution outbreaks enhance the CCN concentrations at supersaturations near 0.2% by a factor of 3 (aged pollution) to 5 (recent pollution) compared to the clean marine background concentrations. In polluted air masses, the shape of the CCN spectra changes. The clean spectra can be approximated by a power function, whereas the polluted spectra are better approximated by an error function.     

Land transformation in Punjab — A case study of Kapurthala district

The map showing the extent of salt affected and sand dune soils was prepared at 1:50,000 scale using Landsat TM data for March 1987 and compared with the soil map of Kapurthala district based on 1965 aerial photographs and semi detailed survey of the district during 1975–76. The study revealed that in a span of 22 years (1965 to 1986) the area of sand dunes decreased from 22.7 per cent to 2.3 per cent and that of salt affected soils from 20.95 per cent to 4.38 per cent respectively as a consequence of reclamation of salt affected soils and clearing and levelling of sand dunes. Salt affected soils after reclamation have been brought under paddy-wheat rotation. Whereas sand dunes after clearing and levelling, have been brought under wheat or wheat -rice/fodder/oilseed crops.