Regularized derivatives of potential fields and their role in semi-automated interpretation methods

Evaluation of higher derivatives (gradients) of potential fields plays an important role in geophysical interpretation (qualitative and/or quantitative), as has been demonstrated in many approaches and methods. On the other hand, numerical evaluation of higher derivatives is an unstable process – it has the tendency to enlarge the noise content in the original data (to degrade the signal-to-noise ratio). One way to stabilize higher derivative evaluation is the utilization of the Tikhonov regularization. In the submitted contribution we present the derivation of the regularized derivative filter in the Fourier domain as a minimization task by means of using the classical calculus of variations. A very important part of the presented approach is the selection of the optimum regularization parameter – we are using the analysis of the C-norm function (constructed from the difference between two adjacent solutions, obtained for different values of regularization parameter). We show the influence of regularized derivatives on the properties of the classical 3D Euler deconvolution algorithm and apply it to high-sensitivity magnetometry data obtained from an unexploded ordnance detection survey. The solution obtained with regularized derivatives gives better focused depth-estimates, which are closer to the real position of sources (verified by excavation of unexploded projectiles).     

The Velocity Field and Kinematics of the Galaxy NGC 784 in the Hα Line

In this paper we present the H map, the 2D velocity field and the rotation curve of the galaxy NGC 784 obtained with the ByuFOSC2 scanning Fabry-Perot interferometer, attached at the prime focus of the 2.6-m telescope of Byurakan Observatory. The H image shows several HII condensations along the major axis of the galaxy. The galaxy has an asymmetric distribution of the H emission. The rotation curve is quite symmetric with a low gradient in the central part of the galaxy.     

Evidence for short term changes in the intensity and spectrum of hard X-rays from Cyg X-1

The paper presents experimental evidence for the existence of fast intensity fluctuations with time scales of the order of a minute in the X-ray emission from Cyg X-1 at energies greater than 29 keV. Spectral variations over time intervals of 20–25 min are also observed in the same energy range. Whereas, similar intensity and spectral fluctuations have been reported earlier at lower energies the observations presented here is the first evidence for the existence of similar fluctuations at high energies.     

Neutron activation analysis of the 1965 taal volcanic ash

Neutron activation analysis of the Taal volcanic ash revealed the presence of unusual amount of scandium in the volcanic ash as compared to the standard basalt BCR-1. The BCR-1 value for Fe/Sc is 2760 while that of Taal ash is about 2649. It is suggested that the eruption was probably characterized by the ejection of scandium-rich materials. Scandium may be used as supplementary evidence in evaluating an impending future Taal volcanic activity.     

Dunes on Titan observed by Cassini Radar

Thousands of longitudinal dunes have recently been discovered by the Titan Radar Mapper on the surface of Titan. These are found mainly within ±30° of the equator in optically-, near-infrared-, and radar-dark regions, indicating a strong proportion of organics, and cover well over 5% of Titan's surface. Their longitudinal duneform, interactions with topography, and correlation with other aeolian forms indicate a single, dominant wind direction aligned with the dune axis plus lesser, off-axis or seasonally alternating winds. Global compilations of dune orientations reveal the mean wind direction is dominantly eastwards, with regional and local variations where winds are diverted around topographically high features, such as mountain blocks or broad landforms. Global winds may carry sediments from high latitude regions to equatorial regions, where relatively drier conditions prevail, and the particles are reworked into dunes, perhaps on timescales of thousands to tens of thousands of years. On Titan, adequate sediment supply, sufficient wind, and the absence of sediment carriage and trapping by fluids are the dominant factors in the presence of dunes.     

Heavy rare gases from Rabbit Lake (Canada) and the Oklo mine (Gabon): natural spontaneous chain reactions in old uranium deposits

Xenon isotopic studies confirm natural spontaneous chain reactions at the Oklo mine site (Republic of Gabon) with an integrated neutron flux of approximately 4 × 10²⁰n/cm² and a duration between 14,000 and 70,000 years. Similar studies for the Rabbit Lake deposit (Saskatchewan), a slightly younger site with some evidence of continued geologic activity, shows no evidence of self-supporting reactions.     

Geochemical Prospectivity Mapping Through a Feature Extraction–Selection Classification Scheme

Natural Resources Research - Machine learning (ML) schemes can enhance success in geochemical prospectivity mapping. This study has examined the effectiveness of several feature extraction or...     

Paleohydrology and paleoclimate records in a saline prairie lake core: mineral,isotope and organic indicators

This pilot study examines the potential of obtaining a sedimentary record of paleoenvironmental/climatic/hydrologic conditions for saline Redberry Lake in southern Saskatchewan, Canada. The tools are mineralogy, stable isotopes and pigments. The upper meter of an offshore sediment core contains 10 to 20% by weight aragonite (CaCO₃), which apparently precipitated in the water column. The ¹⁸O and ¹³C of the bulk aragonite (corrected for content of detrital calcite) vary by 4 to 5. Enrichment in ¹⁸O in aragonite is significantly correlated with pigment concentrations (chlorophyll a, phaeophytin). The ¹⁸O and pigment data provide evidence for relatively dry and/or warm conditions and high limnetic productivity for the period 2500 to 1500 yrs B.P. After 1500 B.P., the climate was apparently similar to the present, with two episodes of relatively enhanced productivity, dryness and/or warmth, at around 1000 to 900 and 500 to 200 B.P. During the past century, Redberry Lake has decreased approximately 8 m in depth and its salinity has doubled. No clear sedimentary signal was observed in response to these recent hydrologic trends. These changes have not been associated with a significant climate trend in the region, but may have been induced by land use changes in the catchment.This publication is the third of a series of papers presented at the Conference on Sedimentary and Paleolimnological Records of Saline Lakes. This Conference was held August 13–16, 1991 at the University of Saskatchewan, Saskatoon, Canada. Dr. Evans is serving as Guest Editor for this series.     

Data base management system for erosivity values

In order to check the premature siltation of the reservoirs and guard against the drop in the irrigation potential, the Government of India has launched the schemes of soil conservation and integrated watershed management in the catchments of RVPs and Flood Prone rivers. Owing to the large financial and manpower commitments needed to implement and execute soil conservation measures over vast catchment areas, a priority approach for treatment was identified. The methodology developed for prioritization of watersheds of a catchment area conceptualizes sedimentation of the reservoirs as a multiplicative function of erosivity value and the delivery ratio. This paper deals with the development of a computerized data base software module ‘WEIGHT’ for determination of erosivity values for the mapping units comprising assemblages of the varying combinations of climate, physiography and slope, land use and cover conditions, soil characteristics (texture, solumn thickness, permeability and pH) and the existing erosion and soil conservation measures. The WEIGHT software package is coded in FORTRON-4 for PDP 11/83 operating system. the data base comprises storage of the attributes of the different erosivity determinants of the mapping units with predetermined erosivity values sequentially on a disk and comparing the attributes of a new mapping unit to get the most probabilities erosivity value. The objective has been to eliminate the personal bias and bring about the objectivity in the process of assigning erosivity values to the different mapping units. The data base design, design logic and operational sequence of the data base are discussed in the paper.